1 /*- 2 * CAM IO Scheduler Interface 3 * 4 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 5 * 6 * Copyright (c) 2015 Netflix, Inc. 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions, and the following disclaimer, 13 * without modification, immediately at the beginning of the file. 14 * 2. The name of the author may not be used to endorse or promote products 15 * derived from this software without specific prior written permission. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR 21 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27 * SUCH DAMAGE. 28 * 29 * $FreeBSD$ 30 */ 31 32 #include "opt_cam.h" 33 #include "opt_ddb.h" 34 35 #include <sys/cdefs.h> 36 __FBSDID("$FreeBSD$"); 37 38 #include <sys/param.h> 39 40 #include <sys/systm.h> 41 #include <sys/kernel.h> 42 #include <sys/bio.h> 43 #include <sys/lock.h> 44 #include <sys/malloc.h> 45 #include <sys/mutex.h> 46 #include <sys/sbuf.h> 47 #include <sys/sysctl.h> 48 49 #include <cam/cam.h> 50 #include <cam/cam_ccb.h> 51 #include <cam/cam_periph.h> 52 #include <cam/cam_xpt_periph.h> 53 #include <cam/cam_xpt_internal.h> 54 #include <cam/cam_iosched.h> 55 56 #include <ddb/ddb.h> 57 58 static MALLOC_DEFINE(M_CAMSCHED, "CAM I/O Scheduler", 59 "CAM I/O Scheduler buffers"); 60 61 static SYSCTL_NODE(_kern_cam, OID_AUTO, iosched, CTLFLAG_RD | CTLFLAG_MPSAFE, 0, 62 "CAM I/O Scheduler parameters"); 63 64 /* 65 * Default I/O scheduler for FreeBSD. This implementation is just a thin-vineer 66 * over the bioq_* interface, with notions of separate calls for normal I/O and 67 * for trims. 68 * 69 * When CAM_IOSCHED_DYNAMIC is defined, the scheduler is enhanced to dynamically 70 * steer the rate of one type of traffic to help other types of traffic (eg 71 * limit writes when read latency deteriorates on SSDs). 72 */ 73 74 #ifdef CAM_IOSCHED_DYNAMIC 75 76 static bool do_dynamic_iosched = true; 77 SYSCTL_BOOL(_kern_cam_iosched, OID_AUTO, dynamic, CTLFLAG_RD | CTLFLAG_TUN, 78 &do_dynamic_iosched, 1, 79 "Enable Dynamic I/O scheduler optimizations."); 80 81 /* 82 * For an EMA, with an alpha of alpha, we know 83 * alpha = 2 / (N + 1) 84 * or 85 * N = 1 + (2 / alpha) 86 * where N is the number of samples that 86% of the current 87 * EMA is derived from. 88 * 89 * So we invent[*] alpha_bits: 90 * alpha_bits = -log_2(alpha) 91 * alpha = 2^-alpha_bits 92 * So 93 * N = 1 + 2^(alpha_bits + 1) 94 * 95 * The default 9 gives a 1025 lookback for 86% of the data. 96 * For a brief intro: https://en.wikipedia.org/wiki/Moving_average 97 * 98 * [*] Steal from the load average code and many other places. 99 * Note: See computation of EMA and EMVAR for acceptable ranges of alpha. 100 */ 101 static int alpha_bits = 9; 102 SYSCTL_INT(_kern_cam_iosched, OID_AUTO, alpha_bits, CTLFLAG_RW | CTLFLAG_TUN, 103 &alpha_bits, 1, 104 "Bits in EMA's alpha."); 105 106 /* 107 * Different parameters for the buckets of latency we keep track of. These are all 108 * published read-only since at present they are compile time constants. 109 * 110 * Bucket base is the upper bounds of the first latency bucket. It's currently 20us. 111 * With 20 buckets (see below), that leads to a geometric progression with a max size 112 * of 5.2s which is safeily larger than 1s to help diagnose extreme outliers better. 113 */ 114 #ifndef BUCKET_BASE 115 #define BUCKET_BASE ((SBT_1S / 50000) + 1) /* 20us */ 116 #endif 117 static sbintime_t bucket_base = BUCKET_BASE; 118 SYSCTL_SBINTIME_USEC(_kern_cam_iosched, OID_AUTO, bucket_base_us, CTLFLAG_RD, 119 &bucket_base, 120 "Size of the smallest latency bucket"); 121 122 /* 123 * Bucket ratio is the geometric progression for the bucket. For a bucket b_n 124 * the size of bucket b_n+1 is b_n * bucket_ratio / 100. 125 */ 126 static int bucket_ratio = 200; /* Rather hard coded at the moment */ 127 SYSCTL_INT(_kern_cam_iosched, OID_AUTO, bucket_ratio, CTLFLAG_RD, 128 &bucket_ratio, 200, 129 "Latency Bucket Ratio for geometric progression."); 130 131 /* 132 * Number of total buckets. Starting at BUCKET_BASE, each one is a power of 2. 133 */ 134 #ifndef LAT_BUCKETS 135 #define LAT_BUCKETS 20 /* < 20us < 40us ... < 2^(n-1)*20us >= 2^(n-1)*20us */ 136 #endif 137 static int lat_buckets = LAT_BUCKETS; 138 SYSCTL_INT(_kern_cam_iosched, OID_AUTO, buckets, CTLFLAG_RD, 139 &lat_buckets, LAT_BUCKETS, 140 "Total number of latency buckets published"); 141 142 struct iop_stats; 143 struct cam_iosched_softc; 144 145 int iosched_debug = 0; 146 147 typedef enum { 148 none = 0, /* No limits */ 149 queue_depth, /* Limit how many ops we queue to SIM */ 150 iops, /* Limit # of IOPS to the drive */ 151 bandwidth, /* Limit bandwidth to the drive */ 152 limiter_max 153 } io_limiter; 154 155 static const char *cam_iosched_limiter_names[] = 156 { "none", "queue_depth", "iops", "bandwidth" }; 157 158 /* 159 * Called to initialize the bits of the iop_stats structure relevant to the 160 * limiter. Called just after the limiter is set. 161 */ 162 typedef int l_init_t(struct iop_stats *); 163 164 /* 165 * Called every tick. 166 */ 167 typedef int l_tick_t(struct iop_stats *); 168 169 /* 170 * Called to see if the limiter thinks this IOP can be allowed to 171 * proceed. If so, the limiter assumes that the IOP proceeded 172 * and makes any accounting of it that's needed. 173 */ 174 typedef int l_iop_t(struct iop_stats *, struct bio *); 175 176 /* 177 * Called when an I/O completes so the limiter can update its 178 * accounting. Pending I/Os may complete in any order (even when 179 * sent to the hardware at the same time), so the limiter may not 180 * make any assumptions other than this I/O has completed. If it 181 * returns 1, then xpt_schedule() needs to be called again. 182 */ 183 typedef int l_iodone_t(struct iop_stats *, struct bio *); 184 185 static l_iop_t cam_iosched_qd_iop; 186 static l_iop_t cam_iosched_qd_caniop; 187 static l_iodone_t cam_iosched_qd_iodone; 188 189 static l_init_t cam_iosched_iops_init; 190 static l_tick_t cam_iosched_iops_tick; 191 static l_iop_t cam_iosched_iops_caniop; 192 static l_iop_t cam_iosched_iops_iop; 193 194 static l_init_t cam_iosched_bw_init; 195 static l_tick_t cam_iosched_bw_tick; 196 static l_iop_t cam_iosched_bw_caniop; 197 static l_iop_t cam_iosched_bw_iop; 198 199 struct limswitch { 200 l_init_t *l_init; 201 l_tick_t *l_tick; 202 l_iop_t *l_iop; 203 l_iop_t *l_caniop; 204 l_iodone_t *l_iodone; 205 } limsw[] = 206 { 207 { /* none */ 208 .l_init = NULL, 209 .l_tick = NULL, 210 .l_iop = NULL, 211 .l_iodone= NULL, 212 }, 213 { /* queue_depth */ 214 .l_init = NULL, 215 .l_tick = NULL, 216 .l_caniop = cam_iosched_qd_caniop, 217 .l_iop = cam_iosched_qd_iop, 218 .l_iodone= cam_iosched_qd_iodone, 219 }, 220 { /* iops */ 221 .l_init = cam_iosched_iops_init, 222 .l_tick = cam_iosched_iops_tick, 223 .l_caniop = cam_iosched_iops_caniop, 224 .l_iop = cam_iosched_iops_iop, 225 .l_iodone= NULL, 226 }, 227 { /* bandwidth */ 228 .l_init = cam_iosched_bw_init, 229 .l_tick = cam_iosched_bw_tick, 230 .l_caniop = cam_iosched_bw_caniop, 231 .l_iop = cam_iosched_bw_iop, 232 .l_iodone= NULL, 233 }, 234 }; 235 236 struct iop_stats { 237 /* 238 * sysctl state for this subnode. 239 */ 240 struct sysctl_ctx_list sysctl_ctx; 241 struct sysctl_oid *sysctl_tree; 242 243 /* 244 * Information about the current rate limiters, if any 245 */ 246 io_limiter limiter; /* How are I/Os being limited */ 247 int min; /* Low range of limit */ 248 int max; /* High range of limit */ 249 int current; /* Current rate limiter */ 250 int l_value1; /* per-limiter scratch value 1. */ 251 int l_value2; /* per-limiter scratch value 2. */ 252 253 /* 254 * Debug information about counts of I/Os that have gone through the 255 * scheduler. 256 */ 257 int pending; /* I/Os pending in the hardware */ 258 int queued; /* number currently in the queue */ 259 int total; /* Total for all time -- wraps */ 260 int in; /* number queued all time -- wraps */ 261 int out; /* number completed all time -- wraps */ 262 int errs; /* Number of I/Os completed with error -- wraps */ 263 264 /* 265 * Statistics on different bits of the process. 266 */ 267 /* Exp Moving Average, see alpha_bits for more details */ 268 sbintime_t ema; 269 sbintime_t emvar; 270 sbintime_t sd; /* Last computed sd */ 271 272 uint32_t state_flags; 273 #define IOP_RATE_LIMITED 1u 274 275 uint64_t latencies[LAT_BUCKETS]; 276 277 struct cam_iosched_softc *softc; 278 }; 279 280 typedef enum { 281 set_max = 0, /* current = max */ 282 read_latency, /* Steer read latency by throttling writes */ 283 cl_max /* Keep last */ 284 } control_type; 285 286 static const char *cam_iosched_control_type_names[] = 287 { "set_max", "read_latency" }; 288 289 struct control_loop { 290 /* 291 * sysctl state for this subnode. 292 */ 293 struct sysctl_ctx_list sysctl_ctx; 294 struct sysctl_oid *sysctl_tree; 295 296 sbintime_t next_steer; /* Time of next steer */ 297 sbintime_t steer_interval; /* How often do we steer? */ 298 sbintime_t lolat; 299 sbintime_t hilat; 300 int alpha; 301 control_type type; /* What type of control? */ 302 int last_count; /* Last I/O count */ 303 304 struct cam_iosched_softc *softc; 305 }; 306 307 #endif 308 309 struct cam_iosched_softc { 310 struct bio_queue_head bio_queue; 311 struct bio_queue_head trim_queue; 312 /* scheduler flags < 16, user flags >= 16 */ 313 uint32_t flags; 314 int sort_io_queue; 315 int trim_goal; /* # of trims to queue before sending */ 316 int trim_ticks; /* Max ticks to hold trims */ 317 int last_trim_tick; /* Last 'tick' time ld a trim */ 318 int queued_trims; /* Number of trims in the queue */ 319 #ifdef CAM_IOSCHED_DYNAMIC 320 int read_bias; /* Read bias setting */ 321 int current_read_bias; /* Current read bias state */ 322 int total_ticks; 323 int load; /* EMA of 'load average' of disk / 2^16 */ 324 325 struct bio_queue_head write_queue; 326 struct iop_stats read_stats, write_stats, trim_stats; 327 struct sysctl_ctx_list sysctl_ctx; 328 struct sysctl_oid *sysctl_tree; 329 330 int quanta; /* Number of quanta per second */ 331 struct callout ticker; /* Callout for our quota system */ 332 struct cam_periph *periph; /* cam periph associated with this device */ 333 uint32_t this_frac; /* Fraction of a second (1024ths) for this tick */ 334 sbintime_t last_time; /* Last time we ticked */ 335 struct control_loop cl; 336 sbintime_t max_lat; /* when != 0, if iop latency > max_lat, call max_lat_fcn */ 337 cam_iosched_latfcn_t latfcn; 338 void *latarg; 339 #endif 340 }; 341 342 #ifdef CAM_IOSCHED_DYNAMIC 343 /* 344 * helper functions to call the limsw functions. 345 */ 346 static int 347 cam_iosched_limiter_init(struct iop_stats *ios) 348 { 349 int lim = ios->limiter; 350 351 /* maybe this should be a kassert */ 352 if (lim < none || lim >= limiter_max) 353 return EINVAL; 354 355 if (limsw[lim].l_init) 356 return limsw[lim].l_init(ios); 357 358 return 0; 359 } 360 361 static int 362 cam_iosched_limiter_tick(struct iop_stats *ios) 363 { 364 int lim = ios->limiter; 365 366 /* maybe this should be a kassert */ 367 if (lim < none || lim >= limiter_max) 368 return EINVAL; 369 370 if (limsw[lim].l_tick) 371 return limsw[lim].l_tick(ios); 372 373 return 0; 374 } 375 376 static int 377 cam_iosched_limiter_iop(struct iop_stats *ios, struct bio *bp) 378 { 379 int lim = ios->limiter; 380 381 /* maybe this should be a kassert */ 382 if (lim < none || lim >= limiter_max) 383 return EINVAL; 384 385 if (limsw[lim].l_iop) 386 return limsw[lim].l_iop(ios, bp); 387 388 return 0; 389 } 390 391 static int 392 cam_iosched_limiter_caniop(struct iop_stats *ios, struct bio *bp) 393 { 394 int lim = ios->limiter; 395 396 /* maybe this should be a kassert */ 397 if (lim < none || lim >= limiter_max) 398 return EINVAL; 399 400 if (limsw[lim].l_caniop) 401 return limsw[lim].l_caniop(ios, bp); 402 403 return 0; 404 } 405 406 static int 407 cam_iosched_limiter_iodone(struct iop_stats *ios, struct bio *bp) 408 { 409 int lim = ios->limiter; 410 411 /* maybe this should be a kassert */ 412 if (lim < none || lim >= limiter_max) 413 return 0; 414 415 if (limsw[lim].l_iodone) 416 return limsw[lim].l_iodone(ios, bp); 417 418 return 0; 419 } 420 421 /* 422 * Functions to implement the different kinds of limiters 423 */ 424 425 static int 426 cam_iosched_qd_iop(struct iop_stats *ios, struct bio *bp) 427 { 428 429 if (ios->current <= 0 || ios->pending < ios->current) 430 return 0; 431 432 return EAGAIN; 433 } 434 435 static int 436 cam_iosched_qd_caniop(struct iop_stats *ios, struct bio *bp) 437 { 438 439 if (ios->current <= 0 || ios->pending < ios->current) 440 return 0; 441 442 return EAGAIN; 443 } 444 445 static int 446 cam_iosched_qd_iodone(struct iop_stats *ios, struct bio *bp) 447 { 448 449 if (ios->current <= 0 || ios->pending != ios->current) 450 return 0; 451 452 return 1; 453 } 454 455 static int 456 cam_iosched_iops_init(struct iop_stats *ios) 457 { 458 459 ios->l_value1 = ios->current / ios->softc->quanta; 460 if (ios->l_value1 <= 0) 461 ios->l_value1 = 1; 462 ios->l_value2 = 0; 463 464 return 0; 465 } 466 467 static int 468 cam_iosched_iops_tick(struct iop_stats *ios) 469 { 470 int new_ios; 471 472 /* 473 * Allow at least one IO per tick until all 474 * the IOs for this interval have been spent. 475 */ 476 new_ios = (int)((ios->current * (uint64_t)ios->softc->this_frac) >> 16); 477 if (new_ios < 1 && ios->l_value2 < ios->current) { 478 new_ios = 1; 479 ios->l_value2++; 480 } 481 482 /* 483 * If this a new accounting interval, discard any "unspent" ios 484 * granted in the previous interval. Otherwise add the new ios to 485 * the previously granted ones that haven't been spent yet. 486 */ 487 if ((ios->softc->total_ticks % ios->softc->quanta) == 0) { 488 ios->l_value1 = new_ios; 489 ios->l_value2 = 1; 490 } else { 491 ios->l_value1 += new_ios; 492 } 493 494 return 0; 495 } 496 497 static int 498 cam_iosched_iops_caniop(struct iop_stats *ios, struct bio *bp) 499 { 500 501 /* 502 * So if we have any more IOPs left, allow it, 503 * otherwise wait. If current iops is 0, treat that 504 * as unlimited as a failsafe. 505 */ 506 if (ios->current > 0 && ios->l_value1 <= 0) 507 return EAGAIN; 508 return 0; 509 } 510 511 static int 512 cam_iosched_iops_iop(struct iop_stats *ios, struct bio *bp) 513 { 514 int rv; 515 516 rv = cam_iosched_limiter_caniop(ios, bp); 517 if (rv == 0) 518 ios->l_value1--; 519 520 return rv; 521 } 522 523 static int 524 cam_iosched_bw_init(struct iop_stats *ios) 525 { 526 527 /* ios->current is in kB/s, so scale to bytes */ 528 ios->l_value1 = ios->current * 1000 / ios->softc->quanta; 529 530 return 0; 531 } 532 533 static int 534 cam_iosched_bw_tick(struct iop_stats *ios) 535 { 536 int bw; 537 538 /* 539 * If we're in the hole for available quota from 540 * the last time, then add the quantum for this. 541 * If we have any left over from last quantum, 542 * then too bad, that's lost. Also, ios->current 543 * is in kB/s, so scale. 544 * 545 * We also allow up to 4 quanta of credits to 546 * accumulate to deal with burstiness. 4 is extremely 547 * arbitrary. 548 */ 549 bw = (int)((ios->current * 1000ull * (uint64_t)ios->softc->this_frac) >> 16); 550 if (ios->l_value1 < bw * 4) 551 ios->l_value1 += bw; 552 553 return 0; 554 } 555 556 static int 557 cam_iosched_bw_caniop(struct iop_stats *ios, struct bio *bp) 558 { 559 /* 560 * So if we have any more bw quota left, allow it, 561 * otherwise wait. Note, we'll go negative and that's 562 * OK. We'll just get a little less next quota. 563 * 564 * Note on going negative: that allows us to process 565 * requests in order better, since we won't allow 566 * shorter reads to get around the long one that we 567 * don't have the quota to do just yet. It also prevents 568 * starvation by being a little more permissive about 569 * what we let through this quantum (to prevent the 570 * starvation), at the cost of getting a little less 571 * next quantum. 572 * 573 * Also note that if the current limit is <= 0, 574 * we treat it as unlimited as a failsafe. 575 */ 576 if (ios->current > 0 && ios->l_value1 <= 0) 577 return EAGAIN; 578 579 return 0; 580 } 581 582 static int 583 cam_iosched_bw_iop(struct iop_stats *ios, struct bio *bp) 584 { 585 int rv; 586 587 rv = cam_iosched_limiter_caniop(ios, bp); 588 if (rv == 0) 589 ios->l_value1 -= bp->bio_length; 590 591 return rv; 592 } 593 594 static void cam_iosched_cl_maybe_steer(struct control_loop *clp); 595 596 static void 597 cam_iosched_ticker(void *arg) 598 { 599 struct cam_iosched_softc *isc = arg; 600 sbintime_t now, delta; 601 int pending; 602 603 callout_reset(&isc->ticker, hz / isc->quanta, cam_iosched_ticker, isc); 604 605 now = sbinuptime(); 606 delta = now - isc->last_time; 607 isc->this_frac = (uint32_t)delta >> 16; /* Note: discards seconds -- should be 0 harmless if not */ 608 isc->last_time = now; 609 610 cam_iosched_cl_maybe_steer(&isc->cl); 611 612 cam_iosched_limiter_tick(&isc->read_stats); 613 cam_iosched_limiter_tick(&isc->write_stats); 614 cam_iosched_limiter_tick(&isc->trim_stats); 615 616 cam_iosched_schedule(isc, isc->periph); 617 618 /* 619 * isc->load is an EMA of the pending I/Os at each tick. The number of 620 * pending I/Os is the sum of the I/Os queued to the hardware, and those 621 * in the software queue that could be queued to the hardware if there 622 * were slots. 623 * 624 * ios_stats.pending is a count of requests in the SIM right now for 625 * each of these types of I/O. So the total pending count is the sum of 626 * these I/Os and the sum of the queued I/Os still in the software queue 627 * for those operations that aren't being rate limited at the moment. 628 * 629 * The reason for the rate limiting bit is because those I/Os 630 * aren't part of the software queued load (since we could 631 * give them to hardware, but choose not to). 632 * 633 * Note: due to a bug in counting pending TRIM in the device, we 634 * don't include them in this count. We count each BIO_DELETE in 635 * the pending count, but the periph drivers collapse them down 636 * into one TRIM command. That one trim command gets the completion 637 * so the counts get off. 638 */ 639 pending = isc->read_stats.pending + isc->write_stats.pending /* + isc->trim_stats.pending */; 640 pending += !!(isc->read_stats.state_flags & IOP_RATE_LIMITED) * isc->read_stats.queued + 641 !!(isc->write_stats.state_flags & IOP_RATE_LIMITED) * isc->write_stats.queued /* + 642 !!(isc->trim_stats.state_flags & IOP_RATE_LIMITED) * isc->trim_stats.queued */ ; 643 pending <<= 16; 644 pending /= isc->periph->path->device->ccbq.total_openings; 645 646 isc->load = (pending + (isc->load << 13) - isc->load) >> 13; /* see above: 13 -> 16139 / 200/s = ~81s ~1 minute */ 647 648 isc->total_ticks++; 649 } 650 651 static void 652 cam_iosched_cl_init(struct control_loop *clp, struct cam_iosched_softc *isc) 653 { 654 655 clp->next_steer = sbinuptime(); 656 clp->softc = isc; 657 clp->steer_interval = SBT_1S * 5; /* Let's start out steering every 5s */ 658 clp->lolat = 5 * SBT_1MS; 659 clp->hilat = 15 * SBT_1MS; 660 clp->alpha = 20; /* Alpha == gain. 20 = .2 */ 661 clp->type = set_max; 662 } 663 664 static void 665 cam_iosched_cl_maybe_steer(struct control_loop *clp) 666 { 667 struct cam_iosched_softc *isc; 668 sbintime_t now, lat; 669 int old; 670 671 isc = clp->softc; 672 now = isc->last_time; 673 if (now < clp->next_steer) 674 return; 675 676 clp->next_steer = now + clp->steer_interval; 677 switch (clp->type) { 678 case set_max: 679 if (isc->write_stats.current != isc->write_stats.max) 680 printf("Steering write from %d kBps to %d kBps\n", 681 isc->write_stats.current, isc->write_stats.max); 682 isc->read_stats.current = isc->read_stats.max; 683 isc->write_stats.current = isc->write_stats.max; 684 isc->trim_stats.current = isc->trim_stats.max; 685 break; 686 case read_latency: 687 old = isc->write_stats.current; 688 lat = isc->read_stats.ema; 689 /* 690 * Simple PLL-like engine. Since we're steering to a range for 691 * the SP (set point) that makes things a little more 692 * complicated. In addition, we're not directly controlling our 693 * PV (process variable), the read latency, but instead are 694 * manipulating the write bandwidth limit for our MV 695 * (manipulation variable), analysis of this code gets a bit 696 * messy. Also, the MV is a very noisy control surface for read 697 * latency since it is affected by many hidden processes inside 698 * the device which change how responsive read latency will be 699 * in reaction to changes in write bandwidth. Unlike the classic 700 * boiler control PLL. this may result in over-steering while 701 * the SSD takes its time to react to the new, lower load. This 702 * is why we use a relatively low alpha of between .1 and .25 to 703 * compensate for this effect. At .1, it takes ~22 steering 704 * intervals to back off by a factor of 10. At .2 it only takes 705 * ~10. At .25 it only takes ~8. However some preliminary data 706 * from the SSD drives suggests a reasponse time in 10's of 707 * seconds before latency drops regardless of the new write 708 * rate. Careful observation will be required to tune this 709 * effectively. 710 * 711 * Also, when there's no read traffic, we jack up the write 712 * limit too regardless of the last read latency. 10 is 713 * somewhat arbitrary. 714 */ 715 if (lat < clp->lolat || isc->read_stats.total - clp->last_count < 10) 716 isc->write_stats.current = isc->write_stats.current * 717 (100 + clp->alpha) / 100; /* Scale up */ 718 else if (lat > clp->hilat) 719 isc->write_stats.current = isc->write_stats.current * 720 (100 - clp->alpha) / 100; /* Scale down */ 721 clp->last_count = isc->read_stats.total; 722 723 /* 724 * Even if we don't steer, per se, enforce the min/max limits as 725 * those may have changed. 726 */ 727 if (isc->write_stats.current < isc->write_stats.min) 728 isc->write_stats.current = isc->write_stats.min; 729 if (isc->write_stats.current > isc->write_stats.max) 730 isc->write_stats.current = isc->write_stats.max; 731 if (old != isc->write_stats.current && iosched_debug) 732 printf("Steering write from %d kBps to %d kBps due to latency of %jdus\n", 733 old, isc->write_stats.current, 734 (uintmax_t)((uint64_t)1000000 * (uint32_t)lat) >> 32); 735 break; 736 case cl_max: 737 break; 738 } 739 } 740 #endif 741 742 /* 743 * Trim or similar currently pending completion. Should only be set for 744 * those drivers wishing only one Trim active at a time. 745 */ 746 #define CAM_IOSCHED_FLAG_TRIM_ACTIVE (1ul << 0) 747 /* Callout active, and needs to be torn down */ 748 #define CAM_IOSCHED_FLAG_CALLOUT_ACTIVE (1ul << 1) 749 750 /* Periph drivers set these flags to indicate work */ 751 #define CAM_IOSCHED_FLAG_WORK_FLAGS ((0xffffu) << 16) 752 753 #ifdef CAM_IOSCHED_DYNAMIC 754 static void 755 cam_iosched_io_metric_update(struct cam_iosched_softc *isc, 756 sbintime_t sim_latency, int cmd, size_t size); 757 #endif 758 759 static inline bool 760 cam_iosched_has_flagged_work(struct cam_iosched_softc *isc) 761 { 762 return !!(isc->flags & CAM_IOSCHED_FLAG_WORK_FLAGS); 763 } 764 765 static inline bool 766 cam_iosched_has_io(struct cam_iosched_softc *isc) 767 { 768 #ifdef CAM_IOSCHED_DYNAMIC 769 if (do_dynamic_iosched) { 770 struct bio *rbp = bioq_first(&isc->bio_queue); 771 struct bio *wbp = bioq_first(&isc->write_queue); 772 bool can_write = wbp != NULL && 773 cam_iosched_limiter_caniop(&isc->write_stats, wbp) == 0; 774 bool can_read = rbp != NULL && 775 cam_iosched_limiter_caniop(&isc->read_stats, rbp) == 0; 776 if (iosched_debug > 2) { 777 printf("can write %d: pending_writes %d max_writes %d\n", can_write, isc->write_stats.pending, isc->write_stats.max); 778 printf("can read %d: read_stats.pending %d max_reads %d\n", can_read, isc->read_stats.pending, isc->read_stats.max); 779 printf("Queued reads %d writes %d\n", isc->read_stats.queued, isc->write_stats.queued); 780 } 781 return can_read || can_write; 782 } 783 #endif 784 return bioq_first(&isc->bio_queue) != NULL; 785 } 786 787 static inline bool 788 cam_iosched_has_more_trim(struct cam_iosched_softc *isc) 789 { 790 struct bio *bp; 791 792 bp = bioq_first(&isc->trim_queue); 793 #ifdef CAM_IOSCHED_DYNAMIC 794 if (do_dynamic_iosched) { 795 /* 796 * If we're limiting trims, then defer action on trims 797 * for a bit. 798 */ 799 if (bp == NULL || cam_iosched_limiter_caniop(&isc->trim_stats, bp) != 0) 800 return false; 801 } 802 #endif 803 804 /* 805 * If we've set a trim_goal, then if we exceed that allow trims 806 * to be passed back to the driver. If we've also set a tick timeout 807 * allow trims back to the driver. Otherwise, don't allow trims yet. 808 */ 809 if (isc->trim_goal > 0) { 810 if (isc->queued_trims >= isc->trim_goal) 811 return true; 812 if (isc->queued_trims > 0 && 813 isc->trim_ticks > 0 && 814 ticks - isc->last_trim_tick > isc->trim_ticks) 815 return true; 816 return false; 817 } 818 819 /* NB: Should perhaps have a max trim active independent of I/O limiters */ 820 return !(isc->flags & CAM_IOSCHED_FLAG_TRIM_ACTIVE) && bp != NULL; 821 } 822 823 #define cam_iosched_sort_queue(isc) ((isc)->sort_io_queue >= 0 ? \ 824 (isc)->sort_io_queue : cam_sort_io_queues) 825 826 static inline bool 827 cam_iosched_has_work(struct cam_iosched_softc *isc) 828 { 829 #ifdef CAM_IOSCHED_DYNAMIC 830 if (iosched_debug > 2) 831 printf("has work: %d %d %d\n", cam_iosched_has_io(isc), 832 cam_iosched_has_more_trim(isc), 833 cam_iosched_has_flagged_work(isc)); 834 #endif 835 836 return cam_iosched_has_io(isc) || 837 cam_iosched_has_more_trim(isc) || 838 cam_iosched_has_flagged_work(isc); 839 } 840 841 #ifdef CAM_IOSCHED_DYNAMIC 842 static void 843 cam_iosched_iop_stats_init(struct cam_iosched_softc *isc, struct iop_stats *ios) 844 { 845 846 ios->limiter = none; 847 ios->in = 0; 848 ios->max = ios->current = 300000; 849 ios->min = 1; 850 ios->out = 0; 851 ios->errs = 0; 852 ios->pending = 0; 853 ios->queued = 0; 854 ios->total = 0; 855 ios->ema = 0; 856 ios->emvar = 0; 857 ios->softc = isc; 858 cam_iosched_limiter_init(ios); 859 } 860 861 static int 862 cam_iosched_limiter_sysctl(SYSCTL_HANDLER_ARGS) 863 { 864 char buf[16]; 865 struct iop_stats *ios; 866 struct cam_iosched_softc *isc; 867 int value, i, error; 868 const char *p; 869 870 ios = arg1; 871 isc = ios->softc; 872 value = ios->limiter; 873 if (value < none || value >= limiter_max) 874 p = "UNKNOWN"; 875 else 876 p = cam_iosched_limiter_names[value]; 877 878 strlcpy(buf, p, sizeof(buf)); 879 error = sysctl_handle_string(oidp, buf, sizeof(buf), req); 880 if (error != 0 || req->newptr == NULL) 881 return error; 882 883 cam_periph_lock(isc->periph); 884 885 for (i = none; i < limiter_max; i++) { 886 if (strcmp(buf, cam_iosched_limiter_names[i]) != 0) 887 continue; 888 ios->limiter = i; 889 error = cam_iosched_limiter_init(ios); 890 if (error != 0) { 891 ios->limiter = value; 892 cam_periph_unlock(isc->periph); 893 return error; 894 } 895 /* Note: disk load averate requires ticker to be always running */ 896 callout_reset(&isc->ticker, hz / isc->quanta, cam_iosched_ticker, isc); 897 isc->flags |= CAM_IOSCHED_FLAG_CALLOUT_ACTIVE; 898 899 cam_periph_unlock(isc->periph); 900 return 0; 901 } 902 903 cam_periph_unlock(isc->periph); 904 return EINVAL; 905 } 906 907 static int 908 cam_iosched_control_type_sysctl(SYSCTL_HANDLER_ARGS) 909 { 910 char buf[16]; 911 struct control_loop *clp; 912 struct cam_iosched_softc *isc; 913 int value, i, error; 914 const char *p; 915 916 clp = arg1; 917 isc = clp->softc; 918 value = clp->type; 919 if (value < none || value >= cl_max) 920 p = "UNKNOWN"; 921 else 922 p = cam_iosched_control_type_names[value]; 923 924 strlcpy(buf, p, sizeof(buf)); 925 error = sysctl_handle_string(oidp, buf, sizeof(buf), req); 926 if (error != 0 || req->newptr == NULL) 927 return error; 928 929 for (i = set_max; i < cl_max; i++) { 930 if (strcmp(buf, cam_iosched_control_type_names[i]) != 0) 931 continue; 932 cam_periph_lock(isc->periph); 933 clp->type = i; 934 cam_periph_unlock(isc->periph); 935 return 0; 936 } 937 938 return EINVAL; 939 } 940 941 static int 942 cam_iosched_sbintime_sysctl(SYSCTL_HANDLER_ARGS) 943 { 944 char buf[16]; 945 sbintime_t value; 946 int error; 947 uint64_t us; 948 949 value = *(sbintime_t *)arg1; 950 us = (uint64_t)value / SBT_1US; 951 snprintf(buf, sizeof(buf), "%ju", (intmax_t)us); 952 error = sysctl_handle_string(oidp, buf, sizeof(buf), req); 953 if (error != 0 || req->newptr == NULL) 954 return error; 955 us = strtoul(buf, NULL, 10); 956 if (us == 0) 957 return EINVAL; 958 *(sbintime_t *)arg1 = us * SBT_1US; 959 return 0; 960 } 961 962 static int 963 cam_iosched_sysctl_latencies(SYSCTL_HANDLER_ARGS) 964 { 965 int i, error; 966 struct sbuf sb; 967 uint64_t *latencies; 968 969 latencies = arg1; 970 sbuf_new_for_sysctl(&sb, NULL, LAT_BUCKETS * 16, req); 971 972 for (i = 0; i < LAT_BUCKETS - 1; i++) 973 sbuf_printf(&sb, "%jd,", (intmax_t)latencies[i]); 974 sbuf_printf(&sb, "%jd", (intmax_t)latencies[LAT_BUCKETS - 1]); 975 error = sbuf_finish(&sb); 976 sbuf_delete(&sb); 977 978 return (error); 979 } 980 981 static int 982 cam_iosched_quanta_sysctl(SYSCTL_HANDLER_ARGS) 983 { 984 int *quanta; 985 int error, value; 986 987 quanta = (unsigned *)arg1; 988 value = *quanta; 989 990 error = sysctl_handle_int(oidp, (int *)&value, 0, req); 991 if ((error != 0) || (req->newptr == NULL)) 992 return (error); 993 994 if (value < 1 || value > hz) 995 return (EINVAL); 996 997 *quanta = value; 998 999 return (0); 1000 } 1001 1002 static void 1003 cam_iosched_iop_stats_sysctl_init(struct cam_iosched_softc *isc, struct iop_stats *ios, char *name) 1004 { 1005 struct sysctl_oid_list *n; 1006 struct sysctl_ctx_list *ctx; 1007 1008 ios->sysctl_tree = SYSCTL_ADD_NODE(&isc->sysctl_ctx, 1009 SYSCTL_CHILDREN(isc->sysctl_tree), OID_AUTO, name, 1010 CTLFLAG_RD | CTLFLAG_MPSAFE, 0, name); 1011 n = SYSCTL_CHILDREN(ios->sysctl_tree); 1012 ctx = &ios->sysctl_ctx; 1013 1014 SYSCTL_ADD_UQUAD(ctx, n, 1015 OID_AUTO, "ema", CTLFLAG_RD, 1016 &ios->ema, 1017 "Fast Exponentially Weighted Moving Average"); 1018 SYSCTL_ADD_UQUAD(ctx, n, 1019 OID_AUTO, "emvar", CTLFLAG_RD, 1020 &ios->emvar, 1021 "Fast Exponentially Weighted Moving Variance"); 1022 1023 SYSCTL_ADD_INT(ctx, n, 1024 OID_AUTO, "pending", CTLFLAG_RD, 1025 &ios->pending, 0, 1026 "Instantaneous # of pending transactions"); 1027 SYSCTL_ADD_INT(ctx, n, 1028 OID_AUTO, "count", CTLFLAG_RD, 1029 &ios->total, 0, 1030 "# of transactions submitted to hardware"); 1031 SYSCTL_ADD_INT(ctx, n, 1032 OID_AUTO, "queued", CTLFLAG_RD, 1033 &ios->queued, 0, 1034 "# of transactions in the queue"); 1035 SYSCTL_ADD_INT(ctx, n, 1036 OID_AUTO, "in", CTLFLAG_RD, 1037 &ios->in, 0, 1038 "# of transactions queued to driver"); 1039 SYSCTL_ADD_INT(ctx, n, 1040 OID_AUTO, "out", CTLFLAG_RD, 1041 &ios->out, 0, 1042 "# of transactions completed (including with error)"); 1043 SYSCTL_ADD_INT(ctx, n, 1044 OID_AUTO, "errs", CTLFLAG_RD, 1045 &ios->errs, 0, 1046 "# of transactions completed with an error"); 1047 1048 SYSCTL_ADD_PROC(ctx, n, 1049 OID_AUTO, "limiter", 1050 CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_MPSAFE, 1051 ios, 0, cam_iosched_limiter_sysctl, "A", 1052 "Current limiting type."); 1053 SYSCTL_ADD_INT(ctx, n, 1054 OID_AUTO, "min", CTLFLAG_RW, 1055 &ios->min, 0, 1056 "min resource"); 1057 SYSCTL_ADD_INT(ctx, n, 1058 OID_AUTO, "max", CTLFLAG_RW, 1059 &ios->max, 0, 1060 "max resource"); 1061 SYSCTL_ADD_INT(ctx, n, 1062 OID_AUTO, "current", CTLFLAG_RW, 1063 &ios->current, 0, 1064 "current resource"); 1065 1066 SYSCTL_ADD_PROC(ctx, n, 1067 OID_AUTO, "latencies", 1068 CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MPSAFE, 1069 &ios->latencies, 0, 1070 cam_iosched_sysctl_latencies, "A", 1071 "Array of power of 2 latency from 1ms to 1.024s"); 1072 } 1073 1074 static void 1075 cam_iosched_iop_stats_fini(struct iop_stats *ios) 1076 { 1077 if (ios->sysctl_tree) 1078 if (sysctl_ctx_free(&ios->sysctl_ctx) != 0) 1079 printf("can't remove iosched sysctl stats context\n"); 1080 } 1081 1082 static void 1083 cam_iosched_cl_sysctl_init(struct cam_iosched_softc *isc) 1084 { 1085 struct sysctl_oid_list *n; 1086 struct sysctl_ctx_list *ctx; 1087 struct control_loop *clp; 1088 1089 clp = &isc->cl; 1090 clp->sysctl_tree = SYSCTL_ADD_NODE(&isc->sysctl_ctx, 1091 SYSCTL_CHILDREN(isc->sysctl_tree), OID_AUTO, "control", 1092 CTLFLAG_RD | CTLFLAG_MPSAFE, 0, "Control loop info"); 1093 n = SYSCTL_CHILDREN(clp->sysctl_tree); 1094 ctx = &clp->sysctl_ctx; 1095 1096 SYSCTL_ADD_PROC(ctx, n, 1097 OID_AUTO, "type", 1098 CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_MPSAFE, 1099 clp, 0, cam_iosched_control_type_sysctl, "A", 1100 "Control loop algorithm"); 1101 SYSCTL_ADD_PROC(ctx, n, 1102 OID_AUTO, "steer_interval", 1103 CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_MPSAFE, 1104 &clp->steer_interval, 0, cam_iosched_sbintime_sysctl, "A", 1105 "How often to steer (in us)"); 1106 SYSCTL_ADD_PROC(ctx, n, 1107 OID_AUTO, "lolat", 1108 CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_MPSAFE, 1109 &clp->lolat, 0, cam_iosched_sbintime_sysctl, "A", 1110 "Low water mark for Latency (in us)"); 1111 SYSCTL_ADD_PROC(ctx, n, 1112 OID_AUTO, "hilat", 1113 CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_MPSAFE, 1114 &clp->hilat, 0, cam_iosched_sbintime_sysctl, "A", 1115 "Hi water mark for Latency (in us)"); 1116 SYSCTL_ADD_INT(ctx, n, 1117 OID_AUTO, "alpha", CTLFLAG_RW, 1118 &clp->alpha, 0, 1119 "Alpha for PLL (x100) aka gain"); 1120 } 1121 1122 static void 1123 cam_iosched_cl_sysctl_fini(struct control_loop *clp) 1124 { 1125 if (clp->sysctl_tree) 1126 if (sysctl_ctx_free(&clp->sysctl_ctx) != 0) 1127 printf("can't remove iosched sysctl control loop context\n"); 1128 } 1129 #endif 1130 1131 /* 1132 * Allocate the iosched structure. This also insulates callers from knowing 1133 * sizeof struct cam_iosched_softc. 1134 */ 1135 int 1136 cam_iosched_init(struct cam_iosched_softc **iscp, struct cam_periph *periph) 1137 { 1138 1139 *iscp = malloc(sizeof(**iscp), M_CAMSCHED, M_NOWAIT | M_ZERO); 1140 if (*iscp == NULL) 1141 return ENOMEM; 1142 #ifdef CAM_IOSCHED_DYNAMIC 1143 if (iosched_debug) 1144 printf("CAM IOSCHEDULER Allocating entry at %p\n", *iscp); 1145 #endif 1146 (*iscp)->sort_io_queue = -1; 1147 bioq_init(&(*iscp)->bio_queue); 1148 bioq_init(&(*iscp)->trim_queue); 1149 #ifdef CAM_IOSCHED_DYNAMIC 1150 if (do_dynamic_iosched) { 1151 bioq_init(&(*iscp)->write_queue); 1152 (*iscp)->read_bias = 100; 1153 (*iscp)->current_read_bias = 100; 1154 (*iscp)->quanta = min(hz, 200); 1155 cam_iosched_iop_stats_init(*iscp, &(*iscp)->read_stats); 1156 cam_iosched_iop_stats_init(*iscp, &(*iscp)->write_stats); 1157 cam_iosched_iop_stats_init(*iscp, &(*iscp)->trim_stats); 1158 (*iscp)->trim_stats.max = 1; /* Trims are special: one at a time for now */ 1159 (*iscp)->last_time = sbinuptime(); 1160 callout_init_mtx(&(*iscp)->ticker, cam_periph_mtx(periph), 0); 1161 (*iscp)->periph = periph; 1162 cam_iosched_cl_init(&(*iscp)->cl, *iscp); 1163 callout_reset(&(*iscp)->ticker, hz / (*iscp)->quanta, cam_iosched_ticker, *iscp); 1164 (*iscp)->flags |= CAM_IOSCHED_FLAG_CALLOUT_ACTIVE; 1165 } 1166 #endif 1167 1168 return 0; 1169 } 1170 1171 /* 1172 * Reclaim all used resources. This assumes that other folks have 1173 * drained the requests in the hardware. Maybe an unwise assumption. 1174 */ 1175 void 1176 cam_iosched_fini(struct cam_iosched_softc *isc) 1177 { 1178 if (isc) { 1179 cam_iosched_flush(isc, NULL, ENXIO); 1180 #ifdef CAM_IOSCHED_DYNAMIC 1181 cam_iosched_iop_stats_fini(&isc->read_stats); 1182 cam_iosched_iop_stats_fini(&isc->write_stats); 1183 cam_iosched_iop_stats_fini(&isc->trim_stats); 1184 cam_iosched_cl_sysctl_fini(&isc->cl); 1185 if (isc->sysctl_tree) 1186 if (sysctl_ctx_free(&isc->sysctl_ctx) != 0) 1187 printf("can't remove iosched sysctl stats context\n"); 1188 if (isc->flags & CAM_IOSCHED_FLAG_CALLOUT_ACTIVE) { 1189 callout_drain(&isc->ticker); 1190 isc->flags &= ~ CAM_IOSCHED_FLAG_CALLOUT_ACTIVE; 1191 } 1192 #endif 1193 free(isc, M_CAMSCHED); 1194 } 1195 } 1196 1197 /* 1198 * After we're sure we're attaching a device, go ahead and add 1199 * hooks for any sysctl we may wish to honor. 1200 */ 1201 void cam_iosched_sysctl_init(struct cam_iosched_softc *isc, 1202 struct sysctl_ctx_list *ctx, struct sysctl_oid *node) 1203 { 1204 struct sysctl_oid_list *n; 1205 1206 n = SYSCTL_CHILDREN(node); 1207 SYSCTL_ADD_INT(ctx, n, 1208 OID_AUTO, "sort_io_queue", CTLFLAG_RW | CTLFLAG_MPSAFE, 1209 &isc->sort_io_queue, 0, 1210 "Sort IO queue to try and optimise disk access patterns"); 1211 SYSCTL_ADD_INT(ctx, n, 1212 OID_AUTO, "trim_goal", CTLFLAG_RW, 1213 &isc->trim_goal, 0, 1214 "Number of trims to try to accumulate before sending to hardware"); 1215 SYSCTL_ADD_INT(ctx, n, 1216 OID_AUTO, "trim_ticks", CTLFLAG_RW, 1217 &isc->trim_goal, 0, 1218 "IO Schedul qaunta to hold back trims for when accumulating"); 1219 1220 #ifdef CAM_IOSCHED_DYNAMIC 1221 if (!do_dynamic_iosched) 1222 return; 1223 1224 isc->sysctl_tree = SYSCTL_ADD_NODE(&isc->sysctl_ctx, 1225 SYSCTL_CHILDREN(node), OID_AUTO, "iosched", 1226 CTLFLAG_RD | CTLFLAG_MPSAFE, 0, "I/O scheduler statistics"); 1227 n = SYSCTL_CHILDREN(isc->sysctl_tree); 1228 ctx = &isc->sysctl_ctx; 1229 1230 cam_iosched_iop_stats_sysctl_init(isc, &isc->read_stats, "read"); 1231 cam_iosched_iop_stats_sysctl_init(isc, &isc->write_stats, "write"); 1232 cam_iosched_iop_stats_sysctl_init(isc, &isc->trim_stats, "trim"); 1233 cam_iosched_cl_sysctl_init(isc); 1234 1235 SYSCTL_ADD_INT(ctx, n, 1236 OID_AUTO, "read_bias", CTLFLAG_RW, 1237 &isc->read_bias, 100, 1238 "How biased towards read should we be independent of limits"); 1239 1240 SYSCTL_ADD_PROC(ctx, n, 1241 OID_AUTO, "quanta", CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_MPSAFE, 1242 &isc->quanta, 0, cam_iosched_quanta_sysctl, "I", 1243 "How many quanta per second do we slice the I/O up into"); 1244 1245 SYSCTL_ADD_INT(ctx, n, 1246 OID_AUTO, "total_ticks", CTLFLAG_RD, 1247 &isc->total_ticks, 0, 1248 "Total number of ticks we've done"); 1249 1250 SYSCTL_ADD_INT(ctx, n, 1251 OID_AUTO, "load", CTLFLAG_RD, 1252 &isc->load, 0, 1253 "scaled load average / 100"); 1254 1255 SYSCTL_ADD_U64(ctx, n, 1256 OID_AUTO, "latency_trigger", CTLFLAG_RW, 1257 &isc->max_lat, 0, 1258 "Latency treshold to trigger callbacks"); 1259 #endif 1260 } 1261 1262 void 1263 cam_iosched_set_latfcn(struct cam_iosched_softc *isc, 1264 cam_iosched_latfcn_t fnp, void *argp) 1265 { 1266 #ifdef CAM_IOSCHED_DYNAMIC 1267 isc->latfcn = fnp; 1268 isc->latarg = argp; 1269 #endif 1270 } 1271 1272 /* 1273 * Client drivers can set two parameters. "goal" is the number of BIO_DELETEs 1274 * that will be queued up before iosched will "release" the trims to the client 1275 * driver to wo with what they will (usually combine as many as possible). If we 1276 * don't get this many, after trim_ticks we'll submit the I/O anyway with 1277 * whatever we have. We do need an I/O of some kind of to clock the deferred 1278 * trims out to disk. Since we will eventually get a write for the super block 1279 * or something before we shutdown, the trims will complete. To be safe, when a 1280 * BIO_FLUSH is presented to the iosched work queue, we set the ticks time far 1281 * enough in the past so we'll present the BIO_DELETEs to the client driver. 1282 * There might be a race if no BIO_DELETESs were queued, a BIO_FLUSH comes in 1283 * and then a BIO_DELETE is sent down. No know client does this, and there's 1284 * already a race between an ordered BIO_FLUSH and any BIO_DELETEs in flight, 1285 * but no client depends on the ordering being honored. 1286 * 1287 * XXX I'm not sure what the interaction between UFS direct BIOs and the BUF 1288 * flushing on shutdown. I think there's bufs that would be dependent on the BIO 1289 * finishing to write out at least metadata, so we'll be fine. To be safe, keep 1290 * the number of ticks low (less than maybe 10s) to avoid shutdown races. 1291 */ 1292 1293 void 1294 cam_iosched_set_trim_goal(struct cam_iosched_softc *isc, int goal) 1295 { 1296 1297 isc->trim_goal = goal; 1298 } 1299 1300 void 1301 cam_iosched_set_trim_ticks(struct cam_iosched_softc *isc, int trim_ticks) 1302 { 1303 1304 isc->trim_ticks = trim_ticks; 1305 } 1306 1307 /* 1308 * Flush outstanding I/O. Consumers of this library don't know all the 1309 * queues we may keep, so this allows all I/O to be flushed in one 1310 * convenient call. 1311 */ 1312 void 1313 cam_iosched_flush(struct cam_iosched_softc *isc, struct devstat *stp, int err) 1314 { 1315 bioq_flush(&isc->bio_queue, stp, err); 1316 bioq_flush(&isc->trim_queue, stp, err); 1317 #ifdef CAM_IOSCHED_DYNAMIC 1318 if (do_dynamic_iosched) 1319 bioq_flush(&isc->write_queue, stp, err); 1320 #endif 1321 } 1322 1323 #ifdef CAM_IOSCHED_DYNAMIC 1324 static struct bio * 1325 cam_iosched_get_write(struct cam_iosched_softc *isc) 1326 { 1327 struct bio *bp; 1328 1329 /* 1330 * We control the write rate by controlling how many requests we send 1331 * down to the drive at any one time. Fewer requests limits the 1332 * effects of both starvation when the requests take a while and write 1333 * amplification when each request is causing more than one write to 1334 * the NAND media. Limiting the queue depth like this will also limit 1335 * the write throughput and give and reads that want to compete to 1336 * compete unfairly. 1337 */ 1338 bp = bioq_first(&isc->write_queue); 1339 if (bp == NULL) { 1340 if (iosched_debug > 3) 1341 printf("No writes present in write_queue\n"); 1342 return NULL; 1343 } 1344 1345 /* 1346 * If pending read, prefer that based on current read bias 1347 * setting. 1348 */ 1349 if (bioq_first(&isc->bio_queue) && isc->current_read_bias) { 1350 if (iosched_debug) 1351 printf( 1352 "Reads present and current_read_bias is %d queued " 1353 "writes %d queued reads %d\n", 1354 isc->current_read_bias, isc->write_stats.queued, 1355 isc->read_stats.queued); 1356 isc->current_read_bias--; 1357 /* We're not limiting writes, per se, just doing reads first */ 1358 return NULL; 1359 } 1360 1361 /* 1362 * See if our current limiter allows this I/O. 1363 */ 1364 if (cam_iosched_limiter_iop(&isc->write_stats, bp) != 0) { 1365 if (iosched_debug) 1366 printf("Can't write because limiter says no.\n"); 1367 isc->write_stats.state_flags |= IOP_RATE_LIMITED; 1368 return NULL; 1369 } 1370 1371 /* 1372 * Let's do this: We've passed all the gates and we're a go 1373 * to schedule the I/O in the SIM. 1374 */ 1375 isc->current_read_bias = isc->read_bias; 1376 bioq_remove(&isc->write_queue, bp); 1377 if (bp->bio_cmd == BIO_WRITE) { 1378 isc->write_stats.queued--; 1379 isc->write_stats.total++; 1380 isc->write_stats.pending++; 1381 } 1382 if (iosched_debug > 9) 1383 printf("HWQ : %p %#x\n", bp, bp->bio_cmd); 1384 isc->write_stats.state_flags &= ~IOP_RATE_LIMITED; 1385 return bp; 1386 } 1387 #endif 1388 1389 /* 1390 * Put back a trim that you weren't able to actually schedule this time. 1391 */ 1392 void 1393 cam_iosched_put_back_trim(struct cam_iosched_softc *isc, struct bio *bp) 1394 { 1395 bioq_insert_head(&isc->trim_queue, bp); 1396 if (isc->queued_trims == 0) 1397 isc->last_trim_tick = ticks; 1398 isc->queued_trims++; 1399 #ifdef CAM_IOSCHED_DYNAMIC 1400 isc->trim_stats.queued++; 1401 isc->trim_stats.total--; /* since we put it back, don't double count */ 1402 isc->trim_stats.pending--; 1403 #endif 1404 } 1405 1406 /* 1407 * gets the next trim from the trim queue. 1408 * 1409 * Assumes we're called with the periph lock held. It removes this 1410 * trim from the queue and the device must explicitly reinsert it 1411 * should the need arise. 1412 */ 1413 struct bio * 1414 cam_iosched_next_trim(struct cam_iosched_softc *isc) 1415 { 1416 struct bio *bp; 1417 1418 bp = bioq_first(&isc->trim_queue); 1419 if (bp == NULL) 1420 return NULL; 1421 bioq_remove(&isc->trim_queue, bp); 1422 isc->queued_trims--; 1423 isc->last_trim_tick = ticks; /* Reset the tick timer when we take trims */ 1424 #ifdef CAM_IOSCHED_DYNAMIC 1425 isc->trim_stats.queued--; 1426 isc->trim_stats.total++; 1427 isc->trim_stats.pending++; 1428 #endif 1429 return bp; 1430 } 1431 1432 /* 1433 * gets an available trim from the trim queue, if there's no trim 1434 * already pending. It removes this trim from the queue and the device 1435 * must explicitly reinsert it should the need arise. 1436 * 1437 * Assumes we're called with the periph lock held. 1438 */ 1439 struct bio * 1440 cam_iosched_get_trim(struct cam_iosched_softc *isc) 1441 { 1442 #ifdef CAM_IOSCHED_DYNAMIC 1443 struct bio *bp; 1444 #endif 1445 1446 if (!cam_iosched_has_more_trim(isc)) 1447 return NULL; 1448 #ifdef CAM_IOSCHED_DYNAMIC 1449 bp = bioq_first(&isc->trim_queue); 1450 if (bp == NULL) 1451 return NULL; 1452 1453 /* 1454 * If pending read, prefer that based on current read bias setting. The 1455 * read bias is shared for both writes and TRIMs, but on TRIMs the bias 1456 * is for a combined TRIM not a single TRIM request that's come in. 1457 */ 1458 if (do_dynamic_iosched) { 1459 if (bioq_first(&isc->bio_queue) && isc->current_read_bias) { 1460 if (iosched_debug) 1461 printf("Reads present and current_read_bias is %d" 1462 " queued trims %d queued reads %d\n", 1463 isc->current_read_bias, isc->trim_stats.queued, 1464 isc->read_stats.queued); 1465 isc->current_read_bias--; 1466 /* We're not limiting TRIMS, per se, just doing reads first */ 1467 return NULL; 1468 } 1469 /* 1470 * We're going to do a trim, so reset the bias. 1471 */ 1472 isc->current_read_bias = isc->read_bias; 1473 } 1474 1475 /* 1476 * See if our current limiter allows this I/O. Because we only call this 1477 * here, and not in next_trim, the 'bandwidth' limits for trims won't 1478 * work, while the iops or max queued limits will work. It's tricky 1479 * because we want the limits to be from the perspective of the 1480 * "commands sent to the device." To make iops work, we need to check 1481 * only here (since we want all the ops we combine to count as one). To 1482 * make bw limits work, we'd need to check in next_trim, but that would 1483 * have the effect of limiting the iops as seen from the upper layers. 1484 */ 1485 if (cam_iosched_limiter_iop(&isc->trim_stats, bp) != 0) { 1486 if (iosched_debug) 1487 printf("Can't trim because limiter says no.\n"); 1488 isc->trim_stats.state_flags |= IOP_RATE_LIMITED; 1489 return NULL; 1490 } 1491 isc->current_read_bias = isc->read_bias; 1492 isc->trim_stats.state_flags &= ~IOP_RATE_LIMITED; 1493 /* cam_iosched_next_trim below keeps proper book */ 1494 #endif 1495 return cam_iosched_next_trim(isc); 1496 } 1497 1498 /* 1499 * Determine what the next bit of work to do is for the periph. The 1500 * default implementation looks to see if we have trims to do, but no 1501 * trims outstanding. If so, we do that. Otherwise we see if we have 1502 * other work. If we do, then we do that. Otherwise why were we called? 1503 */ 1504 struct bio * 1505 cam_iosched_next_bio(struct cam_iosched_softc *isc) 1506 { 1507 struct bio *bp; 1508 1509 /* 1510 * See if we have a trim that can be scheduled. We can only send one 1511 * at a time down, so this takes that into account. 1512 * 1513 * XXX newer TRIM commands are queueable. Revisit this when we 1514 * implement them. 1515 */ 1516 if ((bp = cam_iosched_get_trim(isc)) != NULL) 1517 return bp; 1518 1519 #ifdef CAM_IOSCHED_DYNAMIC 1520 /* 1521 * See if we have any pending writes, room in the queue for them, 1522 * and no pending reads (unless we've scheduled too many). 1523 * if so, those are next. 1524 */ 1525 if (do_dynamic_iosched) { 1526 if ((bp = cam_iosched_get_write(isc)) != NULL) 1527 return bp; 1528 } 1529 #endif 1530 1531 /* 1532 * next, see if there's other, normal I/O waiting. If so return that. 1533 */ 1534 if ((bp = bioq_first(&isc->bio_queue)) == NULL) 1535 return NULL; 1536 1537 #ifdef CAM_IOSCHED_DYNAMIC 1538 /* 1539 * For the dynamic scheduler, bio_queue is only for reads, so enforce 1540 * the limits here. Enforce only for reads. 1541 */ 1542 if (do_dynamic_iosched) { 1543 if (bp->bio_cmd == BIO_READ && 1544 cam_iosched_limiter_iop(&isc->read_stats, bp) != 0) { 1545 isc->read_stats.state_flags |= IOP_RATE_LIMITED; 1546 return NULL; 1547 } 1548 } 1549 isc->read_stats.state_flags &= ~IOP_RATE_LIMITED; 1550 #endif 1551 bioq_remove(&isc->bio_queue, bp); 1552 #ifdef CAM_IOSCHED_DYNAMIC 1553 if (do_dynamic_iosched) { 1554 if (bp->bio_cmd == BIO_READ) { 1555 isc->read_stats.queued--; 1556 isc->read_stats.total++; 1557 isc->read_stats.pending++; 1558 } else 1559 printf("Found bio_cmd = %#x\n", bp->bio_cmd); 1560 } 1561 if (iosched_debug > 9) 1562 printf("HWQ : %p %#x\n", bp, bp->bio_cmd); 1563 #endif 1564 return bp; 1565 } 1566 1567 /* 1568 * Driver has been given some work to do by the block layer. Tell the 1569 * scheduler about it and have it queue the work up. The scheduler module 1570 * will then return the currently most useful bit of work later, possibly 1571 * deferring work for various reasons. 1572 */ 1573 void 1574 cam_iosched_queue_work(struct cam_iosched_softc *isc, struct bio *bp) 1575 { 1576 1577 /* 1578 * A BIO_SPEEDUP from the uppper layers means that they have a block 1579 * shortage. At the present, this is only sent when we're trying to 1580 * allocate blocks, but have a shortage before giving up. bio_length is 1581 * the size of their shortage. We will complete just enough BIO_DELETEs 1582 * in the queue to satisfy the need. If bio_length is 0, we'll complete 1583 * them all. This allows the scheduler to delay BIO_DELETEs to improve 1584 * read/write performance without worrying about the upper layers. When 1585 * it's possibly a problem, we respond by pretending the BIO_DELETEs 1586 * just worked. We can't do anything about the BIO_DELETEs in the 1587 * hardware, though. We have to wait for them to complete. 1588 */ 1589 if (bp->bio_cmd == BIO_SPEEDUP) { 1590 off_t len; 1591 struct bio *nbp; 1592 1593 len = 0; 1594 while (bioq_first(&isc->trim_queue) && 1595 (bp->bio_length == 0 || len < bp->bio_length)) { 1596 nbp = bioq_takefirst(&isc->trim_queue); 1597 len += nbp->bio_length; 1598 nbp->bio_error = 0; 1599 biodone(nbp); 1600 } 1601 if (bp->bio_length > 0) { 1602 if (bp->bio_length > len) 1603 bp->bio_resid = bp->bio_length - len; 1604 else 1605 bp->bio_resid = 0; 1606 } 1607 bp->bio_error = 0; 1608 biodone(bp); 1609 return; 1610 } 1611 1612 /* 1613 * If we get a BIO_FLUSH, and we're doing delayed BIO_DELETEs then we 1614 * set the last tick time to one less than the current ticks minus the 1615 * delay to force the BIO_DELETEs to be presented to the client driver. 1616 */ 1617 if (bp->bio_cmd == BIO_FLUSH && isc->trim_ticks > 0) 1618 isc->last_trim_tick = ticks - isc->trim_ticks - 1; 1619 1620 /* 1621 * Put all trims on the trim queue. Otherwise put the work on the bio 1622 * queue. 1623 */ 1624 if (bp->bio_cmd == BIO_DELETE) { 1625 bioq_insert_tail(&isc->trim_queue, bp); 1626 if (isc->queued_trims == 0) 1627 isc->last_trim_tick = ticks; 1628 isc->queued_trims++; 1629 #ifdef CAM_IOSCHED_DYNAMIC 1630 isc->trim_stats.in++; 1631 isc->trim_stats.queued++; 1632 #endif 1633 } 1634 #ifdef CAM_IOSCHED_DYNAMIC 1635 else if (do_dynamic_iosched && (bp->bio_cmd != BIO_READ)) { 1636 if (cam_iosched_sort_queue(isc)) 1637 bioq_disksort(&isc->write_queue, bp); 1638 else 1639 bioq_insert_tail(&isc->write_queue, bp); 1640 if (iosched_debug > 9) 1641 printf("Qw : %p %#x\n", bp, bp->bio_cmd); 1642 if (bp->bio_cmd == BIO_WRITE) { 1643 isc->write_stats.in++; 1644 isc->write_stats.queued++; 1645 } 1646 } 1647 #endif 1648 else { 1649 if (cam_iosched_sort_queue(isc)) 1650 bioq_disksort(&isc->bio_queue, bp); 1651 else 1652 bioq_insert_tail(&isc->bio_queue, bp); 1653 #ifdef CAM_IOSCHED_DYNAMIC 1654 if (iosched_debug > 9) 1655 printf("Qr : %p %#x\n", bp, bp->bio_cmd); 1656 if (bp->bio_cmd == BIO_READ) { 1657 isc->read_stats.in++; 1658 isc->read_stats.queued++; 1659 } else if (bp->bio_cmd == BIO_WRITE) { 1660 isc->write_stats.in++; 1661 isc->write_stats.queued++; 1662 } 1663 #endif 1664 } 1665 } 1666 1667 /* 1668 * If we have work, get it scheduled. Called with the periph lock held. 1669 */ 1670 void 1671 cam_iosched_schedule(struct cam_iosched_softc *isc, struct cam_periph *periph) 1672 { 1673 1674 if (cam_iosched_has_work(isc)) 1675 xpt_schedule(periph, CAM_PRIORITY_NORMAL); 1676 } 1677 1678 /* 1679 * Complete a trim request. Mark that we no longer have one in flight. 1680 */ 1681 void 1682 cam_iosched_trim_done(struct cam_iosched_softc *isc) 1683 { 1684 1685 isc->flags &= ~CAM_IOSCHED_FLAG_TRIM_ACTIVE; 1686 } 1687 1688 /* 1689 * Complete a bio. Called before we release the ccb with xpt_release_ccb so we 1690 * might use notes in the ccb for statistics. 1691 */ 1692 int 1693 cam_iosched_bio_complete(struct cam_iosched_softc *isc, struct bio *bp, 1694 union ccb *done_ccb) 1695 { 1696 int retval = 0; 1697 #ifdef CAM_IOSCHED_DYNAMIC 1698 if (!do_dynamic_iosched) 1699 return retval; 1700 1701 if (iosched_debug > 10) 1702 printf("done: %p %#x\n", bp, bp->bio_cmd); 1703 if (bp->bio_cmd == BIO_WRITE) { 1704 retval = cam_iosched_limiter_iodone(&isc->write_stats, bp); 1705 if ((bp->bio_flags & BIO_ERROR) != 0) 1706 isc->write_stats.errs++; 1707 isc->write_stats.out++; 1708 isc->write_stats.pending--; 1709 } else if (bp->bio_cmd == BIO_READ) { 1710 retval = cam_iosched_limiter_iodone(&isc->read_stats, bp); 1711 if ((bp->bio_flags & BIO_ERROR) != 0) 1712 isc->read_stats.errs++; 1713 isc->read_stats.out++; 1714 isc->read_stats.pending--; 1715 } else if (bp->bio_cmd == BIO_DELETE) { 1716 if ((bp->bio_flags & BIO_ERROR) != 0) 1717 isc->trim_stats.errs++; 1718 isc->trim_stats.out++; 1719 isc->trim_stats.pending--; 1720 } else if (bp->bio_cmd != BIO_FLUSH) { 1721 if (iosched_debug) 1722 printf("Completing command with bio_cmd == %#x\n", bp->bio_cmd); 1723 } 1724 1725 if ((bp->bio_flags & BIO_ERROR) == 0 && done_ccb != NULL && 1726 (done_ccb->ccb_h.status & CAM_QOS_VALID) != 0) { 1727 sbintime_t sim_latency; 1728 1729 sim_latency = cam_iosched_sbintime_t(done_ccb->ccb_h.qos.periph_data); 1730 1731 cam_iosched_io_metric_update(isc, sim_latency, 1732 bp->bio_cmd, bp->bio_bcount); 1733 /* 1734 * Debugging code: allow callbacks to the periph driver when latency max 1735 * is exceeded. This can be useful for triggering external debugging actions. 1736 */ 1737 if (isc->latfcn && isc->max_lat != 0 && sim_latency > isc->max_lat) 1738 isc->latfcn(isc->latarg, sim_latency, bp); 1739 } 1740 1741 #endif 1742 return retval; 1743 } 1744 1745 /* 1746 * Tell the io scheduler that you've pushed a trim down into the sim. 1747 * This also tells the I/O scheduler not to push any more trims down, so 1748 * some periphs do not call it if they can cope with multiple trims in flight. 1749 */ 1750 void 1751 cam_iosched_submit_trim(struct cam_iosched_softc *isc) 1752 { 1753 1754 isc->flags |= CAM_IOSCHED_FLAG_TRIM_ACTIVE; 1755 } 1756 1757 /* 1758 * Change the sorting policy hint for I/O transactions for this device. 1759 */ 1760 void 1761 cam_iosched_set_sort_queue(struct cam_iosched_softc *isc, int val) 1762 { 1763 1764 isc->sort_io_queue = val; 1765 } 1766 1767 int 1768 cam_iosched_has_work_flags(struct cam_iosched_softc *isc, uint32_t flags) 1769 { 1770 return isc->flags & flags; 1771 } 1772 1773 void 1774 cam_iosched_set_work_flags(struct cam_iosched_softc *isc, uint32_t flags) 1775 { 1776 isc->flags |= flags; 1777 } 1778 1779 void 1780 cam_iosched_clr_work_flags(struct cam_iosched_softc *isc, uint32_t flags) 1781 { 1782 isc->flags &= ~flags; 1783 } 1784 1785 #ifdef CAM_IOSCHED_DYNAMIC 1786 /* 1787 * After the method presented in Jack Crenshaw's 1998 article "Integer 1788 * Square Roots," reprinted at 1789 * http://www.embedded.com/electronics-blogs/programmer-s-toolbox/4219659/Integer-Square-Roots 1790 * and well worth the read. Briefly, we find the power of 4 that's the 1791 * largest smaller than val. We then check each smaller power of 4 to 1792 * see if val is still bigger. The right shifts at each step divide 1793 * the result by 2 which after successive application winds up 1794 * accumulating the right answer. It could also have been accumulated 1795 * using a separate root counter, but this code is smaller and faster 1796 * than that method. This method is also integer size invariant. 1797 * It returns floor(sqrt((float)val)), or the largest integer less than 1798 * or equal to the square root. 1799 */ 1800 static uint64_t 1801 isqrt64(uint64_t val) 1802 { 1803 uint64_t res = 0; 1804 uint64_t bit = 1ULL << (sizeof(uint64_t) * NBBY - 2); 1805 1806 /* 1807 * Find the largest power of 4 smaller than val. 1808 */ 1809 while (bit > val) 1810 bit >>= 2; 1811 1812 /* 1813 * Accumulate the answer, one bit at a time (we keep moving 1814 * them over since 2 is the square root of 4 and we test 1815 * powers of 4). We accumulate where we find the bit, but 1816 * the successive shifts land the bit in the right place 1817 * by the end. 1818 */ 1819 while (bit != 0) { 1820 if (val >= res + bit) { 1821 val -= res + bit; 1822 res = (res >> 1) + bit; 1823 } else 1824 res >>= 1; 1825 bit >>= 2; 1826 } 1827 1828 return res; 1829 } 1830 1831 static sbintime_t latencies[LAT_BUCKETS - 1] = { 1832 BUCKET_BASE << 0, /* 20us */ 1833 BUCKET_BASE << 1, 1834 BUCKET_BASE << 2, 1835 BUCKET_BASE << 3, 1836 BUCKET_BASE << 4, 1837 BUCKET_BASE << 5, 1838 BUCKET_BASE << 6, 1839 BUCKET_BASE << 7, 1840 BUCKET_BASE << 8, 1841 BUCKET_BASE << 9, 1842 BUCKET_BASE << 10, 1843 BUCKET_BASE << 11, 1844 BUCKET_BASE << 12, 1845 BUCKET_BASE << 13, 1846 BUCKET_BASE << 14, 1847 BUCKET_BASE << 15, 1848 BUCKET_BASE << 16, 1849 BUCKET_BASE << 17, 1850 BUCKET_BASE << 18 /* 5,242,880us */ 1851 }; 1852 1853 static void 1854 cam_iosched_update(struct iop_stats *iop, sbintime_t sim_latency) 1855 { 1856 sbintime_t y, deltasq, delta; 1857 int i; 1858 1859 /* 1860 * Keep counts for latency. We do it by power of two buckets. 1861 * This helps us spot outlier behavior obscured by averages. 1862 */ 1863 for (i = 0; i < LAT_BUCKETS - 1; i++) { 1864 if (sim_latency < latencies[i]) { 1865 iop->latencies[i]++; 1866 break; 1867 } 1868 } 1869 if (i == LAT_BUCKETS - 1) 1870 iop->latencies[i]++; /* Put all > 8192ms values into the last bucket. */ 1871 1872 /* 1873 * Classic exponentially decaying average with a tiny alpha 1874 * (2 ^ -alpha_bits). For more info see the NIST statistical 1875 * handbook. 1876 * 1877 * ema_t = y_t * alpha + ema_t-1 * (1 - alpha) [nist] 1878 * ema_t = y_t * alpha + ema_t-1 - alpha * ema_t-1 1879 * ema_t = alpha * y_t - alpha * ema_t-1 + ema_t-1 1880 * alpha = 1 / (1 << alpha_bits) 1881 * sub e == ema_t-1, b == 1/alpha (== 1 << alpha_bits), d == y_t - ema_t-1 1882 * = y_t/b - e/b + be/b 1883 * = (y_t - e + be) / b 1884 * = (e + d) / b 1885 * 1886 * Since alpha is a power of two, we can compute this w/o any mult or 1887 * division. 1888 * 1889 * Variance can also be computed. Usually, it would be expressed as follows: 1890 * diff_t = y_t - ema_t-1 1891 * emvar_t = (1 - alpha) * (emavar_t-1 + diff_t^2 * alpha) 1892 * = emavar_t-1 - alpha * emavar_t-1 + delta_t^2 * alpha - (delta_t * alpha)^2 1893 * sub b == 1/alpha (== 1 << alpha_bits), e == emavar_t-1, d = delta_t^2 1894 * = e - e/b + dd/b + dd/bb 1895 * = (bbe - be + bdd + dd) / bb 1896 * = (bbe + b(dd-e) + dd) / bb (which is expanded below bb = 1<<(2*alpha_bits)) 1897 */ 1898 /* 1899 * XXX possible numeric issues 1900 * o We assume right shifted integers do the right thing, since that's 1901 * implementation defined. You can change the right shifts to / (1LL << alpha). 1902 * o alpha_bits = 9 gives ema ceiling of 23 bits of seconds for ema and 14 bits 1903 * for emvar. This puts a ceiling of 13 bits on alpha since we need a 1904 * few tens of seconds of representation. 1905 * o We mitigate alpha issues by never setting it too high. 1906 */ 1907 y = sim_latency; 1908 delta = (y - iop->ema); /* d */ 1909 iop->ema = ((iop->ema << alpha_bits) + delta) >> alpha_bits; 1910 1911 /* 1912 * Were we to naively plow ahead at this point, we wind up with many numerical 1913 * issues making any SD > ~3ms unreliable. So, we shift right by 12. This leaves 1914 * us with microsecond level precision in the input, so the same in the 1915 * output. It means we can't overflow deltasq unless delta > 4k seconds. It 1916 * also means that emvar can be up 46 bits 40 of which are fraction, which 1917 * gives us a way to measure up to ~8s in the SD before the computation goes 1918 * unstable. Even the worst hard disk rarely has > 1s service time in the 1919 * drive. It does mean we have to shift left 12 bits after taking the 1920 * square root to compute the actual standard deviation estimate. This loss of 1921 * precision is preferable to needing int128 types to work. The above numbers 1922 * assume alpha=9. 10 or 11 are ok, but we start to run into issues at 12, 1923 * so 12 or 13 is OK for EMA, EMVAR and SD will be wrong in those cases. 1924 */ 1925 delta >>= 12; 1926 deltasq = delta * delta; /* dd */ 1927 iop->emvar = ((iop->emvar << (2 * alpha_bits)) + /* bbe */ 1928 ((deltasq - iop->emvar) << alpha_bits) + /* b(dd-e) */ 1929 deltasq) /* dd */ 1930 >> (2 * alpha_bits); /* div bb */ 1931 iop->sd = (sbintime_t)isqrt64((uint64_t)iop->emvar) << 12; 1932 } 1933 1934 static void 1935 cam_iosched_io_metric_update(struct cam_iosched_softc *isc, 1936 sbintime_t sim_latency, int cmd, size_t size) 1937 { 1938 /* xxx Do we need to scale based on the size of the I/O ? */ 1939 switch (cmd) { 1940 case BIO_READ: 1941 cam_iosched_update(&isc->read_stats, sim_latency); 1942 break; 1943 case BIO_WRITE: 1944 cam_iosched_update(&isc->write_stats, sim_latency); 1945 break; 1946 case BIO_DELETE: 1947 cam_iosched_update(&isc->trim_stats, sim_latency); 1948 break; 1949 default: 1950 break; 1951 } 1952 } 1953 1954 #ifdef DDB 1955 static int biolen(struct bio_queue_head *bq) 1956 { 1957 int i = 0; 1958 struct bio *bp; 1959 1960 TAILQ_FOREACH(bp, &bq->queue, bio_queue) { 1961 i++; 1962 } 1963 return i; 1964 } 1965 1966 /* 1967 * Show the internal state of the I/O scheduler. 1968 */ 1969 DB_SHOW_COMMAND(iosched, cam_iosched_db_show) 1970 { 1971 struct cam_iosched_softc *isc; 1972 1973 if (!have_addr) { 1974 db_printf("Need addr\n"); 1975 return; 1976 } 1977 isc = (struct cam_iosched_softc *)addr; 1978 db_printf("pending_reads: %d\n", isc->read_stats.pending); 1979 db_printf("min_reads: %d\n", isc->read_stats.min); 1980 db_printf("max_reads: %d\n", isc->read_stats.max); 1981 db_printf("reads: %d\n", isc->read_stats.total); 1982 db_printf("in_reads: %d\n", isc->read_stats.in); 1983 db_printf("out_reads: %d\n", isc->read_stats.out); 1984 db_printf("queued_reads: %d\n", isc->read_stats.queued); 1985 db_printf("Read Q len %d\n", biolen(&isc->bio_queue)); 1986 db_printf("pending_writes: %d\n", isc->write_stats.pending); 1987 db_printf("min_writes: %d\n", isc->write_stats.min); 1988 db_printf("max_writes: %d\n", isc->write_stats.max); 1989 db_printf("writes: %d\n", isc->write_stats.total); 1990 db_printf("in_writes: %d\n", isc->write_stats.in); 1991 db_printf("out_writes: %d\n", isc->write_stats.out); 1992 db_printf("queued_writes: %d\n", isc->write_stats.queued); 1993 db_printf("Write Q len %d\n", biolen(&isc->write_queue)); 1994 db_printf("pending_trims: %d\n", isc->trim_stats.pending); 1995 db_printf("min_trims: %d\n", isc->trim_stats.min); 1996 db_printf("max_trims: %d\n", isc->trim_stats.max); 1997 db_printf("trims: %d\n", isc->trim_stats.total); 1998 db_printf("in_trims: %d\n", isc->trim_stats.in); 1999 db_printf("out_trims: %d\n", isc->trim_stats.out); 2000 db_printf("queued_trims: %d\n", isc->trim_stats.queued); 2001 db_printf("Trim Q len %d\n", biolen(&isc->trim_queue)); 2002 db_printf("read_bias: %d\n", isc->read_bias); 2003 db_printf("current_read_bias: %d\n", isc->current_read_bias); 2004 db_printf("Trim active? %s\n", 2005 (isc->flags & CAM_IOSCHED_FLAG_TRIM_ACTIVE) ? "yes" : "no"); 2006 } 2007 #endif 2008 #endif 2009