1 /* 2 * Copyright (c) 2005 Jeffrey M. Hsu. All rights reserved. 3 * 4 * This code is derived from software contributed to The DragonFly Project 5 * by Jeffrey M. Hsu. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. Neither the name of The DragonFly Project nor the names of its 16 * contributors may be used to endorse or promote products derived 17 * from this software without specific, prior written permission. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 21 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 22 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 23 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 24 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING, 25 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 26 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 27 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 28 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 29 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30 * SUCH DAMAGE. 31 * 32 * $DragonFly: src/sys/kern/kern_spinlock.c,v 1.2 2005/09/16 21:50:12 dillon Exp $ 33 */ 34 35 #include <sys/param.h> 36 #include <sys/types.h> 37 #include <machine/atomic.h> 38 #include <sys/spinlock.h> 39 #include <sys/spinlock2.h> 40 41 #define BACKOFF_INITIAL 1 42 #define BACKOFF_LIMIT 256 43 44 #ifdef SMP 45 46 void 47 spin_lock_contested(struct spinlock *mtx) 48 { 49 int i, backoff = BACKOFF_INITIAL; 50 51 do { 52 /* exponential backoff to reduce contention */ 53 for (i = 0; i < backoff; i++) 54 cpu_nop(); 55 if (backoff < BACKOFF_LIMIT) 56 backoff <<= 1; 57 /* do non-bus-locked check first */ 58 } while (mtx->lock != 0 || atomic_swap_int(&mtx->lock, 1) != 0); 59 } 60 61 #endif 62