1 /* 2 * Ratelimiting calculations 3 * 4 * Copyright IBM, Corp. 2011 5 * 6 * Authors: 7 * Stefan Hajnoczi <stefanha@linux.vnet.ibm.com> 8 * 9 * This work is licensed under the terms of the GNU LGPL, version 2 or later. 10 * See the COPYING.LIB file in the top-level directory. 11 * 12 */ 13 14 #ifndef QEMU_RATELIMIT_H 15 #define QEMU_RATELIMIT_H 16 17 #include "qemu/timer.h" 18 19 typedef struct { 20 int64_t slice_start_time; 21 int64_t slice_end_time; 22 uint64_t slice_quota; 23 uint64_t slice_ns; 24 uint64_t dispatched; 25 } RateLimit; 26 27 /** Calculate and return delay for next request in ns 28 * 29 * Record that we sent @n data units (where @n matches the scale chosen 30 * during ratelimit_set_speed). If we may send more data units 31 * in the current time slice, return 0 (i.e. no delay). Otherwise 32 * return the amount of time (in ns) until the start of the next time 33 * slice that will permit sending the next chunk of data. 34 * 35 * Recording sent data units even after exceeding the quota is 36 * permitted; the time slice will be extended accordingly. 37 */ 38 static inline int64_t ratelimit_calculate_delay(RateLimit *limit, uint64_t n) 39 { 40 int64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME); 41 double delay_slices; 42 43 assert(limit->slice_quota && limit->slice_ns); 44 45 if (limit->slice_end_time < now) { 46 /* Previous, possibly extended, time slice finished; reset the 47 * accounting. */ 48 limit->slice_start_time = now; 49 limit->slice_end_time = now + limit->slice_ns; 50 limit->dispatched = 0; 51 } 52 53 limit->dispatched += n; 54 if (limit->dispatched < limit->slice_quota) { 55 /* We may send further data within the current time slice, no 56 * need to delay the next request. */ 57 return 0; 58 } 59 60 /* Quota exceeded. Wait based on the excess amount and then start a new 61 * slice. */ 62 delay_slices = (double)limit->dispatched / limit->slice_quota; 63 limit->slice_end_time = limit->slice_start_time + 64 (uint64_t)(delay_slices * limit->slice_ns); 65 return limit->slice_end_time - now; 66 } 67 68 static inline void ratelimit_set_speed(RateLimit *limit, uint64_t speed, 69 uint64_t slice_ns) 70 { 71 limit->slice_ns = slice_ns; 72 limit->slice_quota = MAX(((double)speed * slice_ns) / 1000000000ULL, 1); 73 } 74 75 #endif 76