LXR qemu/include/qemu/ratelimit.h

   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/lockable.h"
  18#include "qemu/timer.h"
  19
  20typedef struct {
  21    QemuMutex lock;
  22    int64_t slice_start_time;
  23    int64_t slice_end_time;
  24    uint64_t slice_quota;
  25    uint64_t slice_ns;
  26    uint64_t dispatched;
  27} RateLimit;
  28
  29/** Calculate and return delay for next request in ns
  30 *
  31 * Record that we sent @n data units (where @n matches the scale chosen
  32 * during ratelimit_set_speed). If we may send more data units
  33 * in the current time slice, return 0 (i.e. no delay). Otherwise
  34 * return the amount of time (in ns) until the start of the next time
  35 * slice that will permit sending the next chunk of data.
  36 *
  37 * Recording sent data units even after exceeding the quota is
  38 * permitted; the time slice will be extended accordingly.
  39 */
  40static inline int64_t ratelimit_calculate_delay(RateLimit *limit, uint64_t n)
  41{
  42    int64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
  43    double delay_slices;
  44
  45    QEMU_LOCK_GUARD(&limit->lock);
  46    if (!limit->slice_quota) {
  47        /* Throttling disabled.  */
  48        return 0;
  49    }
  50    assert(limit->slice_ns);
  51
  52    if (limit->slice_end_time < now) {
  53        /* Previous, possibly extended, time slice finished; reset the
  54         * accounting. */
  55        limit->slice_start_time = now;
  56        limit->slice_end_time = now + limit->slice_ns;
  57        limit->dispatched = 0;
  58    }
  59
  60    limit->dispatched += n;
  61    if (limit->dispatched < limit->slice_quota) {
  62        /* We may send further data within the current time slice, no
  63         * need to delay the next request. */
  64        return 0;
  65    }
  66
  67    /* Quota exceeded. Wait based on the excess amount and then start a new
  68     * slice. */
  69    delay_slices = (double)limit->dispatched / limit->slice_quota;
  70    limit->slice_end_time = limit->slice_start_time +
  71        (uint64_t)(delay_slices * limit->slice_ns);
  72    return limit->slice_end_time - now;
  73}
  74
  75static inline void ratelimit_init(RateLimit *limit)
  76{
  77    qemu_mutex_init(&limit->lock);
  78}
  79
  80static inline void ratelimit_destroy(RateLimit *limit)
  81{
  82    qemu_mutex_destroy(&limit->lock);
  83}
  84
  85static inline void ratelimit_set_speed(RateLimit *limit, uint64_t speed,
  86                                       uint64_t slice_ns)
  87{
  88    QEMU_LOCK_GUARD(&limit->lock);
  89    limit->slice_ns = slice_ns;
  90    if (speed == 0) {
  91        limit->slice_quota = 0;
  92    } else {
  93        limit->slice_quota = MAX(((double)speed * slice_ns) / 1000000000ULL, 1);
  94    }
  95}
  96
  97#endif
  98