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
  17typedef struct {
  18    int64_t slice_start_time;
  19    int64_t slice_end_time;
  20    uint64_t slice_quota;
  21    uint64_t slice_ns;
  22    uint64_t dispatched;
  23} RateLimit;
  24
  25/** Calculate and return delay for next request in ns
  26 *
  27 * Record that we sent @n data units (where @n matches the scale chosen
  28 * during ratelimit_set_speed). If we may send more data units
  29 * in the current time slice, return 0 (i.e. no delay). Otherwise
  30 * return the amount of time (in ns) until the start of the next time
  31 * slice that will permit sending the next chunk of data.
  32 *
  33 * Recording sent data units even after exceeding the quota is
  34 * permitted; the time slice will be extended accordingly.
  35 */
  36static inline int64_t ratelimit_calculate_delay(RateLimit *limit, uint64_t n)
  37{
  38    int64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
  39    double delay_slices;
  40
  41    assert(limit->slice_quota && limit->slice_ns);
  42
  43    if (limit->slice_end_time < now) {
  44        /* Previous, possibly extended, time slice finished; reset the
  45         * accounting. */
  46        limit->slice_start_time = now;
  47        limit->slice_end_time = now + limit->slice_ns;
  48        limit->dispatched = 0;
  49    }
  50
  51    limit->dispatched += n;
  52    if (limit->dispatched < limit->slice_quota) {
  53        /* We may send further data within the current time slice, no
  54         * need to delay the next request. */
  55        return 0;
  56    }
  57
  58    /* Quota exceeded. Wait based on the excess amount and then start a new
  59     * slice. */
  60    delay_slices = (double)limit->dispatched / limit->slice_quota;
  61    limit->slice_end_time = limit->slice_start_time +
  62        (uint64_t)(delay_slices * limit->slice_ns);
  63    return limit->slice_end_time - now;
  64}
  65
  66static inline void ratelimit_set_speed(RateLimit *limit, uint64_t speed,
  67                                       uint64_t slice_ns)
  68{
  69    limit->slice_ns = slice_ns;
  70    limit->slice_quota = MAX(((double)speed * slice_ns) / 1000000000ULL, 1);
  71}
  72
  73#endif
  74