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/*
* Ratelimiting calculations
*
* Copyright IBM, Corp. 2011
*
* Authors:
* Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
*
* This work is licensed under the terms of the GNU LGPL, version 2 or later.
* See the COPYING.LIB file in the top-level directory.
*
*/
#ifndef QEMU_RATELIMIT_H
#define QEMU_RATELIMIT_H
#include "qemu/timer.h"
typedef struct {
int64_t slice_start_time;
int64_t slice_end_time;
uint64_t slice_quota;
uint64_t slice_ns;
uint64_t dispatched;
} RateLimit;
/** Calculate and return delay for next request in ns
*
* Record that we sent @n data units (where @n matches the scale chosen
* during ratelimit_set_speed). If we may send more data units
* in the current time slice, return 0 (i.e. no delay). Otherwise
* return the amount of time (in ns) until the start of the next time
* slice that will permit sending the next chunk of data.
*
* Recording sent data units even after exceeding the quota is
* permitted; the time slice will be extended accordingly.
*/
static inline int64_t ratelimit_calculate_delay(RateLimit *limit, uint64_t n)
{
int64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
double delay_slices;
assert(limit->slice_quota && limit->slice_ns);
if (limit->slice_end_time < now) {
/* Previous, possibly extended, time slice finished; reset the
* accounting. */
limit->slice_start_time = now;
limit->slice_end_time = now + limit->slice_ns;
limit->dispatched = 0;
}
limit->dispatched += n;
if (limit->dispatched < limit->slice_quota) {
/* We may send further data within the current time slice, no
* need to delay the next request. */
return 0;
}
/* Quota exceeded. Wait based on the excess amount and then start a new
* slice. */
delay_slices = (double)limit->dispatched / limit->slice_quota;
limit->slice_end_time = limit->slice_start_time +
(uint64_t)(delay_slices * limit->slice_ns);
return limit->slice_end_time - now;
}
static inline void ratelimit_set_speed(RateLimit *limit, uint64_t speed,
uint64_t slice_ns)
{
limit->slice_ns = slice_ns;
limit->slice_quota = MAX(((double)speed * slice_ns) / 1000000000ULL, 1);
}
#endif
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