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720507ed95
Both users of RateLimit, block-copy.c and blockjob.c, treat a speed of zero as unlimited, while RateLimit treats it as "as slow as possible". The latter is nicer from the code point of view but pretty useless, so disable rate limiting if a speed of zero is provided. Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com> Message-Id: <20210614081130.22134-2-eesposit@redhat.com> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
98 lines
2.7 KiB
C
98 lines
2.7 KiB
C
/*
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* Ratelimiting calculations
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*
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* Copyright IBM, Corp. 2011
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*
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* Authors:
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* Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
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*
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* This work is licensed under the terms of the GNU LGPL, version 2 or later.
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* See the COPYING.LIB file in the top-level directory.
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*
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*/
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#ifndef QEMU_RATELIMIT_H
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#define QEMU_RATELIMIT_H
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#include "qemu/lockable.h"
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#include "qemu/timer.h"
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typedef struct {
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QemuMutex lock;
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int64_t slice_start_time;
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int64_t slice_end_time;
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uint64_t slice_quota;
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uint64_t slice_ns;
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uint64_t dispatched;
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} RateLimit;
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/** Calculate and return delay for next request in ns
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*
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* Record that we sent @n data units (where @n matches the scale chosen
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* during ratelimit_set_speed). If we may send more data units
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* in the current time slice, return 0 (i.e. no delay). Otherwise
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* return the amount of time (in ns) until the start of the next time
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* slice that will permit sending the next chunk of data.
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*
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* Recording sent data units even after exceeding the quota is
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* permitted; the time slice will be extended accordingly.
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*/
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static inline int64_t ratelimit_calculate_delay(RateLimit *limit, uint64_t n)
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{
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int64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
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double delay_slices;
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QEMU_LOCK_GUARD(&limit->lock);
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if (!limit->slice_quota) {
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/* Throttling disabled. */
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return 0;
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}
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assert(limit->slice_ns);
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if (limit->slice_end_time < now) {
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/* Previous, possibly extended, time slice finished; reset the
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* accounting. */
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limit->slice_start_time = now;
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limit->slice_end_time = now + limit->slice_ns;
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limit->dispatched = 0;
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}
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limit->dispatched += n;
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if (limit->dispatched < limit->slice_quota) {
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/* We may send further data within the current time slice, no
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* need to delay the next request. */
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return 0;
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}
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/* Quota exceeded. Wait based on the excess amount and then start a new
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* slice. */
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delay_slices = (double)limit->dispatched / limit->slice_quota;
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limit->slice_end_time = limit->slice_start_time +
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(uint64_t)(delay_slices * limit->slice_ns);
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return limit->slice_end_time - now;
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}
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static inline void ratelimit_init(RateLimit *limit)
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{
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qemu_mutex_init(&limit->lock);
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}
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static inline void ratelimit_destroy(RateLimit *limit)
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{
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qemu_mutex_destroy(&limit->lock);
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}
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static inline void ratelimit_set_speed(RateLimit *limit, uint64_t speed,
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uint64_t slice_ns)
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{
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QEMU_LOCK_GUARD(&limit->lock);
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limit->slice_ns = slice_ns;
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if (speed == 0) {
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limit->slice_quota = 0;
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} else {
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limit->slice_quota = MAX(((double)speed * slice_ns) / 1000000000ULL, 1);
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}
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}
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#endif
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