[mirror_qemu.git] / util / throttle.c

/*
 * QEMU throttling infrastructure
 *
 * Copyright (C) Nodalink, EURL. 2013-2014
 * Copyright (C) Igalia, S.L. 2015
 *
 * Authors:
 *   Benoît Canet <benoit.canet@nodalink.com>
 *   Alberto Garcia <berto@igalia.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 or
 * (at your option) version 3 of the License.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 */

#include "qemu/throttle.h"
#include "qemu/timer.h"
#include "block/aio.h"

/* This function make a bucket leak
 *
 * @bkt:   the bucket to make leak
 * @delta_ns: the time delta
 */
void throttle_leak_bucket(LeakyBucket *bkt, int64_t delta_ns)
{
    double leak;

    /* compute how much to leak */
    leak = (bkt->avg * (double) delta_ns) / NANOSECONDS_PER_SECOND;

    /* make the bucket leak */
    bkt->level = MAX(bkt->level - leak, 0);
}

/* Calculate the time delta since last leak and make proportionals leaks
 *
 * @now:      the current timestamp in ns
 */
static void throttle_do_leak(ThrottleState *ts, int64_t now)
{
    /* compute the time elapsed since the last leak */
    int64_t delta_ns = now - ts->previous_leak;
    int i;

    ts->previous_leak = now;

    if (delta_ns <= 0) {
        return;
    }

    /* make each bucket leak */
    for (i = 0; i < BUCKETS_COUNT; i++) {
        throttle_leak_bucket(&ts->cfg.buckets[i], delta_ns);
    }
}

/* do the real job of computing the time to wait
 *
 * @limit: the throttling limit
 * @extra: the number of operation to delay
 * @ret:   the time to wait in ns
 */
static int64_t throttle_do_compute_wait(double limit, double extra)
{
    double wait = extra * NANOSECONDS_PER_SECOND;
    wait /= limit;
    return wait;
}

/* This function compute the wait time in ns that a leaky bucket should trigger
 *
 * @bkt: the leaky bucket we operate on
 * @ret: the resulting wait time in ns or 0 if the operation can go through
 */
int64_t throttle_compute_wait(LeakyBucket *bkt)
{
    double extra; /* the number of extra units blocking the io */

    if (!bkt->avg) {
        return 0;
    }

    extra = bkt->level - bkt->max;

    if (extra <= 0) {
        return 0;
    }

    return throttle_do_compute_wait(bkt->avg, extra);
}

/* This function compute the time that must be waited while this IO
 *
 * @is_write:   true if the current IO is a write, false if it's a read
 * @ret:        time to wait
 */
static int64_t throttle_compute_wait_for(ThrottleState *ts,
                                         bool is_write)
{
    BucketType to_check[2][4] = { {THROTTLE_BPS_TOTAL,
                                   THROTTLE_OPS_TOTAL,
                                   THROTTLE_BPS_READ,
                                   THROTTLE_OPS_READ},
                                  {THROTTLE_BPS_TOTAL,
                                   THROTTLE_OPS_TOTAL,
                                   THROTTLE_BPS_WRITE,
                                   THROTTLE_OPS_WRITE}, };
    int64_t wait, max_wait = 0;
    int i;

    for (i = 0; i < 4; i++) {
        BucketType index = to_check[is_write][i];
        wait = throttle_compute_wait(&ts->cfg.buckets[index]);
        if (wait > max_wait) {
            max_wait = wait;
        }
    }

    return max_wait;
}

/* compute the timer for this type of operation
 *
 * @is_write:   the type of operation
 * @now:        the current clock timestamp
 * @next_timestamp: the resulting timer
 * @ret:        true if a timer must be set
 */
bool throttle_compute_timer(ThrottleState *ts,
                            bool is_write,
                            int64_t now,
                            int64_t *next_timestamp)
{
    int64_t wait;

    /* leak proportionally to the time elapsed */
    throttle_do_leak(ts, now);

    /* compute the wait time if any */
    wait = throttle_compute_wait_for(ts, is_write);

    /* if the code must wait compute when the next timer should fire */
    if (wait) {
        *next_timestamp = now + wait;
        return true;
    }

    /* else no need to wait at all */
    *next_timestamp = now;
    return false;
}

/* Add timers to event loop */
void throttle_timers_attach_aio_context(ThrottleTimers *tt,
                                        AioContext *new_context)
{
    tt->timers[0] = aio_timer_new(new_context, tt->clock_type, SCALE_NS,
                                  tt->read_timer_cb, tt->timer_opaque);
    tt->timers[1] = aio_timer_new(new_context, tt->clock_type, SCALE_NS,
                                  tt->write_timer_cb, tt->timer_opaque);
}

/* To be called first on the ThrottleState */
void throttle_init(ThrottleState *ts)
{
    memset(ts, 0, sizeof(ThrottleState));
}

/* To be called first on the ThrottleTimers */
void throttle_timers_init(ThrottleTimers *tt,
                          AioContext *aio_context,
                          QEMUClockType clock_type,
                          QEMUTimerCB *read_timer_cb,
                          QEMUTimerCB *write_timer_cb,
                          void *timer_opaque)
{
    memset(tt, 0, sizeof(ThrottleTimers));

    tt->clock_type = clock_type;
    tt->read_timer_cb = read_timer_cb;
    tt->write_timer_cb = write_timer_cb;
    tt->timer_opaque = timer_opaque;
    throttle_timers_attach_aio_context(tt, aio_context);
}

/* destroy a timer */
static void throttle_timer_destroy(QEMUTimer **timer)
{
    assert(*timer != NULL);

    timer_del(*timer);
    timer_free(*timer);
    *timer = NULL;
}

/* Remove timers from event loop */
void throttle_timers_detach_aio_context(ThrottleTimers *tt)
{
    int i;

    for (i = 0; i < 2; i++) {
        throttle_timer_destroy(&tt->timers[i]);
    }
}

/* To be called last on the ThrottleTimers */
void throttle_timers_destroy(ThrottleTimers *tt)
{
    throttle_timers_detach_aio_context(tt);
}

/* is any throttling timer configured */
bool throttle_timers_are_initialized(ThrottleTimers *tt)
{
    if (tt->timers[0]) {
        return true;
    }

    return false;
}

/* Does any throttling must be done
 *
 * @cfg: the throttling configuration to inspect
 * @ret: true if throttling must be done else false
 */
bool throttle_enabled(ThrottleConfig *cfg)
{
    int i;

    for (i = 0; i < BUCKETS_COUNT; i++) {
        if (cfg->buckets[i].avg > 0) {
            return true;
        }
    }

    return false;
}

/* return true if any two throttling parameters conflicts
 *
 * @cfg: the throttling configuration to inspect
 * @ret: true if any conflict detected else false
 */
bool throttle_conflicting(ThrottleConfig *cfg)
{
    bool bps_flag, ops_flag;
    bool bps_max_flag, ops_max_flag;

    bps_flag = cfg->buckets[THROTTLE_BPS_TOTAL].avg &&
               (cfg->buckets[THROTTLE_BPS_READ].avg ||
                cfg->buckets[THROTTLE_BPS_WRITE].avg);

    ops_flag = cfg->buckets[THROTTLE_OPS_TOTAL].avg &&
               (cfg->buckets[THROTTLE_OPS_READ].avg ||
                cfg->buckets[THROTTLE_OPS_WRITE].avg);

    bps_max_flag = cfg->buckets[THROTTLE_BPS_TOTAL].max &&
                  (cfg->buckets[THROTTLE_BPS_READ].max  ||
                   cfg->buckets[THROTTLE_BPS_WRITE].max);

    ops_max_flag = cfg->buckets[THROTTLE_OPS_TOTAL].max &&
                   (cfg->buckets[THROTTLE_OPS_READ].max ||
                   cfg->buckets[THROTTLE_OPS_WRITE].max);

    return bps_flag || ops_flag || bps_max_flag || ops_max_flag;
}

/* check if a throttling configuration is valid
 * @cfg: the throttling configuration to inspect
 * @ret: true if valid else false
 */
bool throttle_is_valid(ThrottleConfig *cfg)
{
    bool invalid = false;
    int i;

    for (i = 0; i < BUCKETS_COUNT; i++) {
        if (cfg->buckets[i].avg < 0) {
            invalid = true;
        }
    }

    for (i = 0; i < BUCKETS_COUNT; i++) {
        if (cfg->buckets[i].max < 0) {
            invalid = true;
        }
    }

    return !invalid;
}

/* check if bps_max/iops_max is used without bps/iops
 * @cfg: the throttling configuration to inspect
 */
bool throttle_max_is_missing_limit(ThrottleConfig *cfg)
{
    int i;

    for (i = 0; i < BUCKETS_COUNT; i++) {
        if (cfg->buckets[i].max && !cfg->buckets[i].avg) {
            return true;
        }
    }
    return false;
}

/* fix bucket parameters */
static void throttle_fix_bucket(LeakyBucket *bkt)
{
    double min;

    /* zero bucket level */
    bkt->level = 0;

    /* The following is done to cope with the Linux CFQ block scheduler
     * which regroup reads and writes by block of 100ms in the guest.
     * When they are two process one making reads and one making writes cfq
     * make a pattern looking like the following:
     * WWWWWWWWWWWRRRRRRRRRRRRRRWWWWWWWWWWWWWwRRRRRRRRRRRRRRRRR
     * Having a max burst value of 100ms of the average will help smooth the
     * throttling
     */
    min = bkt->avg / 10;
    if (bkt->avg && !bkt->max) {
        bkt->max = min;
    }
}

/* take care of canceling a timer */
static void throttle_cancel_timer(QEMUTimer *timer)
{
    assert(timer != NULL);

    timer_del(timer);
}

/* Used to configure the throttle
 *
 * @ts: the throttle state we are working on
 * @tt: the throttle timers we use in this aio context
 * @cfg: the config to set
 */
void throttle_config(ThrottleState *ts,
                     ThrottleTimers *tt,
                     ThrottleConfig *cfg)
{
    int i;

    ts->cfg = *cfg;

    for (i = 0; i < BUCKETS_COUNT; i++) {
        throttle_fix_bucket(&ts->cfg.buckets[i]);
    }

    ts->previous_leak = qemu_clock_get_ns(tt->clock_type);

    for (i = 0; i < 2; i++) {
        throttle_cancel_timer(tt->timers[i]);
    }
}

/* used to get config
 *
 * @ts:  the throttle state we are working on
 * @cfg: the config to write
 */
void throttle_get_config(ThrottleState *ts, ThrottleConfig *cfg)
{
    *cfg = ts->cfg;
}


/* Schedule the read or write timer if needed
 *
 * NOTE: this function is not unit tested due to it's usage of timer_mod
 *
 * @tt:       the timers structure
 * @is_write: the type of operation (read/write)
 * @ret:      true if the timer has been scheduled else false
 */
bool throttle_schedule_timer(ThrottleState *ts,
                             ThrottleTimers *tt,
                             bool is_write)
{
    int64_t now = qemu_clock_get_ns(tt->clock_type);
    int64_t next_timestamp;
    bool must_wait;

    must_wait = throttle_compute_timer(ts,
                                       is_write,
                                       now,
                                       &next_timestamp);

    /* request not throttled */
    if (!must_wait) {
        return false;
    }

    /* request throttled and timer pending -> do nothing */
    if (timer_pending(tt->timers[is_write])) {
        return true;
    }

    /* request throttled and timer not pending -> arm timer */
    timer_mod(tt->timers[is_write], next_timestamp);
    return true;
}

/* do the accounting for this operation
 *
 * @is_write: the type of operation (read/write)
 * @size:     the size of the operation
 */
void throttle_account(ThrottleState *ts, bool is_write, uint64_t size)
{
    double units = 1.0;

    /* if cfg.op_size is defined and smaller than size we compute unit count */
    if (ts->cfg.op_size && size > ts->cfg.op_size) {
        units = (double) size / ts->cfg.op_size;
    }

    ts->cfg.buckets[THROTTLE_BPS_TOTAL].level += size;
    ts->cfg.buckets[THROTTLE_OPS_TOTAL].level += units;

    if (is_write) {
        ts->cfg.buckets[THROTTLE_BPS_WRITE].level += size;
        ts->cfg.buckets[THROTTLE_OPS_WRITE].level += units;
    } else {
        ts->cfg.buckets[THROTTLE_BPS_READ].level += size;
        ts->cfg.buckets[THROTTLE_OPS_READ].level += units;
    }
}
Commit	Line	Data
5ddfffbd BC	1	/*
	2	* QEMU throttling infrastructure
	3	*
a291d5d9 AG	4	* Copyright (C) Nodalink, EURL. 2013-2014
a291d5d9 AG	5	* Copyright (C) Igalia, S.L. 2015
5ddfffbd	6	*
a291d5d9 AG	7	* Authors:
	8	* Benoît Canet <benoit.canet@nodalink.com>
	9	* Alberto Garcia <berto@igalia.com>
5ddfffbd BC	10	*
	11	* This program is free software; you can redistribute it and/or
	12	* modify it under the terms of the GNU General Public License as
	13	* published by the Free Software Foundation; either version 2 or
	14	* (at your option) version 3 of the License.
	15	*
	16	* This program is distributed in the hope that it will be useful,
	17	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	18	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	19	* GNU General Public License for more details.
	20	*
	21	* You should have received a copy of the GNU General Public License
	22	* along with this program; if not, see <http://www.gnu.org/licenses/>.
	23	*/
	24
	25	#include "qemu/throttle.h"
	26	#include "qemu/timer.h"
13af91eb	27	#include "block/aio.h"
5ddfffbd BC	28
	29	/* This function make a bucket leak
	30	*
	31	* @bkt: the bucket to make leak
	32	* @delta_ns: the time delta
	33	*/
	34	void throttle_leak_bucket(LeakyBucket *bkt, int64_t delta_ns)
	35	{
	36	double leak;
	37
	38	/* compute how much to leak */
13566fe3	39	leak = (bkt->avg * (double) delta_ns) / NANOSECONDS_PER_SECOND;
5ddfffbd BC	40
	41	/* make the bucket leak */
	42	bkt->level = MAX(bkt->level - leak, 0);
	43	}
	44
	45	/* Calculate the time delta since last leak and make proportionals leaks
	46	*
	47	* @now: the current timestamp in ns
	48	*/
	49	static void throttle_do_leak(ThrottleState *ts, int64_t now)
	50	{
	51	/* compute the time elapsed since the last leak */
	52	int64_t delta_ns = now - ts->previous_leak;
	53	int i;
	54
	55	ts->previous_leak = now;
	56
	57	if (delta_ns <= 0) {
	58	return;
	59	}
	60
	61	/* make each bucket leak */
	62	for (i = 0; i < BUCKETS_COUNT; i++) {
	63	throttle_leak_bucket(&ts->cfg.buckets[i], delta_ns);
	64	}
	65	}
	66
	67	/* do the real job of computing the time to wait
	68	*
	69	* @limit: the throttling limit
	70	* @extra: the number of operation to delay
	71	* @ret: the time to wait in ns
	72	*/
	73	static int64_t throttle_do_compute_wait(double limit, double extra)
	74	{
13566fe3	75	double wait = extra * NANOSECONDS_PER_SECOND;
5ddfffbd BC	76	wait /= limit;
	77	return wait;
	78	}
	79
	80	/* This function compute the wait time in ns that a leaky bucket should trigger
	81	*
	82	* @bkt: the leaky bucket we operate on
	83	* @ret: the resulting wait time in ns or 0 if the operation can go through
	84	*/
	85	int64_t throttle_compute_wait(LeakyBucket *bkt)
	86	{
	87	double extra; /* the number of extra units blocking the io */
	88
	89	if (!bkt->avg) {
	90	return 0;
	91	}
	92
	93	extra = bkt->level - bkt->max;
	94
	95	if (extra <= 0) {
	96	return 0;
	97	}
	98
	99	return throttle_do_compute_wait(bkt->avg, extra);
	100	}
	101
	102	/* This function compute the time that must be waited while this IO
	103	*
	104	* @is_write: true if the current IO is a write, false if it's a read
	105	* @ret: time to wait
	106	*/
	107	static int64_t throttle_compute_wait_for(ThrottleState *ts,
	108	bool is_write)
	109	{
	110	BucketType to_check[2][4] = { {THROTTLE_BPS_TOTAL,
	111	THROTTLE_OPS_TOTAL,
	112	THROTTLE_BPS_READ,
	113	THROTTLE_OPS_READ},
	114	{THROTTLE_BPS_TOTAL,
	115	THROTTLE_OPS_TOTAL,
	116	THROTTLE_BPS_WRITE,
	117	THROTTLE_OPS_WRITE}, };
	118	int64_t wait, max_wait = 0;
	119	int i;
	120
	121	for (i = 0; i < 4; i++) {
	122	BucketType index = to_check[is_write][i];
	123	wait = throttle_compute_wait(&ts->cfg.buckets[index]);
	124	if (wait > max_wait) {
	125	max_wait = wait;
	126	}
	127	}
	128
	129	return max_wait;
	130	}
	131
	132	/* compute the timer for this type of operation
	133	*
	134	* @is_write: the type of operation
	135	* @now: the current clock timestamp
	136	* @next_timestamp: the resulting timer
	137	* @ret: true if a timer must be set
	138	*/
	139	bool throttle_compute_timer(ThrottleState *ts,
140	bool is_write,
141	int64_t now,
142	int64_t *next_timestamp)
143	{
144	int64_t wait;
145
146	/* leak proportionally to the time elapsed */
147	throttle_do_leak(ts, now);
148
149	/* compute the wait time if any */
150	wait = throttle_compute_wait_for(ts, is_write);
151
152	/* if the code must wait compute when the next timer should fire */
153	if (wait) {
154	*next_timestamp = now + wait;
155	return true;
156	}
157
158	/* else no need to wait at all */
159	*next_timestamp = now;
160	return false;
161	}
162
13af91eb	163	/* Add timers to event loop */
0e5b0a2d BC	164	void throttle_timers_attach_aio_context(ThrottleTimers *tt,
0e5b0a2d BC	165	AioContext *new_context)
13af91eb	166	{
0e5b0a2d BC	167	tt->timers[0] = aio_timer_new(new_context, tt->clock_type, SCALE_NS,
	168	tt->read_timer_cb, tt->timer_opaque);
	169	tt->timers[1] = aio_timer_new(new_context, tt->clock_type, SCALE_NS,
	170	tt->write_timer_cb, tt->timer_opaque);
13af91eb SH	171	}
13af91eb SH	172
5ddfffbd	173	/* To be called first on the ThrottleState */
0e5b0a2d	174	void throttle_init(ThrottleState *ts)
5ddfffbd BC	175	{
5ddfffbd BC	176	memset(ts, 0, sizeof(ThrottleState));
0e5b0a2d BC	177	}
	178
	179	/* To be called first on the ThrottleTimers */
	180	void throttle_timers_init(ThrottleTimers *tt,
	181	AioContext *aio_context,
	182	QEMUClockType clock_type,
	183	QEMUTimerCB *read_timer_cb,
	184	QEMUTimerCB *write_timer_cb,
	185	void *timer_opaque)
	186	{
	187	memset(tt, 0, sizeof(ThrottleTimers));
5ddfffbd	188
0e5b0a2d BC	189	tt->clock_type = clock_type;
	190	tt->read_timer_cb = read_timer_cb;
	191	tt->write_timer_cb = write_timer_cb;
	192	tt->timer_opaque = timer_opaque;
	193	throttle_timers_attach_aio_context(tt, aio_context);
5ddfffbd BC	194	}
	195
	196	/* destroy a timer */
	197	static void throttle_timer_destroy(QEMUTimer **timer)
	198	{
	199	assert(*timer != NULL);
	200
	201	timer_del(*timer);
	202	timer_free(*timer);
	203	*timer = NULL;
	204	}
	205
13af91eb	206	/* Remove timers from event loop */
0e5b0a2d	207	void throttle_timers_detach_aio_context(ThrottleTimers *tt)
5ddfffbd BC	208	{
	209	int i;
	210
	211	for (i = 0; i < 2; i++) {
0e5b0a2d	212	throttle_timer_destroy(&tt->timers[i]);
5ddfffbd BC	213	}
	214	}
	215
0e5b0a2d BC	216	/* To be called last on the ThrottleTimers */
0e5b0a2d BC	217	void throttle_timers_destroy(ThrottleTimers *tt)
13af91eb	218	{
0e5b0a2d	219	throttle_timers_detach_aio_context(tt);
13af91eb SH	220	}
13af91eb SH	221
5ddfffbd	222	/* is any throttling timer configured */
0e5b0a2d	223	bool throttle_timers_are_initialized(ThrottleTimers *tt)
5ddfffbd	224	{
0e5b0a2d	225	if (tt->timers[0]) {
5ddfffbd BC	226	return true;
	227	}
	228
	229	return false;
	230	}
	231
	232	/* Does any throttling must be done
	233	*
	234	* @cfg: the throttling configuration to inspect
	235	* @ret: true if throttling must be done else false
	236	*/
	237	bool throttle_enabled(ThrottleConfig *cfg)
	238	{
	239	int i;
	240
	241	for (i = 0; i < BUCKETS_COUNT; i++) {
	242	if (cfg->buckets[i].avg > 0) {
	243	return true;
	244	}
	245	}
	246
	247	return false;
	248	}
	249
	250	/* return true if any two throttling parameters conflicts
	251	*
	252	* @cfg: the throttling configuration to inspect
	253	* @ret: true if any conflict detected else false
	254	*/
	255	bool throttle_conflicting(ThrottleConfig *cfg)
	256	{
	257	bool bps_flag, ops_flag;
	258	bool bps_max_flag, ops_max_flag;
	259
	260	bps_flag = cfg->buckets[THROTTLE_BPS_TOTAL].avg &&
	261	(cfg->buckets[THROTTLE_BPS_READ].avg \|\|
	262	cfg->buckets[THROTTLE_BPS_WRITE].avg);
	263
	264	ops_flag = cfg->buckets[THROTTLE_OPS_TOTAL].avg &&
	265	(cfg->buckets[THROTTLE_OPS_READ].avg \|\|
	266	cfg->buckets[THROTTLE_OPS_WRITE].avg);
	267
	268	bps_max_flag = cfg->buckets[THROTTLE_BPS_TOTAL].max &&
	269	(cfg->buckets[THROTTLE_BPS_READ].max \|\|
	270	cfg->buckets[THROTTLE_BPS_WRITE].max);
	271
	272	ops_max_flag = cfg->buckets[THROTTLE_OPS_TOTAL].max &&
	273	(cfg->buckets[THROTTLE_OPS_READ].max \|\|
	274	cfg->buckets[THROTTLE_OPS_WRITE].max);
	275
	276	return bps_flag \|\| ops_flag \|\| bps_max_flag \|\| ops_max_flag;
	277	}
	278
	279	/* check if a throttling configuration is valid
	280	* @cfg: the throttling configuration to inspect
	281	* @ret: true if valid else false
	282	*/
	283	bool throttle_is_valid(ThrottleConfig *cfg)
	284	{
	285	bool invalid = false;
	286	int i;
	287
	288	for (i = 0; i < BUCKETS_COUNT; i++) {
	289	if (cfg->buckets[i].avg < 0) {
290	invalid = true;
291	}
292	}
293
294	for (i = 0; i < BUCKETS_COUNT; i++) {
295	if (cfg->buckets[i].max < 0) {
296	invalid = true;
297	}
298	}
299
300	return !invalid;
301	}
302
ee2bdc33 SH	303	/* check if bps_max/iops_max is used without bps/iops
	304	* @cfg: the throttling configuration to inspect
	305	*/
	306	bool throttle_max_is_missing_limit(ThrottleConfig *cfg)
	307	{
	308	int i;
	309
	310	for (i = 0; i < BUCKETS_COUNT; i++) {
	311	if (cfg->buckets[i].max && !cfg->buckets[i].avg) {
	312	return true;
	313	}
	314	}
	315	return false;
	316	}
	317
5ddfffbd BC	318	/* fix bucket parameters */
	319	static void throttle_fix_bucket(LeakyBucket *bkt)
	320	{
	321	double min;
	322
	323	/* zero bucket level */
	324	bkt->level = 0;
	325
	326	/* The following is done to cope with the Linux CFQ block scheduler
	327	* which regroup reads and writes by block of 100ms in the guest.
	328	* When they are two process one making reads and one making writes cfq
	329	* make a pattern looking like the following:
	330	* WWWWWWWWWWWRRRRRRRRRRRRRRWWWWWWWWWWWWWwRRRRRRRRRRRRRRRRR
	331	* Having a max burst value of 100ms of the average will help smooth the
	332	* throttling
	333	*/
	334	min = bkt->avg / 10;
	335	if (bkt->avg && !bkt->max) {
	336	bkt->max = min;
	337	}
	338	}
	339
	340	/* take care of canceling a timer */
	341	static void throttle_cancel_timer(QEMUTimer *timer)
	342	{
	343	assert(timer != NULL);
	344
	345	timer_del(timer);
	346	}
	347
	348	/* Used to configure the throttle
	349	*
	350	* @ts: the throttle state we are working on
0e5b0a2d	351	* @tt: the throttle timers we use in this aio context
5ddfffbd BC	352	* @cfg: the config to set
5ddfffbd BC	353	*/
0e5b0a2d BC	354	void throttle_config(ThrottleState *ts,
	355	ThrottleTimers *tt,
	356	ThrottleConfig *cfg)
5ddfffbd BC	357	{
	358	int i;
	359
	360	ts->cfg = *cfg;
	361
	362	for (i = 0; i < BUCKETS_COUNT; i++) {
	363	throttle_fix_bucket(&ts->cfg.buckets[i]);
	364	}
	365
0e5b0a2d	366	ts->previous_leak = qemu_clock_get_ns(tt->clock_type);
5ddfffbd BC	367
5ddfffbd BC	368	for (i = 0; i < 2; i++) {
0e5b0a2d	369	throttle_cancel_timer(tt->timers[i]);
5ddfffbd BC	370	}
	371	}
	372
	373	/* used to get config
	374	*
	375	* @ts: the throttle state we are working on
	376	* @cfg: the config to write
	377	*/
	378	void throttle_get_config(ThrottleState ts, ThrottleConfig cfg)
	379	{
	380	*cfg = ts->cfg;
	381	}
	382
	383
	384	/* Schedule the read or write timer if needed
	385	*
	386	* NOTE: this function is not unit tested due to it's usage of timer_mod
	387	*
0e5b0a2d	388	* @tt: the timers structure
5ddfffbd BC	389	* @is_write: the type of operation (read/write)
	390	* @ret: true if the timer has been scheduled else false
	391	*/
0e5b0a2d BC	392	bool throttle_schedule_timer(ThrottleState *ts,
	393	ThrottleTimers *tt,
	394	bool is_write)
5ddfffbd	395	{
0e5b0a2d	396	int64_t now = qemu_clock_get_ns(tt->clock_type);
5ddfffbd BC	397	int64_t next_timestamp;
	398	bool must_wait;
	399
	400	must_wait = throttle_compute_timer(ts,
	401	is_write,
	402	now,
	403	&next_timestamp);
	404
	405	/* request not throttled */
	406	if (!must_wait) {
	407	return false;
	408	}
	409
	410	/* request throttled and timer pending -> do nothing */
0e5b0a2d	411	if (timer_pending(tt->timers[is_write])) {
5ddfffbd BC	412	return true;
	413	}
	414
	415	/* request throttled and timer not pending -> arm timer */
0e5b0a2d	416	timer_mod(tt->timers[is_write], next_timestamp);
5ddfffbd BC	417	return true;
	418	}
	419
	420	/* do the accounting for this operation
	421	*
	422	* @is_write: the type of operation (read/write)
	423	* @size: the size of the operation
	424	*/
	425	void throttle_account(ThrottleState *ts, bool is_write, uint64_t size)
	426	{
	427	double units = 1.0;
	428
	429	/* if cfg.op_size is defined and smaller than size we compute unit count */
	430	if (ts->cfg.op_size && size > ts->cfg.op_size) {
	431	units = (double) size / ts->cfg.op_size;
	432	}
	433
	434	ts->cfg.buckets[THROTTLE_BPS_TOTAL].level += size;
	435	ts->cfg.buckets[THROTTLE_OPS_TOTAL].level += units;
	436
	437	if (is_write) {
	438	ts->cfg.buckets[THROTTLE_BPS_WRITE].level += size;
	439	ts->cfg.buckets[THROTTLE_OPS_WRITE].level += units;
	440	} else {
	441	ts->cfg.buckets[THROTTLE_BPS_READ].level += size;
	442	ts->cfg.buckets[THROTTLE_OPS_READ].level += units;
	443	}
	444	}
	445