/*
* 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/osdep.h"
#include "qapi/error.h"
#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);
/* if we allow bursts for more than one second we also need to
* keep track of bkt->burst_level so the bkt->max goal per second
* is attained */
if (bkt->burst_length > 1) {
leak = (bkt->max * (double) delta_ns) / NANOSECONDS_PER_SECOND;
bkt->burst_level = MAX(bkt->burst_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 */
double bucket_size; /* I/O before throttling to bkt->avg */
double burst_bucket_size; /* Before throttling to bkt->max */
if (!bkt->avg) {
return 0;
}
if (!bkt->max) {
/* If bkt->max is 0 we still want to allow short bursts of I/O
* from the guest, otherwise every other request will be throttled
* and performance will suffer considerably. */
bucket_size = (double) bkt->avg / 10;
burst_bucket_size = 0;
} else {
/* If we have a burst limit then we have to wait until all I/O
* at burst rate has finished before throttling to bkt->avg */
bucket_size = bkt->max * bkt->burst_length;
burst_bucket_size = (double) bkt->max / 10;
}
/* If the main bucket is full then we have to wait */
extra = bkt->level - bucket_size;
if (extra > 0) {
return throttle_do_compute_wait(bkt->avg, extra);
}
/* If the main bucket is not full yet we still have to check the
* burst bucket in order to enforce the burst limit */
if (bkt->burst_length > 1) {
extra = bkt->burst_level - burst_bucket_size;
if (extra > 0) {
return throttle_do_compute_wait(bkt->max, extra);
}
}
return 0;
}
/* 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
*/
static 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);
}
/*
* Initialize the ThrottleConfig structure to a valid state
* @cfg: the config to initialize
*/
void throttle_config_init(ThrottleConfig *cfg)
{
unsigned i;
memset(cfg, 0, sizeof(*cfg));
for (i = 0; i < BUCKETS_COUNT; i++) {
cfg->buckets[i].burst_length = 1;
}
}
/* To be called first on the ThrottleState */
void throttle_init(ThrottleState *ts)
{
memset(ts, 0, sizeof(ThrottleState));
throttle_config_init(&ts->cfg);
}
/* 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;
}
/* check if a throttling configuration is valid
* @cfg: the throttling configuration to inspect
* @ret: true if valid else false
* @errp: error object
*/
bool throttle_is_valid(ThrottleConfig *cfg, Error **errp)
{
int i;
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);
if (bps_flag || ops_flag || bps_max_flag || ops_max_flag) {
error_setg(errp, "bps/iops/max total values and read/write values"
" cannot be used at the same time");
return false;
}
if (cfg->op_size &&
!cfg->buckets[THROTTLE_OPS_TOTAL].avg &&
!cfg->buckets[THROTTLE_OPS_READ].avg &&
!cfg->buckets[THROTTLE_OPS_WRITE].avg) {
error_setg(errp, "iops size requires an iops value to be set");
return false;
}
for (i = 0; i < BUCKETS_COUNT; i++) {
LeakyBucket *bkt = &cfg->buckets[i];
if (bkt->avg > THROTTLE_VALUE_MAX || bkt->max > THROTTLE_VALUE_MAX) {
error_setg(errp, "bps/iops/max values must be within [0, %lld]",
THROTTLE_VALUE_MAX);
return false;
}
if (!bkt->burst_length) {
error_setg(errp, "the burst length cannot be 0");
return false;
}
if (bkt->burst_length > 1 && !bkt->max) {
error_setg(errp, "burst length set without burst rate");
return false;
}
if (bkt->max && bkt->burst_length > THROTTLE_VALUE_MAX / bkt->max) {
error_setg(errp, "burst length too high for this burst rate");
return false;
}
if (bkt->max && !bkt->avg) {
error_setg(errp, "bps_max/iops_max require corresponding"
" bps/iops values");
return false;
}
if (bkt->max && bkt->max < bkt->avg) {
error_setg(errp, "bps_max/iops_max cannot be lower than bps/iops");
return false;
}
}
return true;
}
/* Used to configure the throttle
*
* @ts: the throttle state we are working on
* @clock_type: the group's clock_type
* @cfg: the config to set
*/
void throttle_config(ThrottleState *ts,
QEMUClockType clock_type,
ThrottleConfig *cfg)
{
int i;
ts->cfg = *cfg;
/* Zero bucket level */
for (i = 0; i < BUCKETS_COUNT; i++) {
ts->cfg.buckets[i].level = 0;
ts->cfg.buckets[i].burst_level = 0;
}
ts->previous_leak = qemu_clock_get_ns(clock_type);
}
/* 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)
{
const BucketType bucket_types_size[2][2] = {
{ THROTTLE_BPS_TOTAL, THROTTLE_BPS_READ },
{ THROTTLE_BPS_TOTAL, THROTTLE_BPS_WRITE }
};
const BucketType bucket_types_units[2][2] = {
{ THROTTLE_OPS_TOTAL, THROTTLE_OPS_READ },
{ THROTTLE_OPS_TOTAL, THROTTLE_OPS_WRITE }
};
double units = 1.0;
unsigned i;
/* 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;
}
for (i = 0; i < 2; i++) {
LeakyBucket *bkt;
bkt = &ts->cfg.buckets[bucket_types_size[is_write][i]];
bkt->level += size;
if (bkt->burst_length > 1) {
bkt->burst_level += size;
}
bkt = &ts->cfg.buckets[bucket_types_units[is_write][i]];
bkt->level += units;
if (bkt->burst_length > 1) {
bkt->burst_level += units;
}
}
}
