qemu/block/throttle-groups.c
Alberto Garcia 5ac724184c throttle: Check for pending requests in throttle_group_unregister_bs()
throttle_group_unregister_bs() removes a BlockDriverState from its
throttling group and destroys the timers. This means that there must
be no pending throttled requests at that point (because it would be
impossible to complete them), so the caller has to drain them first.

At the moment throttle_group_unregister_bs() is only called from
bdrv_io_limits_disable(), which already takes care of draining the
requests, so there's nothing to worry about, but this patch makes
this invariant explicit in the documentation and adds the relevant
assertions.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2015-11-11 16:25:47 +01:00

483 lines
15 KiB
C

/*
* QEMU block throttling group infrastructure
*
* Copyright (C) Nodalink, EURL. 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 "block/throttle-groups.h"
#include "qemu/queue.h"
#include "qemu/thread.h"
#include "sysemu/qtest.h"
/* The ThrottleGroup structure (with its ThrottleState) is shared
* among different BlockDriverState and it's independent from
* AioContext, so in order to use it from different threads it needs
* its own locking.
*
* This locking is however handled internally in this file, so it's
* transparent to outside users.
*
* The whole ThrottleGroup structure is private and invisible to
* outside users, that only use it through its ThrottleState.
*
* In addition to the ThrottleGroup structure, BlockDriverState has
* fields that need to be accessed by other members of the group and
* therefore also need to be protected by this lock. Once a BDS is
* registered in a group those fields can be accessed by other threads
* any time.
*
* Again, all this is handled internally and is mostly transparent to
* the outside. The 'throttle_timers' field however has an additional
* constraint because it may be temporarily invalid (see for example
* bdrv_set_aio_context()). Therefore in this file a thread will
* access some other BDS's timers only after verifying that that BDS
* has throttled requests in the queue.
*/
typedef struct ThrottleGroup {
char *name; /* This is constant during the lifetime of the group */
QemuMutex lock; /* This lock protects the following four fields */
ThrottleState ts;
QLIST_HEAD(, BlockDriverState) head;
BlockDriverState *tokens[2];
bool any_timer_armed[2];
/* These two are protected by the global throttle_groups_lock */
unsigned refcount;
QTAILQ_ENTRY(ThrottleGroup) list;
} ThrottleGroup;
static QemuMutex throttle_groups_lock;
static QTAILQ_HEAD(, ThrottleGroup) throttle_groups =
QTAILQ_HEAD_INITIALIZER(throttle_groups);
/* Increments the reference count of a ThrottleGroup given its name.
*
* If no ThrottleGroup is found with the given name a new one is
* created.
*
* @name: the name of the ThrottleGroup
* @ret: the ThrottleState member of the ThrottleGroup
*/
ThrottleState *throttle_group_incref(const char *name)
{
ThrottleGroup *tg = NULL;
ThrottleGroup *iter;
qemu_mutex_lock(&throttle_groups_lock);
/* Look for an existing group with that name */
QTAILQ_FOREACH(iter, &throttle_groups, list) {
if (!strcmp(name, iter->name)) {
tg = iter;
break;
}
}
/* Create a new one if not found */
if (!tg) {
tg = g_new0(ThrottleGroup, 1);
tg->name = g_strdup(name);
qemu_mutex_init(&tg->lock);
throttle_init(&tg->ts);
QLIST_INIT(&tg->head);
QTAILQ_INSERT_TAIL(&throttle_groups, tg, list);
}
tg->refcount++;
qemu_mutex_unlock(&throttle_groups_lock);
return &tg->ts;
}
/* Decrease the reference count of a ThrottleGroup.
*
* When the reference count reaches zero the ThrottleGroup is
* destroyed.
*
* @ts: The ThrottleGroup to unref, given by its ThrottleState member
*/
void throttle_group_unref(ThrottleState *ts)
{
ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
qemu_mutex_lock(&throttle_groups_lock);
if (--tg->refcount == 0) {
QTAILQ_REMOVE(&throttle_groups, tg, list);
qemu_mutex_destroy(&tg->lock);
g_free(tg->name);
g_free(tg);
}
qemu_mutex_unlock(&throttle_groups_lock);
}
/* Get the name from a BlockDriverState's ThrottleGroup. The name (and
* the pointer) is guaranteed to remain constant during the lifetime
* of the group.
*
* @bs: a BlockDriverState that is member of a throttling group
* @ret: the name of the group.
*/
const char *throttle_group_get_name(BlockDriverState *bs)
{
ThrottleGroup *tg = container_of(bs->throttle_state, ThrottleGroup, ts);
return tg->name;
}
/* Return the next BlockDriverState in the round-robin sequence,
* simulating a circular list.
*
* This assumes that tg->lock is held.
*
* @bs: the current BlockDriverState
* @ret: the next BlockDriverState in the sequence
*/
static BlockDriverState *throttle_group_next_bs(BlockDriverState *bs)
{
ThrottleState *ts = bs->throttle_state;
ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
BlockDriverState *next = QLIST_NEXT(bs, round_robin);
if (!next) {
return QLIST_FIRST(&tg->head);
}
return next;
}
/* Return the next BlockDriverState in the round-robin sequence with
* pending I/O requests.
*
* This assumes that tg->lock is held.
*
* @bs: the current BlockDriverState
* @is_write: the type of operation (read/write)
* @ret: the next BlockDriverState with pending requests, or bs
* if there is none.
*/
static BlockDriverState *next_throttle_token(BlockDriverState *bs,
bool is_write)
{
ThrottleGroup *tg = container_of(bs->throttle_state, ThrottleGroup, ts);
BlockDriverState *token, *start;
start = token = tg->tokens[is_write];
/* get next bs round in round robin style */
token = throttle_group_next_bs(token);
while (token != start && !token->pending_reqs[is_write]) {
token = throttle_group_next_bs(token);
}
/* If no IO are queued for scheduling on the next round robin token
* then decide the token is the current bs because chances are
* the current bs get the current request queued.
*/
if (token == start && !token->pending_reqs[is_write]) {
token = bs;
}
return token;
}
/* Check if the next I/O request for a BlockDriverState needs to be
* throttled or not. If there's no timer set in this group, set one
* and update the token accordingly.
*
* This assumes that tg->lock is held.
*
* @bs: the current BlockDriverState
* @is_write: the type of operation (read/write)
* @ret: whether the I/O request needs to be throttled or not
*/
static bool throttle_group_schedule_timer(BlockDriverState *bs,
bool is_write)
{
ThrottleState *ts = bs->throttle_state;
ThrottleTimers *tt = &bs->throttle_timers;
ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
bool must_wait;
/* Check if any of the timers in this group is already armed */
if (tg->any_timer_armed[is_write]) {
return true;
}
must_wait = throttle_schedule_timer(ts, tt, is_write);
/* If a timer just got armed, set bs as the current token */
if (must_wait) {
tg->tokens[is_write] = bs;
tg->any_timer_armed[is_write] = true;
}
return must_wait;
}
/* Look for the next pending I/O request and schedule it.
*
* This assumes that tg->lock is held.
*
* @bs: the current BlockDriverState
* @is_write: the type of operation (read/write)
*/
static void schedule_next_request(BlockDriverState *bs, bool is_write)
{
ThrottleGroup *tg = container_of(bs->throttle_state, ThrottleGroup, ts);
bool must_wait;
BlockDriverState *token;
/* Check if there's any pending request to schedule next */
token = next_throttle_token(bs, is_write);
if (!token->pending_reqs[is_write]) {
return;
}
/* Set a timer for the request if it needs to be throttled */
must_wait = throttle_group_schedule_timer(token, is_write);
/* If it doesn't have to wait, queue it for immediate execution */
if (!must_wait) {
/* Give preference to requests from the current bs */
if (qemu_in_coroutine() &&
qemu_co_queue_next(&bs->throttled_reqs[is_write])) {
token = bs;
} else {
ThrottleTimers *tt = &token->throttle_timers;
int64_t now = qemu_clock_get_ns(tt->clock_type);
timer_mod(tt->timers[is_write], now + 1);
tg->any_timer_armed[is_write] = true;
}
tg->tokens[is_write] = token;
}
}
/* Check if an I/O request needs to be throttled, wait and set a timer
* if necessary, and schedule the next request using a round robin
* algorithm.
*
* @bs: the current BlockDriverState
* @bytes: the number of bytes for this I/O
* @is_write: the type of operation (read/write)
*/
void coroutine_fn throttle_group_co_io_limits_intercept(BlockDriverState *bs,
unsigned int bytes,
bool is_write)
{
bool must_wait;
BlockDriverState *token;
ThrottleGroup *tg = container_of(bs->throttle_state, ThrottleGroup, ts);
qemu_mutex_lock(&tg->lock);
/* First we check if this I/O has to be throttled. */
token = next_throttle_token(bs, is_write);
must_wait = throttle_group_schedule_timer(token, is_write);
/* Wait if there's a timer set or queued requests of this type */
if (must_wait || bs->pending_reqs[is_write]) {
bs->pending_reqs[is_write]++;
qemu_mutex_unlock(&tg->lock);
qemu_co_queue_wait(&bs->throttled_reqs[is_write]);
qemu_mutex_lock(&tg->lock);
bs->pending_reqs[is_write]--;
}
/* The I/O will be executed, so do the accounting */
throttle_account(bs->throttle_state, is_write, bytes);
/* Schedule the next request */
schedule_next_request(bs, is_write);
qemu_mutex_unlock(&tg->lock);
}
/* Update the throttle configuration for a particular group. Similar
* to throttle_config(), but guarantees atomicity within the
* throttling group.
*
* @bs: a BlockDriverState that is member of the group
* @cfg: the configuration to set
*/
void throttle_group_config(BlockDriverState *bs, ThrottleConfig *cfg)
{
ThrottleTimers *tt = &bs->throttle_timers;
ThrottleState *ts = bs->throttle_state;
ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
qemu_mutex_lock(&tg->lock);
/* throttle_config() cancels the timers */
if (timer_pending(tt->timers[0])) {
tg->any_timer_armed[0] = false;
}
if (timer_pending(tt->timers[1])) {
tg->any_timer_armed[1] = false;
}
throttle_config(ts, tt, cfg);
qemu_mutex_unlock(&tg->lock);
}
/* Get the throttle configuration from a particular group. Similar to
* throttle_get_config(), but guarantees atomicity within the
* throttling group.
*
* @bs: a BlockDriverState that is member of the group
* @cfg: the configuration will be written here
*/
void throttle_group_get_config(BlockDriverState *bs, ThrottleConfig *cfg)
{
ThrottleState *ts = bs->throttle_state;
ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
qemu_mutex_lock(&tg->lock);
throttle_get_config(ts, cfg);
qemu_mutex_unlock(&tg->lock);
}
/* ThrottleTimers callback. This wakes up a request that was waiting
* because it had been throttled.
*
* @bs: the BlockDriverState whose request had been throttled
* @is_write: the type of operation (read/write)
*/
static void timer_cb(BlockDriverState *bs, bool is_write)
{
ThrottleState *ts = bs->throttle_state;
ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
bool empty_queue;
/* The timer has just been fired, so we can update the flag */
qemu_mutex_lock(&tg->lock);
tg->any_timer_armed[is_write] = false;
qemu_mutex_unlock(&tg->lock);
/* Run the request that was waiting for this timer */
empty_queue = !qemu_co_enter_next(&bs->throttled_reqs[is_write]);
/* If the request queue was empty then we have to take care of
* scheduling the next one */
if (empty_queue) {
qemu_mutex_lock(&tg->lock);
schedule_next_request(bs, is_write);
qemu_mutex_unlock(&tg->lock);
}
}
static void read_timer_cb(void *opaque)
{
timer_cb(opaque, false);
}
static void write_timer_cb(void *opaque)
{
timer_cb(opaque, true);
}
/* Register a BlockDriverState in the throttling group, also
* initializing its timers and updating its throttle_state pointer to
* point to it. If a throttling group with that name does not exist
* yet, it will be created.
*
* @bs: the BlockDriverState to insert
* @groupname: the name of the group
*/
void throttle_group_register_bs(BlockDriverState *bs, const char *groupname)
{
int i;
ThrottleState *ts = throttle_group_incref(groupname);
ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
int clock_type = QEMU_CLOCK_REALTIME;
if (qtest_enabled()) {
/* For testing block IO throttling only */
clock_type = QEMU_CLOCK_VIRTUAL;
}
bs->throttle_state = ts;
qemu_mutex_lock(&tg->lock);
/* If the ThrottleGroup is new set this BlockDriverState as the token */
for (i = 0; i < 2; i++) {
if (!tg->tokens[i]) {
tg->tokens[i] = bs;
}
}
QLIST_INSERT_HEAD(&tg->head, bs, round_robin);
throttle_timers_init(&bs->throttle_timers,
bdrv_get_aio_context(bs),
clock_type,
read_timer_cb,
write_timer_cb,
bs);
qemu_mutex_unlock(&tg->lock);
}
/* Unregister a BlockDriverState from its group, removing it from the
* list, destroying the timers and setting the throttle_state pointer
* to NULL.
*
* The BlockDriverState must not have pending throttled requests, so
* the caller has to drain them first.
*
* The group will be destroyed if it's empty after this operation.
*
* @bs: the BlockDriverState to remove
*/
void throttle_group_unregister_bs(BlockDriverState *bs)
{
ThrottleGroup *tg = container_of(bs->throttle_state, ThrottleGroup, ts);
int i;
assert(bs->pending_reqs[0] == 0 && bs->pending_reqs[1] == 0);
assert(qemu_co_queue_empty(&bs->throttled_reqs[0]));
assert(qemu_co_queue_empty(&bs->throttled_reqs[1]));
qemu_mutex_lock(&tg->lock);
for (i = 0; i < 2; i++) {
if (tg->tokens[i] == bs) {
BlockDriverState *token = throttle_group_next_bs(bs);
/* Take care of the case where this is the last bs in the group */
if (token == bs) {
token = NULL;
}
tg->tokens[i] = token;
}
}
/* remove the current bs from the list */
QLIST_REMOVE(bs, round_robin);
throttle_timers_destroy(&bs->throttle_timers);
qemu_mutex_unlock(&tg->lock);
throttle_group_unref(&tg->ts);
bs->throttle_state = NULL;
}
static void throttle_groups_init(void)
{
qemu_mutex_init(&throttle_groups_lock);
}
block_init(throttle_groups_init);