throttle_config() cancels the timers of the calling BlockBackend. This doesn't make sense because other BlockBackends in the group remain untouched. There's no need to cancel the timers in the one specific BlockBackend so let's not do that. Throttled requests will run as scheduled and future requests will follow the new configuration. This also allows a throttle group's configuration to be changed even when it has no members. Signed-off-by: Manos Pitsidianakis <el13635@mail.ntua.gr> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
568 lines
18 KiB
C
568 lines
18 KiB
C
/*
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* QEMU block throttling group infrastructure
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*
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* Copyright (C) Nodalink, EURL. 2014
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* Copyright (C) Igalia, S.L. 2015
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*
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* Authors:
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* Benoît Canet <benoit.canet@nodalink.com>
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* Alberto Garcia <berto@igalia.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 or
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* (at your option) version 3 of the License.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, see <http://www.gnu.org/licenses/>.
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*/
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#include "qemu/osdep.h"
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#include "sysemu/block-backend.h"
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#include "block/throttle-groups.h"
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#include "qemu/queue.h"
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#include "qemu/thread.h"
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#include "sysemu/qtest.h"
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/* The ThrottleGroup structure (with its ThrottleState) is shared
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* among different BlockBackends and it's independent from
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* AioContext, so in order to use it from different threads it needs
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* its own locking.
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*
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* This locking is however handled internally in this file, so it's
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* transparent to outside users.
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*
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* The whole ThrottleGroup structure is private and invisible to
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* outside users, that only use it through its ThrottleState.
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*
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* In addition to the ThrottleGroup structure, BlockBackendPublic has
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* fields that need to be accessed by other members of the group and
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* therefore also need to be protected by this lock. Once a
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* BlockBackend is registered in a group those fields can be accessed
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* by other threads any time.
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*
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* Again, all this is handled internally and is mostly transparent to
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* the outside. The 'throttle_timers' field however has an additional
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* constraint because it may be temporarily invalid (see for example
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* blk_set_aio_context()). Therefore in this file a thread will
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* access some other BlockBackend's timers only after verifying that
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* that BlockBackend has throttled requests in the queue.
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*/
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typedef struct ThrottleGroup {
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char *name; /* This is constant during the lifetime of the group */
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QemuMutex lock; /* This lock protects the following four fields */
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ThrottleState ts;
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QLIST_HEAD(, BlockBackendPublic) head;
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BlockBackend *tokens[2];
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bool any_timer_armed[2];
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QEMUClockType clock_type;
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/* These two are protected by the global throttle_groups_lock */
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unsigned refcount;
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QTAILQ_ENTRY(ThrottleGroup) list;
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} ThrottleGroup;
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static QemuMutex throttle_groups_lock;
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static QTAILQ_HEAD(, ThrottleGroup) throttle_groups =
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QTAILQ_HEAD_INITIALIZER(throttle_groups);
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/* Increments the reference count of a ThrottleGroup given its name.
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*
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* If no ThrottleGroup is found with the given name a new one is
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* created.
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*
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* @name: the name of the ThrottleGroup
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* @ret: the ThrottleState member of the ThrottleGroup
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*/
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ThrottleState *throttle_group_incref(const char *name)
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{
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ThrottleGroup *tg = NULL;
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ThrottleGroup *iter;
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qemu_mutex_lock(&throttle_groups_lock);
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/* Look for an existing group with that name */
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QTAILQ_FOREACH(iter, &throttle_groups, list) {
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if (!strcmp(name, iter->name)) {
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tg = iter;
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break;
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}
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}
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/* Create a new one if not found */
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if (!tg) {
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tg = g_new0(ThrottleGroup, 1);
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tg->name = g_strdup(name);
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tg->clock_type = QEMU_CLOCK_REALTIME;
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if (qtest_enabled()) {
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/* For testing block IO throttling only */
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tg->clock_type = QEMU_CLOCK_VIRTUAL;
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}
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qemu_mutex_init(&tg->lock);
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throttle_init(&tg->ts);
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QLIST_INIT(&tg->head);
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QTAILQ_INSERT_TAIL(&throttle_groups, tg, list);
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}
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tg->refcount++;
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qemu_mutex_unlock(&throttle_groups_lock);
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return &tg->ts;
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}
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/* Decrease the reference count of a ThrottleGroup.
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*
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* When the reference count reaches zero the ThrottleGroup is
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* destroyed.
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*
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* @ts: The ThrottleGroup to unref, given by its ThrottleState member
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*/
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void throttle_group_unref(ThrottleState *ts)
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{
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ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
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qemu_mutex_lock(&throttle_groups_lock);
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if (--tg->refcount == 0) {
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QTAILQ_REMOVE(&throttle_groups, tg, list);
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qemu_mutex_destroy(&tg->lock);
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g_free(tg->name);
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g_free(tg);
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}
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qemu_mutex_unlock(&throttle_groups_lock);
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}
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/* Get the name from a BlockBackend's ThrottleGroup. The name (and the pointer)
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* is guaranteed to remain constant during the lifetime of the group.
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*
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* @blk: a BlockBackend that is member of a throttling group
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* @ret: the name of the group.
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*/
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const char *throttle_group_get_name(BlockBackend *blk)
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{
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BlockBackendPublic *blkp = blk_get_public(blk);
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ThrottleGroup *tg = container_of(blkp->throttle_state, ThrottleGroup, ts);
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return tg->name;
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}
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/* Return the next BlockBackend in the round-robin sequence, simulating a
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* circular list.
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*
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* This assumes that tg->lock is held.
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*
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* @blk: the current BlockBackend
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* @ret: the next BlockBackend in the sequence
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*/
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static BlockBackend *throttle_group_next_blk(BlockBackend *blk)
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{
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BlockBackendPublic *blkp = blk_get_public(blk);
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ThrottleState *ts = blkp->throttle_state;
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ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
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BlockBackendPublic *next = QLIST_NEXT(blkp, round_robin);
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if (!next) {
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next = QLIST_FIRST(&tg->head);
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}
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return blk_by_public(next);
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}
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/*
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* Return whether a BlockBackend has pending requests.
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*
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* This assumes that tg->lock is held.
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*
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* @blk: the BlockBackend
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* @is_write: the type of operation (read/write)
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* @ret: whether the BlockBackend has pending requests.
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*/
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static inline bool blk_has_pending_reqs(BlockBackend *blk,
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bool is_write)
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{
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const BlockBackendPublic *blkp = blk_get_public(blk);
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return blkp->pending_reqs[is_write];
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}
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/* Return the next BlockBackend in the round-robin sequence with pending I/O
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* requests.
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*
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* This assumes that tg->lock is held.
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*
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* @blk: the current BlockBackend
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* @is_write: the type of operation (read/write)
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* @ret: the next BlockBackend with pending requests, or blk if there is
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* none.
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*/
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static BlockBackend *next_throttle_token(BlockBackend *blk, bool is_write)
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{
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BlockBackendPublic *blkp = blk_get_public(blk);
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ThrottleGroup *tg = container_of(blkp->throttle_state, ThrottleGroup, ts);
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BlockBackend *token, *start;
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start = token = tg->tokens[is_write];
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/* get next bs round in round robin style */
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token = throttle_group_next_blk(token);
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while (token != start && !blk_has_pending_reqs(token, is_write)) {
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token = throttle_group_next_blk(token);
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}
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/* If no IO are queued for scheduling on the next round robin token
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* then decide the token is the current bs because chances are
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* the current bs get the current request queued.
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*/
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if (token == start && !blk_has_pending_reqs(token, is_write)) {
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token = blk;
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}
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/* Either we return the original BB, or one with pending requests */
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assert(token == blk || blk_has_pending_reqs(token, is_write));
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return token;
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}
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/* Check if the next I/O request for a BlockBackend needs to be throttled or
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* not. If there's no timer set in this group, set one and update the token
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* accordingly.
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*
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* This assumes that tg->lock is held.
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*
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* @blk: the current BlockBackend
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* @is_write: the type of operation (read/write)
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* @ret: whether the I/O request needs to be throttled or not
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*/
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static bool throttle_group_schedule_timer(BlockBackend *blk, bool is_write)
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{
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BlockBackendPublic *blkp = blk_get_public(blk);
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ThrottleState *ts = blkp->throttle_state;
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ThrottleTimers *tt = &blkp->throttle_timers;
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ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
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bool must_wait;
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if (atomic_read(&blkp->io_limits_disabled)) {
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return false;
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}
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/* Check if any of the timers in this group is already armed */
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if (tg->any_timer_armed[is_write]) {
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return true;
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}
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must_wait = throttle_schedule_timer(ts, tt, is_write);
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/* If a timer just got armed, set blk as the current token */
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if (must_wait) {
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tg->tokens[is_write] = blk;
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tg->any_timer_armed[is_write] = true;
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}
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return must_wait;
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}
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/* Start the next pending I/O request for a BlockBackend. Return whether
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* any request was actually pending.
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*
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* @blk: the current BlockBackend
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* @is_write: the type of operation (read/write)
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*/
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static bool coroutine_fn throttle_group_co_restart_queue(BlockBackend *blk,
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bool is_write)
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{
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BlockBackendPublic *blkp = blk_get_public(blk);
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bool ret;
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qemu_co_mutex_lock(&blkp->throttled_reqs_lock);
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ret = qemu_co_queue_next(&blkp->throttled_reqs[is_write]);
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qemu_co_mutex_unlock(&blkp->throttled_reqs_lock);
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return ret;
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}
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/* Look for the next pending I/O request and schedule it.
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*
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* This assumes that tg->lock is held.
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*
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* @blk: the current BlockBackend
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* @is_write: the type of operation (read/write)
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*/
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static void schedule_next_request(BlockBackend *blk, bool is_write)
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{
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BlockBackendPublic *blkp = blk_get_public(blk);
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ThrottleGroup *tg = container_of(blkp->throttle_state, ThrottleGroup, ts);
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bool must_wait;
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BlockBackend *token;
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/* Check if there's any pending request to schedule next */
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token = next_throttle_token(blk, is_write);
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if (!blk_has_pending_reqs(token, is_write)) {
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return;
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}
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/* Set a timer for the request if it needs to be throttled */
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must_wait = throttle_group_schedule_timer(token, is_write);
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/* If it doesn't have to wait, queue it for immediate execution */
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if (!must_wait) {
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/* Give preference to requests from the current blk */
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if (qemu_in_coroutine() &&
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throttle_group_co_restart_queue(blk, is_write)) {
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token = blk;
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} else {
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ThrottleTimers *tt = &blk_get_public(token)->throttle_timers;
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int64_t now = qemu_clock_get_ns(tg->clock_type);
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timer_mod(tt->timers[is_write], now);
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tg->any_timer_armed[is_write] = true;
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}
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tg->tokens[is_write] = token;
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}
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}
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/* Check if an I/O request needs to be throttled, wait and set a timer
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* if necessary, and schedule the next request using a round robin
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* algorithm.
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*
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* @blk: the current BlockBackend
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* @bytes: the number of bytes for this I/O
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* @is_write: the type of operation (read/write)
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*/
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void coroutine_fn throttle_group_co_io_limits_intercept(BlockBackend *blk,
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unsigned int bytes,
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bool is_write)
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{
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bool must_wait;
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BlockBackend *token;
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BlockBackendPublic *blkp = blk_get_public(blk);
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ThrottleGroup *tg = container_of(blkp->throttle_state, ThrottleGroup, ts);
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qemu_mutex_lock(&tg->lock);
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/* First we check if this I/O has to be throttled. */
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token = next_throttle_token(blk, is_write);
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must_wait = throttle_group_schedule_timer(token, is_write);
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/* Wait if there's a timer set or queued requests of this type */
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if (must_wait || blkp->pending_reqs[is_write]) {
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blkp->pending_reqs[is_write]++;
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qemu_mutex_unlock(&tg->lock);
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qemu_co_mutex_lock(&blkp->throttled_reqs_lock);
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qemu_co_queue_wait(&blkp->throttled_reqs[is_write],
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&blkp->throttled_reqs_lock);
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qemu_co_mutex_unlock(&blkp->throttled_reqs_lock);
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qemu_mutex_lock(&tg->lock);
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blkp->pending_reqs[is_write]--;
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}
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/* The I/O will be executed, so do the accounting */
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throttle_account(blkp->throttle_state, is_write, bytes);
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/* Schedule the next request */
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schedule_next_request(blk, is_write);
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qemu_mutex_unlock(&tg->lock);
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}
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typedef struct {
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BlockBackend *blk;
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bool is_write;
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} RestartData;
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static void coroutine_fn throttle_group_restart_queue_entry(void *opaque)
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{
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RestartData *data = opaque;
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BlockBackend *blk = data->blk;
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bool is_write = data->is_write;
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BlockBackendPublic *blkp = blk_get_public(blk);
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ThrottleGroup *tg = container_of(blkp->throttle_state, ThrottleGroup, ts);
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bool empty_queue;
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empty_queue = !throttle_group_co_restart_queue(blk, is_write);
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/* If the request queue was empty then we have to take care of
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* scheduling the next one */
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if (empty_queue) {
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qemu_mutex_lock(&tg->lock);
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schedule_next_request(blk, is_write);
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qemu_mutex_unlock(&tg->lock);
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}
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}
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static void throttle_group_restart_queue(BlockBackend *blk, bool is_write)
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{
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Coroutine *co;
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RestartData rd = {
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.blk = blk,
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.is_write = is_write
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};
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co = qemu_coroutine_create(throttle_group_restart_queue_entry, &rd);
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aio_co_enter(blk_get_aio_context(blk), co);
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}
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void throttle_group_restart_blk(BlockBackend *blk)
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{
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BlockBackendPublic *blkp = blk_get_public(blk);
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if (blkp->throttle_state) {
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throttle_group_restart_queue(blk, 0);
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throttle_group_restart_queue(blk, 1);
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}
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}
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/* Update the throttle configuration for a particular group. Similar
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* to throttle_config(), but guarantees atomicity within the
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* throttling group.
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*
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* @blk: a BlockBackend that is a member of the group
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* @cfg: the configuration to set
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*/
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void throttle_group_config(BlockBackend *blk, ThrottleConfig *cfg)
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{
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BlockBackendPublic *blkp = blk_get_public(blk);
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ThrottleState *ts = blkp->throttle_state;
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ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
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qemu_mutex_lock(&tg->lock);
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throttle_config(ts, tg->clock_type, cfg);
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qemu_mutex_unlock(&tg->lock);
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throttle_group_restart_blk(blk);
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}
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/* Get the throttle configuration from a particular group. Similar to
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* throttle_get_config(), but guarantees atomicity within the
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* throttling group.
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*
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* @blk: a BlockBackend that is a member of the group
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* @cfg: the configuration will be written here
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*/
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void throttle_group_get_config(BlockBackend *blk, ThrottleConfig *cfg)
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{
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BlockBackendPublic *blkp = blk_get_public(blk);
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ThrottleState *ts = blkp->throttle_state;
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ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
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qemu_mutex_lock(&tg->lock);
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throttle_get_config(ts, cfg);
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qemu_mutex_unlock(&tg->lock);
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}
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/* ThrottleTimers callback. This wakes up a request that was waiting
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* because it had been throttled.
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*
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* @blk: the BlockBackend whose request had been throttled
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* @is_write: the type of operation (read/write)
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*/
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static void timer_cb(BlockBackend *blk, bool is_write)
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{
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BlockBackendPublic *blkp = blk_get_public(blk);
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ThrottleState *ts = blkp->throttle_state;
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ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
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/* The timer has just been fired, so we can update the flag */
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qemu_mutex_lock(&tg->lock);
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tg->any_timer_armed[is_write] = false;
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qemu_mutex_unlock(&tg->lock);
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/* Run the request that was waiting for this timer */
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throttle_group_restart_queue(blk, is_write);
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}
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static void read_timer_cb(void *opaque)
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{
|
|
timer_cb(opaque, false);
|
|
}
|
|
|
|
static void write_timer_cb(void *opaque)
|
|
{
|
|
timer_cb(opaque, true);
|
|
}
|
|
|
|
/* Register a BlockBackend 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.
|
|
*
|
|
* @blk: the BlockBackend to insert
|
|
* @groupname: the name of the group
|
|
*/
|
|
void throttle_group_register_blk(BlockBackend *blk, const char *groupname)
|
|
{
|
|
int i;
|
|
BlockBackendPublic *blkp = blk_get_public(blk);
|
|
ThrottleState *ts = throttle_group_incref(groupname);
|
|
ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
|
|
blkp->throttle_state = ts;
|
|
|
|
qemu_mutex_lock(&tg->lock);
|
|
/* If the ThrottleGroup is new set this BlockBackend as the token */
|
|
for (i = 0; i < 2; i++) {
|
|
if (!tg->tokens[i]) {
|
|
tg->tokens[i] = blk;
|
|
}
|
|
}
|
|
|
|
QLIST_INSERT_HEAD(&tg->head, blkp, round_robin);
|
|
|
|
throttle_timers_init(&blkp->throttle_timers,
|
|
blk_get_aio_context(blk),
|
|
tg->clock_type,
|
|
read_timer_cb,
|
|
write_timer_cb,
|
|
blk);
|
|
|
|
qemu_mutex_unlock(&tg->lock);
|
|
}
|
|
|
|
/* Unregister a BlockBackend from its group, removing it from the list,
|
|
* destroying the timers and setting the throttle_state pointer to NULL.
|
|
*
|
|
* The BlockBackend 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.
|
|
*
|
|
* @blk: the BlockBackend to remove
|
|
*/
|
|
void throttle_group_unregister_blk(BlockBackend *blk)
|
|
{
|
|
BlockBackendPublic *blkp = blk_get_public(blk);
|
|
ThrottleGroup *tg = container_of(blkp->throttle_state, ThrottleGroup, ts);
|
|
int i;
|
|
|
|
assert(blkp->pending_reqs[0] == 0 && blkp->pending_reqs[1] == 0);
|
|
assert(qemu_co_queue_empty(&blkp->throttled_reqs[0]));
|
|
assert(qemu_co_queue_empty(&blkp->throttled_reqs[1]));
|
|
|
|
qemu_mutex_lock(&tg->lock);
|
|
for (i = 0; i < 2; i++) {
|
|
if (tg->tokens[i] == blk) {
|
|
BlockBackend *token = throttle_group_next_blk(blk);
|
|
/* Take care of the case where this is the last blk in the group */
|
|
if (token == blk) {
|
|
token = NULL;
|
|
}
|
|
tg->tokens[i] = token;
|
|
}
|
|
}
|
|
|
|
/* remove the current blk from the list */
|
|
QLIST_REMOVE(blkp, round_robin);
|
|
throttle_timers_destroy(&blkp->throttle_timers);
|
|
qemu_mutex_unlock(&tg->lock);
|
|
|
|
throttle_group_unref(&tg->ts);
|
|
blkp->throttle_state = NULL;
|
|
}
|
|
|
|
static void throttle_groups_init(void)
|
|
{
|
|
qemu_mutex_init(&throttle_groups_lock);
|
|
}
|
|
|
|
block_init(throttle_groups_init);
|