--- /dev/null
+/*
+ * 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
+ * mostly transparent to outside users (but see the documentation in
+ * throttle_groups_lock()).
+ *
+ * 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 ThrottleGroup
+ */
+static ThrottleGroup *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;
+}
+
+/* Decrease the reference count of a ThrottleGroup.
+ *
+ * When the reference count reaches zero the ThrottleGroup is
+ * destroyed.
+ *
+ * @tg: The ThrottleGroup to unref
+ */
+static void throttle_group_unref(ThrottleGroup *tg)
+{
+ 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;
+ ThrottleGroup *tg = throttle_group_incref(groupname);
+ int clock_type = QEMU_CLOCK_REALTIME;
+
+ if (qtest_enabled()) {
+ /* For testing block IO throttling only */
+ clock_type = QEMU_CLOCK_VIRTUAL;
+ }
+
+ bs->throttle_state = &tg->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 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;
+
+ 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);
+ bs->throttle_state = NULL;
+}
+
+/* Acquire the lock of this throttling group.
+ *
+ * You won't normally need to use this. None of the functions from the
+ * ThrottleGroup API require you to acquire the lock since all of them
+ * deal with it internally.
+ *
+ * This should only be used in exceptional cases when you want to
+ * access the protected fields of a BlockDriverState directly
+ * (e.g. bdrv_swap()).
+ *
+ * @bs: a BlockDriverState that is member of the group
+ */
+void throttle_group_lock(BlockDriverState *bs)
+{
+ ThrottleGroup *tg = container_of(bs->throttle_state, ThrottleGroup, ts);
+ qemu_mutex_lock(&tg->lock);
+}
+
+/* Release the lock of this throttling group.
+ *
+ * See the comments in throttle_group_lock().
+ */
+void throttle_group_unlock(BlockDriverState *bs)
+{
+ ThrottleGroup *tg = container_of(bs->throttle_state, ThrottleGroup, ts);
+ qemu_mutex_unlock(&tg->lock);
+}
+
+static void throttle_groups_init(void)
+{
+ qemu_mutex_init(&throttle_groups_lock);
+}
+
+block_init(throttle_groups_init);
Code Review / kvmfornfv.git / blobdiff