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Some more taskqueue optimizations.

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- Optimize enqueue for two task priority values by adding new tq_hint
field, pointing to the last task inserted into the middle of the list.
In case of more then two priority values it should halve average search.
 - Move tq_active insert/remove out of the taskqueue_run_locked loop.
Instead of dirtying few shared cache lines per task introduce different
mechanism to drain active tasks, based on task sequence number counter,
that uses only cache lines already present in cache.  Since the new
mechanism does not need ordering, switch tq_active from TAILQ to LIST.
 - Move static and dynamic struct taskqueue fields into different cache
lines.  Move lock into its own cache line, so that heavy lock spinning
by multiple waiting threads would not affect the running thread.
 - While there, correct some TQ_SLEEP() wait messages.

This change fixes certain ZFS write workloads, causing huge congestion
on taskqueue lock.  Those workloads combine some large block writes to
saturate the pool and trigger allocation throttling, which uses higher
priority tasks to requeue the delayed I/Os, with many small blocks to
generate deep queue of small tasks for taskqueue to sort.

MFC after:	1 week
Sponsored by:	iXsystems, Inc.
This commit is contained in:
Alexander Motin 2019-11-01 22:49:44 +00:00
parent 08b86a1a8a
commit 3db35ffa2a
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=354241
2 changed files with 90 additions and 116 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

89
sys/kern/subr_gtaskqueue.c
View File

@ -57,26 +57,26 @@ TASKQGROUP_DEFINE(softirq, mp_ncpus, 1);
TASKQGROUP_DEFINE(config, 1, 1);
struct gtaskqueue_busy {
struct gtask *tb_running;
TAILQ_ENTRY(gtaskqueue_busy) tb_link;
struct gtask *tb_running;
u_int tb_seq;
LIST_ENTRY(gtaskqueue_busy) tb_link;
};
static struct gtask * const TB_DRAIN_WAITER = (struct gtask *)0x1;
typedef void (*gtaskqueue_enqueue_fn)(void *context);
struct gtaskqueue {
STAILQ_HEAD(, gtask) tq_queue;
LIST_HEAD(, gtaskqueue_busy) tq_active;
u_int tq_seq;
int tq_callouts;
struct mtx_padalign tq_mutex;
gtaskqueue_enqueue_fn tq_enqueue;
void *tq_context;
char *tq_name;
TAILQ_HEAD(, gtaskqueue_busy) tq_active;
struct mtx tq_mutex;
struct thread **tq_threads;
int tq_tcount;
int tq_spin;
int tq_flags;
int tq_callouts;
taskqueue_callback_fn tq_callbacks[TASKQUEUE_NUM_CALLBACKS];
void *tq_cb_contexts[TASKQUEUE_NUM_CALLBACKS];
};
@ -115,12 +115,11 @@ gtask_dump(struct gtask *gtask)
#endif
static __inline int
TQ_SLEEP(struct gtaskqueue *tq, void *p, struct mtx *m, int pri, const char *wm,
int t)
TQ_SLEEP(struct gtaskqueue *tq, void *p, const char *wm)
{
if (tq->tq_spin)
return (msleep_spin(p, m, wm, t));
return (msleep(p, m, pri, wm, t));
return (msleep_spin(p, (struct mtx *)&tq->tq_mutex, wm, 0));
return (msleep(p, &tq->tq_mutex, 0, wm, 0));
}
static struct gtaskqueue *
@ -144,7 +143,7 @@ _gtaskqueue_create(const char *name, int mflags,
}
STAILQ_INIT(&queue->tq_queue);
TAILQ_INIT(&queue->tq_active);
LIST_INIT(&queue->tq_active);
queue->tq_enqueue = enqueue;
queue->tq_context = context;
queue->tq_name = tq_name;
@ -167,7 +166,7 @@ gtaskqueue_terminate(struct thread **pp, struct gtaskqueue *tq)
while (tq->tq_tcount > 0 || tq->tq_callouts > 0) {
wakeup(tq);
TQ_SLEEP(tq, pp, &tq->tq_mutex, PWAIT, "taskqueue_destroy", 0);
TQ_SLEEP(tq, pp, "gtq_destroy");
}
}
@ -178,7 +177,7 @@ gtaskqueue_free(struct gtaskqueue *queue)
TQ_LOCK(queue);
queue->tq_flags &= ~TQ_FLAGS_ACTIVE;
gtaskqueue_terminate(queue->tq_threads, queue);
KASSERT(TAILQ_EMPTY(&queue->tq_active), ("Tasks still running?"));
KASSERT(LIST_EMPTY(&queue->tq_active), ("Tasks still running?"));
KASSERT(queue->tq_callouts == 0, ("Armed timeout tasks"));
mtx_destroy(&queue->tq_mutex);
free(queue->tq_threads, M_GTASKQUEUE);
@ -285,7 +284,7 @@ gtaskqueue_drain_tq_queue(struct gtaskqueue *queue)
* have completed or are currently executing.
*/
while (t_barrier.ta_flags & TASK_ENQUEUED)
TQ_SLEEP(queue, &t_barrier, &queue->tq_mutex, PWAIT, "-", 0);
TQ_SLEEP(queue, &t_barrier, "gtq_qdrain");
}
/*
@ -296,31 +295,24 @@ gtaskqueue_drain_tq_queue(struct gtaskqueue *queue)
static void
gtaskqueue_drain_tq_active(struct gtaskqueue *queue)
{
struct gtaskqueue_busy tb_marker, *tb_first;
struct gtaskqueue_busy *tb;
u_int seq;
if (TAILQ_EMPTY(&queue->tq_active))
if (LIST_EMPTY(&queue->tq_active))
return;
/* Block taskq_terminate().*/
queue->tq_callouts++;
/*
* Wait for all currently executing taskqueue threads
* to go idle.
*/
tb_marker.tb_running = TB_DRAIN_WAITER;
TAILQ_INSERT_TAIL(&queue->tq_active, &tb_marker, tb_link);
while (TAILQ_FIRST(&queue->tq_active) != &tb_marker)
TQ_SLEEP(queue, &tb_marker, &queue->tq_mutex, PWAIT, "-", 0);
TAILQ_REMOVE(&queue->tq_active, &tb_marker, tb_link);
/*
* Wakeup any other drain waiter that happened to queue up
* without any intervening active thread.
*/
tb_first = TAILQ_FIRST(&queue->tq_active);
if (tb_first != NULL && tb_first->tb_running == TB_DRAIN_WAITER)
wakeup(tb_first);
/* Wait for any active task with sequence from the past. */
seq = queue->tq_seq;
restart:
LIST_FOREACH(tb, &queue->tq_active, tb_link) {
if ((int)(tb->tb_seq - seq) <= 0) {
TQ_SLEEP(queue, tb->tb_running, "gtq_adrain");
goto restart;
}
}
/* Release taskqueue_terminate(). */
queue->tq_callouts--;
@ -352,40 +344,27 @@ static void
gtaskqueue_run_locked(struct gtaskqueue *queue)
{
struct gtaskqueue_busy tb;
struct gtaskqueue_busy *tb_first;
struct gtask *gtask;
KASSERT(queue != NULL, ("tq is NULL"));
TQ_ASSERT_LOCKED(queue);
tb.tb_running = NULL;
LIST_INSERT_HEAD(&queue->tq_active, &tb, tb_link);
while (STAILQ_FIRST(&queue->tq_queue)) {
TAILQ_INSERT_TAIL(&queue->tq_active, &tb, tb_link);
/*
* Carefully remove the first task from the queue and
* clear its TASK_ENQUEUED flag
*/
gtask = STAILQ_FIRST(&queue->tq_queue);
KASSERT(gtask != NULL, ("task is NULL"));
while ((gtask = STAILQ_FIRST(&queue->tq_queue)) != NULL) {
STAILQ_REMOVE_HEAD(&queue->tq_queue, ta_link);
gtask->ta_flags &= ~TASK_ENQUEUED;
tb.tb_running = gtask;
tb.tb_seq = ++queue->tq_seq;
TQ_UNLOCK(queue);
KASSERT(gtask->ta_func != NULL, ("task->ta_func is NULL"));
gtask->ta_func(gtask->ta_context);
TQ_LOCK(queue);
tb.tb_running = NULL;
wakeup(gtask);
TAILQ_REMOVE(&queue->tq_active, &tb, tb_link);
tb_first = TAILQ_FIRST(&queue->tq_active);
if (tb_first != NULL &&
tb_first->tb_running == TB_DRAIN_WAITER)
wakeup(tb_first);
}
LIST_REMOVE(&tb, tb_link);
}
static int
@ -394,7 +373,7 @@ task_is_running(struct gtaskqueue *queue, struct gtask *gtask)
struct gtaskqueue_busy *tb;
TQ_ASSERT_LOCKED(queue);
TAILQ_FOREACH(tb, &queue->tq_active, tb_link) {
LIST_FOREACH(tb, &queue->tq_active, tb_link) {
if (tb->tb_running == gtask)
return (1);
}
@ -427,7 +406,7 @@ static void
gtaskqueue_drain_locked(struct gtaskqueue *queue, struct gtask *gtask)
{
while ((gtask->ta_flags & TASK_ENQUEUED) || task_is_running(queue, gtask))
TQ_SLEEP(queue, gtask, &queue->tq_mutex, PWAIT, "-", 0);
TQ_SLEEP(queue, gtask, "gtq_drain");
}
void
@ -563,7 +542,7 @@ gtaskqueue_thread_loop(void *arg)
*/
if ((tq->tq_flags & TQ_FLAGS_ACTIVE) == 0)
break;
TQ_SLEEP(tq, tq, &tq->tq_mutex, 0, "-", 0);
TQ_SLEEP(tq, tq, "-");
}
gtaskqueue_run_locked(tq);
/*
@ -589,7 +568,7 @@ gtaskqueue_thread_enqueue(void *context)
tqp = context;
tq = *tqp;
wakeup_one(tq);
wakeup_any(tq);
}

117
sys/kern/subr_taskqueue.c
View File

@ -56,24 +56,25 @@ static void taskqueue_swi_enqueue(void *);
static void taskqueue_swi_giant_enqueue(void *);
struct taskqueue_busy {
struct task *tb_running;
TAILQ_ENTRY(taskqueue_busy) tb_link;
struct task *tb_running;
u_int tb_seq;
LIST_ENTRY(taskqueue_busy) tb_link;
};
struct task * const TB_DRAIN_WAITER = (struct task *)0x1;
struct taskqueue {
STAILQ_HEAD(, task) tq_queue;
LIST_HEAD(, taskqueue_busy) tq_active;
struct task *tq_hint;
u_int tq_seq;
int tq_callouts;
struct mtx_padalign tq_mutex;
taskqueue_enqueue_fn tq_enqueue;
void *tq_context;
char *tq_name;
TAILQ_HEAD(, taskqueue_busy) tq_active;
struct mtx tq_mutex;
struct thread **tq_threads;
int tq_tcount;
int tq_spin;
int tq_flags;
int tq_callouts;
taskqueue_callback_fn tq_callbacks[TASKQUEUE_NUM_CALLBACKS];
void *tq_cb_contexts[TASKQUEUE_NUM_CALLBACKS];
};
@ -116,12 +117,11 @@ _timeout_task_init(struct taskqueue *queue, struct timeout_task *timeout_task,
}
static __inline int
TQ_SLEEP(struct taskqueue *tq, void *p, struct mtx *m, int pri, const char *wm,
int t)
TQ_SLEEP(struct taskqueue *tq, void *p, const char *wm)
{
if (tq->tq_spin)
return (msleep_spin(p, m, wm, t));
return (msleep(p, m, pri, wm, t));
return (msleep_spin(p, (struct mtx *)&tq->tq_mutex, wm, 0));
return (msleep(p, &tq->tq_mutex, 0, wm, 0));
}
static struct taskqueue *
@ -145,7 +145,7 @@ _taskqueue_create(const char *name, int mflags,
snprintf(tq_name, TASKQUEUE_NAMELEN, "%s", (name) ? name : "taskqueue");
STAILQ_INIT(&queue->tq_queue);
TAILQ_INIT(&queue->tq_active);
LIST_INIT(&queue->tq_active);
queue->tq_enqueue = enqueue;
queue->tq_context = context;
queue->tq_name = tq_name;
@ -196,7 +196,7 @@ taskqueue_terminate(struct thread **pp, struct taskqueue *tq)
while (tq->tq_tcount > 0 || tq->tq_callouts > 0) {
wakeup(tq);
TQ_SLEEP(tq, pp, &tq->tq_mutex, PWAIT, "taskqueue_destroy", 0);
TQ_SLEEP(tq, pp, "tq_destroy");
}
}
@ -207,7 +207,7 @@ taskqueue_free(struct taskqueue *queue)
TQ_LOCK(queue);
queue->tq_flags &= ~TQ_FLAGS_ACTIVE;
taskqueue_terminate(queue->tq_threads, queue);
KASSERT(TAILQ_EMPTY(&queue->tq_active), ("Tasks still running?"));
KASSERT(LIST_EMPTY(&queue->tq_active), ("Tasks still running?"));
KASSERT(queue->tq_callouts == 0, ("Armed timeout tasks"));
mtx_destroy(&queue->tq_mutex);
free(queue->tq_threads, M_TASKQUEUE);
@ -233,21 +233,30 @@ taskqueue_enqueue_locked(struct taskqueue *queue, struct task *task)
}
/*
* Optimise the case when all tasks have the same priority.
* Optimise cases when all tasks use small set of priorities.
* In case of only one priority we always insert at the end.
* In case of two tq_hint typically gives the insertion point.
* In case of more then two tq_hint should halve the search.
*/
prev = STAILQ_LAST(&queue->tq_queue, task, ta_link);
if (!prev || prev->ta_priority >= task->ta_priority) {
STAILQ_INSERT_TAIL(&queue->tq_queue, task, ta_link);
} else {
prev = NULL;
for (ins = STAILQ_FIRST(&queue->tq_queue); ins;
prev = ins, ins = STAILQ_NEXT(ins, ta_link))
prev = queue->tq_hint;
if (prev && prev->ta_priority >= task->ta_priority) {
ins = STAILQ_NEXT(prev, ta_link);
} else {
prev = NULL;
ins = STAILQ_FIRST(&queue->tq_queue);
}
for (; ins; prev = ins, ins = STAILQ_NEXT(ins, ta_link))
if (ins->ta_priority < task->ta_priority)
break;
if (prev)
if (prev) {
STAILQ_INSERT_AFTER(&queue->tq_queue, prev, task, ta_link);
else
queue->tq_hint = task;
} else
STAILQ_INSERT_HEAD(&queue->tq_queue, task, ta_link);
}
@ -364,6 +373,7 @@ taskqueue_drain_tq_queue(struct taskqueue *queue)
*/
TASK_INIT(&t_barrier, USHRT_MAX, taskqueue_task_nop_fn, &t_barrier);
STAILQ_INSERT_TAIL(&queue->tq_queue, &t_barrier, ta_link);
queue->tq_hint = &t_barrier;
t_barrier.ta_pending = 1;
/*
@ -371,7 +381,7 @@ taskqueue_drain_tq_queue(struct taskqueue *queue)
* have completed or are currently executing.
*/
while (t_barrier.ta_pending != 0)
TQ_SLEEP(queue, &t_barrier, &queue->tq_mutex, PWAIT, "-", 0);
TQ_SLEEP(queue, &t_barrier, "tq_qdrain");
return (1);
}
@ -383,31 +393,24 @@ taskqueue_drain_tq_queue(struct taskqueue *queue)
static int
taskqueue_drain_tq_active(struct taskqueue *queue)
{
struct taskqueue_busy tb_marker, *tb_first;
struct taskqueue_busy *tb;
u_int seq;
if (TAILQ_EMPTY(&queue->tq_active))
if (LIST_EMPTY(&queue->tq_active))
return (0);
/* Block taskq_terminate().*/
queue->tq_callouts++;
/*
* Wait for all currently executing taskqueue threads
* to go idle.
*/
tb_marker.tb_running = TB_DRAIN_WAITER;
TAILQ_INSERT_TAIL(&queue->tq_active, &tb_marker, tb_link);
while (TAILQ_FIRST(&queue->tq_active) != &tb_marker)
TQ_SLEEP(queue, &tb_marker, &queue->tq_mutex, PWAIT, "-", 0);
TAILQ_REMOVE(&queue->tq_active, &tb_marker, tb_link);
/*
* Wakeup any other drain waiter that happened to queue up
* without any intervening active thread.
*/
tb_first = TAILQ_FIRST(&queue->tq_active);
if (tb_first != NULL && tb_first->tb_running == TB_DRAIN_WAITER)
wakeup(tb_first);
/* Wait for any active task with sequence from the past. */
seq = queue->tq_seq;
restart:
LIST_FOREACH(tb, &queue->tq_active, tb_link) {
if ((int)(tb->tb_seq - seq) <= 0) {
TQ_SLEEP(queue, tb->tb_running, "tq_adrain");
goto restart;
}
}
/* Release taskqueue_terminate(). */
queue->tq_callouts--;
@ -440,42 +443,31 @@ static void
taskqueue_run_locked(struct taskqueue *queue)
{
struct taskqueue_busy tb;
struct taskqueue_busy *tb_first;
struct task *task;
int pending;
KASSERT(queue != NULL, ("tq is NULL"));
TQ_ASSERT_LOCKED(queue);
tb.tb_running = NULL;
LIST_INSERT_HEAD(&queue->tq_active, &tb, tb_link);
while (STAILQ_FIRST(&queue->tq_queue)) {
TAILQ_INSERT_TAIL(&queue->tq_active, &tb, tb_link);
/*
* Carefully remove the first task from the queue and
* zero its pending count.
*/
task = STAILQ_FIRST(&queue->tq_queue);
KASSERT(task != NULL, ("task is NULL"));
while ((task = STAILQ_FIRST(&queue->tq_queue)) != NULL) {
STAILQ_REMOVE_HEAD(&queue->tq_queue, ta_link);
if (queue->tq_hint == task)
queue->tq_hint = NULL;
pending = task->ta_pending;
task->ta_pending = 0;
tb.tb_running = task;
tb.tb_seq = ++queue->tq_seq;
TQ_UNLOCK(queue);
KASSERT(task->ta_func != NULL, ("task->ta_func is NULL"));
task->ta_func(task->ta_context, pending);
TQ_LOCK(queue);
tb.tb_running = NULL;
wakeup(task);
TAILQ_REMOVE(&queue->tq_active, &tb, tb_link);
tb_first = TAILQ_FIRST(&queue->tq_active);
if (tb_first != NULL &&
tb_first->tb_running == TB_DRAIN_WAITER)
wakeup(tb_first);
}
LIST_REMOVE(&tb, tb_link);
}
void
@ -493,7 +485,7 @@ task_is_running(struct taskqueue *queue, struct task *task)
struct taskqueue_busy *tb;
TQ_ASSERT_LOCKED(queue);
TAILQ_FOREACH(tb, &queue->tq_active, tb_link) {
LIST_FOREACH(tb, &queue->tq_active, tb_link) {
if (tb->tb_running == task)
return (1);
}
@ -522,8 +514,11 @@ taskqueue_cancel_locked(struct taskqueue *queue, struct task *task,
u_int *pendp)
{
if (task->ta_pending > 0)
if (task->ta_pending > 0) {
STAILQ_REMOVE(&queue->tq_queue, task, task, ta_link);
if (queue->tq_hint == task)
queue->tq_hint = NULL;
}
if (pendp != NULL)
*pendp = task->ta_pending;
task->ta_pending = 0;
@ -572,7 +567,7 @@ taskqueue_drain(struct taskqueue *queue, struct task *task)
TQ_LOCK(queue);
while (task->ta_pending != 0 || task_is_running(queue, task))
TQ_SLEEP(queue, task, &queue->tq_mutex, PWAIT, "-", 0);
TQ_SLEEP(queue, task, "tq_drain");
TQ_UNLOCK(queue);
}
@ -791,7 +786,7 @@ taskqueue_thread_loop(void *arg)
*/
if ((tq->tq_flags & TQ_FLAGS_ACTIVE) == 0)
break;
TQ_SLEEP(tq, tq, &tq->tq_mutex, 0, "-", 0);
TQ_SLEEP(tq, tq, "-");
}
taskqueue_run_locked(tq);
/*