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Linux: Cleanup taskq threads spawn/exit 

This changes taskq_thread_should_stop() to limit maximum exit rate
for idle threads to one per 5 seconds.  I believe the previous one
was broken, not allowing any thread exits for tasks arriving more
than one at a time and so completing while others are running.

Also while there:
 - Remove taskq_thread_spawn() calls on task allocation errors.
 - Remove extra taskq_thread_should_stop() call.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Rich Ercolani <rincebrain@gmail.com>
Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
Sponsored by:	iXsystems, Inc.
Closes #15873
This commit is contained in:
Alexander Motin 2024-02-13 14:15:16 -05:00 committed by Brian Behlendorf
parent fdd97e0093
commit 793a2cff2a
3 changed files with 34 additions and 71 deletions
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2
include/os/linux/spl/sys/taskq.h
View File

@ -104,7 +104,7 @@ typedef struct taskq {
/* list node for the cpu hotplug callback */
struct hlist_node tq_hp_cb_node;
boolean_t tq_hp_support;
unsigned long lastshouldstop; /* when to purge dynamic */
unsigned long lastspawnstop; /* when to purge dynamic */
} taskq_t;
typedef struct taskq_ent {

18
man/man4/spl.4
View File

@ -186,18 +186,8 @@ reading it could cause a lock-up if the list grow too large
without limiting the output.
"(truncated)" will be shown if the list is larger than the limit.
.
.It Sy spl_taskq_thread_timeout_ms Ns = Ns Sy 10000 Pq uint
(Linux-only)
How long a taskq has to have had no work before we tear it down.
Previously, we would tear down a dynamic taskq worker as soon
as we noticed it had no work, but it was observed that this led
to a lot of churn in tearing down things we then immediately
spawned anew.
In practice, it seems any nonzero value will remove the vast
majority of this churn, while the nontrivially larger value
was chosen to help filter out the little remaining churn on
a mostly idle system.
Setting this value to
.Sy 0
will revert to the previous behavior.
.It Sy spl_taskq_thread_timeout_ms Ns = Ns Sy 5000 Pq uint
Minimum idle threads exit interval for dynamic taskqs.
Smaller values allow idle threads exit more often and potentially be
respawned again on demand, causing more churn.
.El

81
module/os/linux/spl/spl-taskq.c
View File

@ -36,12 +36,12 @@ static int spl_taskq_thread_bind = 0;
module_param(spl_taskq_thread_bind, int, 0644);
MODULE_PARM_DESC(spl_taskq_thread_bind, "Bind taskq thread to CPU by default");
static uint_t spl_taskq_thread_timeout_ms = 10000;
static uint_t spl_taskq_thread_timeout_ms = 5000;
/* BEGIN CSTYLED */
module_param(spl_taskq_thread_timeout_ms, uint, 0644);
/* END CSTYLED */
MODULE_PARM_DESC(spl_taskq_thread_timeout_ms,
"Time to require a dynamic thread be idle before it gets cleaned up");
"Minimum idle threads exit interval for dynamic taskqs");
static int spl_taskq_thread_dynamic = 1;
module_param(spl_taskq_thread_dynamic, int, 0444);
@ -594,8 +594,7 @@ taskq_dispatch(taskq_t *tq, task_func_t func, void *arg, uint_t flags)
ASSERT(tq->tq_nactive <= tq->tq_nthreads);
if ((flags & TQ_NOQUEUE) && (tq->tq_nactive == tq->tq_nthreads)) {
/* Dynamic taskq may be able to spawn another thread */
if (!(tq->tq_flags & TASKQ_DYNAMIC) ||
taskq_thread_spawn(tq) == 0)
if (taskq_thread_spawn(tq) == 0)
goto out;
}
@ -629,11 +628,11 @@ taskq_dispatch(taskq_t *tq, task_func_t func, void *arg, uint_t flags)
spin_unlock(&t->tqent_lock);
wake_up(&tq->tq_work_waitq);
out:
/* Spawn additional taskq threads if required. */
if (!(flags & TQ_NOQUEUE) && tq->tq_nactive == tq->tq_nthreads)
(void) taskq_thread_spawn(tq);
out:
spin_unlock_irqrestore(&tq->tq_lock, irqflags);
return (rc);
}
@ -676,10 +675,11 @@ taskq_dispatch_delay(taskq_t *tq, task_func_t func, void *arg,
ASSERT(!(t->tqent_flags & TQENT_FLAG_PREALLOC));
spin_unlock(&t->tqent_lock);
out:
/* Spawn additional taskq threads if required. */
if (tq->tq_nactive == tq->tq_nthreads)
(void) taskq_thread_spawn(tq);
out:
spin_unlock_irqrestore(&tq->tq_lock, irqflags);
return (rc);
}
@ -704,9 +704,8 @@ taskq_dispatch_ent(taskq_t *tq, task_func_t func, void *arg, uint_t flags,
if ((flags & TQ_NOQUEUE) && (tq->tq_nactive == tq->tq_nthreads)) {
/* Dynamic taskq may be able to spawn another thread */
if (!(tq->tq_flags & TASKQ_DYNAMIC) ||
taskq_thread_spawn(tq) == 0)
goto out2;
if (taskq_thread_spawn(tq) == 0)
goto out;
flags |= TQ_FRONT;
}
@ -742,11 +741,11 @@ taskq_dispatch_ent(taskq_t *tq, task_func_t func, void *arg, uint_t flags,
spin_unlock(&t->tqent_lock);
wake_up(&tq->tq_work_waitq);
out:
/* Spawn additional taskq threads if required. */
if (tq->tq_nactive == tq->tq_nthreads)
(void) taskq_thread_spawn(tq);
out2:
out:
spin_unlock_irqrestore(&tq->tq_lock, irqflags);
}
EXPORT_SYMBOL(taskq_dispatch_ent);
@ -825,6 +824,7 @@ taskq_thread_spawn(taskq_t *tq)
if (!(tq->tq_flags & TASKQ_DYNAMIC))
return (0);
tq->lastspawnstop = jiffies;
if ((tq->tq_nthreads + tq->tq_nspawn < tq->tq_maxthreads) &&
(tq->tq_flags & TASKQ_ACTIVE)) {
spawning = (++tq->tq_nspawn);
@ -836,9 +836,9 @@ taskq_thread_spawn(taskq_t *tq)
}
/*
* Threads in a dynamic taskq should only exit once it has been completely
* drained and no other threads are actively servicing tasks. This prevents
* threads from being created and destroyed more than is required.
* Threads in a dynamic taskq may exit once there is no more work to do.
* To prevent threads from being created and destroyed too often limit
* the exit rate to one per spl_taskq_thread_timeout_ms.
*
* The first thread is the thread list is treated as the primary thread.
* There is nothing special about the primary thread but in order to avoid
@ -847,44 +847,22 @@ taskq_thread_spawn(taskq_t *tq)
static int
taskq_thread_should_stop(taskq_t *tq, taskq_thread_t *tqt)
{
if (!(tq->tq_flags & TASKQ_DYNAMIC))
ASSERT(!taskq_next_ent(tq));
if (!(tq->tq_flags & TASKQ_DYNAMIC) || !spl_taskq_thread_dynamic)
return (0);
if (!(tq->tq_flags & TASKQ_ACTIVE))
return (1);
if (list_first_entry(&(tq->tq_thread_list), taskq_thread_t,
tqt_thread_list) == tqt)
return (0);
int no_work =
((tq->tq_nspawn == 0) && /* No threads are being spawned */
(tq->tq_nactive == 0) && /* No threads are handling tasks */
(tq->tq_nthreads > 1) && /* More than 1 thread is running */
(!taskq_next_ent(tq)) && /* There are no pending tasks */
(spl_taskq_thread_dynamic)); /* Dynamic taskqs are allowed */
/*
* If we would have said stop before, let's instead wait a bit, maybe
* we'll see more work come our way soon...
*/
if (no_work) {
/* if it's 0, we want the old behavior. */
/* if the taskq is being torn down, we also want to go away. */
if (spl_taskq_thread_timeout_ms == 0 ||
!(tq->tq_flags & TASKQ_ACTIVE))
return (1);
unsigned long lasttime = tq->lastshouldstop;
if (lasttime > 0) {
if (time_after(jiffies, lasttime +
ASSERT3U(tq->tq_nthreads, >, 1);
if (tq->tq_nspawn != 0)
return (0);
if (time_before(jiffies, tq->lastspawnstop +
msecs_to_jiffies(spl_taskq_thread_timeout_ms)))
return (0);
tq->lastspawnstop = jiffies;
return (1);
else
return (0);
} else {
tq->lastshouldstop = jiffies;
}
} else {
tq->lastshouldstop = 0;
}
return (0);
}
static int
@ -935,10 +913,8 @@ taskq_thread(void *args)
if (list_empty(&tq->tq_pend_list) &&
list_empty(&tq->tq_prio_list)) {
if (taskq_thread_should_stop(tq, tqt)) {
wake_up_all(&tq->tq_wait_waitq);
if (taskq_thread_should_stop(tq, tqt))
break;
}
add_wait_queue_exclusive(&tq->tq_work_waitq, &wait);
spin_unlock_irqrestore(&tq->tq_lock, flags);
@ -1013,9 +989,6 @@ taskq_thread(void *args)
tqt->tqt_id = TASKQID_INVALID;
tqt->tqt_flags = 0;
wake_up_all(&tq->tq_wait_waitq);
} else {
if (taskq_thread_should_stop(tq, tqt))
break;
}
set_current_state(TASK_INTERRUPTIBLE);
@ -1122,7 +1095,7 @@ taskq_create(const char *name, int threads_arg, pri_t pri,
tq->tq_flags = (flags | TASKQ_ACTIVE);
tq->tq_next_id = TASKQID_INITIAL;
tq->tq_lowest_id = TASKQID_INITIAL;
tq->lastshouldstop = 0;
tq->lastspawnstop = jiffies;
INIT_LIST_HEAD(&tq->tq_free_list);
INIT_LIST_HEAD(&tq->tq_pend_list);
INIT_LIST_HEAD(&tq->tq_prio_list);