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Message-ID: <Y2ofXw0FfQHEBUpu@hirez.programming.kicks-ass.net>
Date: Tue, 8 Nov 2022 10:20:31 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Chengming Zhou <zhouchengming@...edance.com>
Cc: mingo@...hat.com, juri.lelli@...hat.com,
vincent.guittot@...aro.org, dietmar.eggemann@....com,
rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
bristot@...hat.com, vschneid@...hat.com,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/core: Minor optimize ttwu_runnable()
On Wed, Nov 02, 2022 at 06:23:43PM +0800, Chengming Zhou wrote:
> ttwu_runnable() is used as a fast wakeup path when the wakee task
> is between set_current_state() and schedule(), in which case all
> we need to do is change p->state back to TASK_RUNNING. So we don't
> need to update_rq_clock() and check_preempt_curr() in this case.
>
> Some performance numbers using mmtests/perfpipe on Intel Xeon server:
>
> linux-next patched
> Min Time 8.67 ( 0.00%) 8.66 ( 0.13%)
> 1st-qrtle Time 8.83 ( 0.00%) 8.72 ( 1.19%)
> 2nd-qrtle Time 8.90 ( 0.00%) 8.76 ( 1.57%)
> 3rd-qrtle Time 8.98 ( 0.00%) 8.82 ( 1.82%)
> Max-1 Time 8.67 ( 0.00%) 8.66 ( 0.13%)
> Max-5 Time 8.67 ( 0.00%) 8.66 ( 0.13%)
> Max-10 Time 8.79 ( 0.00%) 8.69 ( 1.09%)
> Max-90 Time 9.01 ( 0.00%) 8.84 ( 1.94%)
> Max-95 Time 9.02 ( 0.00%) 8.85 ( 1.86%)
> Max-99 Time 9.02 ( 0.00%) 8.88 ( 1.56%)
> Max Time 9.59 ( 0.00%) 8.89 ( 7.29%)
> Amean Time 8.92 ( 0.00%) 8.77 * 1.65%*
>
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
> ---
> kernel/sched/core.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 87c9cdf37a26..3785418de127 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3718,9 +3718,8 @@ static int ttwu_runnable(struct task_struct *p, int wake_flags)
>
> rq = __task_rq_lock(p, &rf);
> if (task_on_rq_queued(p)) {
> - /* check_preempt_curr() may use rq clock */
> - update_rq_clock(rq);
> - ttwu_do_wakeup(rq, p, wake_flags, &rf);
> + WRITE_ONCE(p->__state, TASK_RUNNING);
> + trace_sched_wakeup(p);
> ret = 1;
> }
> __task_rq_unlock(rq, &rf);
Yes, I think this is correct; however I would re-organize code a little.
How's this?
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index cb2aa2b54c7a..43d9a1551a5d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3602,15 +3602,40 @@ ttwu_stat(struct task_struct *p, int cpu, int wake_flags)
__schedstat_inc(p->stats.nr_wakeups_sync);
}
/*
- * Mark the task runnable and perform wakeup-preemption.
+ * Mark the task runnable...
*/
-static void ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags,
- struct rq_flags *rf)
+static inline void ttwu_do_wakeup(struct task_struct *p)
{
- check_preempt_curr(rq, p, wake_flags);
WRITE_ONCE(p->__state, TASK_RUNNING);
trace_sched_wakeup(p);
+}
+
+static void
+ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags,
+ struct rq_flags *rf)
+{
+ int en_flags = ENQUEUE_WAKEUP | ENQUEUE_NOCLOCK;
+
+ lockdep_assert_rq_held(rq);
+
+ if (p->sched_contributes_to_load)
+ rq->nr_uninterruptible--;
+
+#ifdef CONFIG_SMP
+ if (wake_flags & WF_MIGRATED)
+ en_flags |= ENQUEUE_MIGRATED;
+ else
+#endif
+ if (p->in_iowait) {
+ delayacct_blkio_end(p);
+ atomic_dec(&task_rq(p)->nr_iowait);
+ }
+
+ activate_task(rq, p, en_flags);
+ check_preempt_curr(rq, p, wake_flags);
+
+ ttwu_do_wakeup(p);
#ifdef CONFIG_SMP
if (p->sched_class->task_woken) {
@@ -3640,31 +3666,6 @@ static void ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags,
#endif
}
-static void
-ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags,
- struct rq_flags *rf)
-{
- int en_flags = ENQUEUE_WAKEUP | ENQUEUE_NOCLOCK;
-
- lockdep_assert_rq_held(rq);
-
- if (p->sched_contributes_to_load)
- rq->nr_uninterruptible--;
-
-#ifdef CONFIG_SMP
- if (wake_flags & WF_MIGRATED)
- en_flags |= ENQUEUE_MIGRATED;
- else
-#endif
- if (p->in_iowait) {
- delayacct_blkio_end(p);
- atomic_dec(&task_rq(p)->nr_iowait);
- }
-
- activate_task(rq, p, en_flags);
- ttwu_do_wakeup(rq, p, wake_flags, rf);
-}
-
/*
* Consider @p being inside a wait loop:
*
@@ -3698,9 +3699,7 @@ static int ttwu_runnable(struct task_struct *p, int wake_flags)
rq = __task_rq_lock(p, &rf);
if (task_on_rq_queued(p)) {
- /* check_preempt_curr() may use rq clock */
- update_rq_clock(rq);
- ttwu_do_wakeup(rq, p, wake_flags, &rf);
+ ttwu_do_wakeup(p);
ret = 1;
}
__task_rq_unlock(rq, &rf);
@@ -4062,8 +4061,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
goto out;
trace_sched_waking(p);
- WRITE_ONCE(p->__state, TASK_RUNNING);
- trace_sched_wakeup(p);
+ ttwu_do_wakeup(p);
goto out;
}
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