From: "tip-bot2 for Rik van Riel" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Rik van Riel <riel@surriel.com>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Mel Gorman <mgorman@suse.de>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [tip: sched/core] sched,fair: Skip newidle_balance if a wakeup is pending
Date: Wed, 12 May 2021 10:28:32 -0000 [thread overview]
Message-ID: <162081531253.29796.98482466243425223.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20210422130236.0bb353df@imladris.surriel.com>
The following commit has been merged into the sched/core branch of tip:
Commit-ID: e5e678e4fea26d73444f4427cbbaeab4fa79ecee
Gitweb: https://git.kernel.org/tip/e5e678e4fea26d73444f4427cbbaeab4fa79ecee
Author: Rik van Riel <riel@surriel.com>
AuthorDate: Thu, 22 Apr 2021 13:02:36 -04:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 12 May 2021 11:43:23 +02:00
sched,fair: Skip newidle_balance if a wakeup is pending
The try_to_wake_up function has an optimization where it can queue
a task for wakeup on its previous CPU, if the task is still in the
middle of going to sleep inside schedule().
Once schedule() re-enables IRQs, the task will be woken up with an
IPI, and placed back on the runqueue.
If we have such a wakeup pending, there is no need to search other
CPUs for runnable tasks. Just skip (or bail out early from) newidle
balancing, and run the just woken up task.
For a memcache like workload test, this reduces total CPU use by
about 2%, proportionally split between user and system time,
and p99 and p95 application response time by 10% on average.
The schedstats run_delay number shows a similar improvement.
Signed-off-by: Rik van Riel <riel@surriel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Acked-by: Mel Gorman <mgorman@suse.de>
Link: https://lkml.kernel.org/r/20210422130236.0bb353df@imladris.surriel.com
---
kernel/sched/fair.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 3248e24..d10c6cc 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10592,6 +10592,14 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
u64 curr_cost = 0;
update_misfit_status(NULL, this_rq);
+
+ /*
+ * There is a task waiting to run. No need to search for one.
+ * Return 0; the task will be enqueued when switching to idle.
+ */
+ if (this_rq->ttwu_pending)
+ return 0;
+
/*
* We must set idle_stamp _before_ calling idle_balance(), such that we
* measure the duration of idle_balance() as idle time.
@@ -10657,7 +10665,8 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
* Stop searching for tasks to pull if there are
* now runnable tasks on this rq.
*/
- if (pulled_task || this_rq->nr_running > 0)
+ if (pulled_task || this_rq->nr_running > 0 ||
+ this_rq->ttwu_pending)
break;
}
rcu_read_unlock();
next prev parent reply other threads:[~2021-05-12 10:30 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-22 17:02 [PATCH v4] sched,fair: Skip newidle_balance if a wakeup is pending Rik van Riel
2021-04-22 17:09 ` Vincent Guittot
2021-05-04 9:21 ` Peter Zijlstra
2021-04-24 9:30 ` Mel Gorman
2021-05-12 10:28 ` tip-bot2 for Rik van Riel [this message]
-- strict thread matches above, loose matches on Subject: below --
2021-04-20 16:07 [PATCH v3] sched,fair: skip " Rik van Riel
2021-04-22 7:36 ` [tip: sched/core] " tip-bot2 for Rik van Riel
2021-04-22 8:15 ` Peter Zijlstra
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