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>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [tip: sched/core] sched,fair: skip newidle_balance if a wakeup is pending
Date: Thu, 22 Apr 2021 07:36:00 -0000 [thread overview]
Message-ID: <161907696062.29796.108437696048031441.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20210420120705.5c705d4b@imladris.surriel.com>
The following commit has been merged into the sched/core branch of tip:
Commit-ID: 9c9f520a14670ad59da2f700660f7601ec9e0b07
Gitweb: https://git.kernel.org/tip/9c9f520a14670ad59da2f700660f7601ec9e0b07
Author: Rik van Riel <riel@surriel.com>
AuthorDate: Tue, 20 Apr 2021 12:07:05 -04:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 21 Apr 2021 13:55:43 +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>
Link: https://lkml.kernel.org/r/20210420120705.5c705d4b@imladris.surriel.com
---
kernel/sched/fair.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1d75af1..83cd2bd 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();
@@ -10684,7 +10693,12 @@ out:
if (time_after(this_rq->next_balance, next_balance))
this_rq->next_balance = next_balance;
- if (pulled_task)
+ /*
+ * If we are no longer idle, do not let the time spent here pull
+ * down this_rq->avg_idle. That could lead to newidle_balance not
+ * doing enough work, and the CPU actually going idle.
+ */
+ if (pulled_task || this_rq->ttwu_pending)
this_rq->idle_stamp = 0;
else
nohz_newidle_balance(this_rq);
next prev parent reply other threads:[~2021-04-22 7:36 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-20 16:07 [PATCH v3] sched,fair: skip newidle_balance if a wakeup is pending Rik van Riel
2021-04-21 17:27 ` Vincent Guittot
2021-04-22 8:37 ` Vincent Guittot
2021-04-22 16:47 ` Rik van Riel
2021-04-22 7:36 ` tip-bot2 for Rik van Riel [this message]
2021-04-22 8:15 ` [tip: sched/core] " Peter Zijlstra
2021-04-22 17:02 [PATCH v4] sched,fair: Skip " Rik van Riel
2021-05-12 10:28 ` [tip: sched/core] " tip-bot2 for Rik van Riel
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