linux-kernel - [PATCH 4/8] sched/core: Skip wakeup when task is already running.

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Date:	Tue, 15 Apr 2014 21:32:53 +0900
From:	Dongsheng Yang <yangds.fnst@...fujitsu.com>
To:	<rostedt@...dmis.org>, <fweisbec@...il.com>, <mingo@...hat.com>,
	<peterz@...radead.org>, <acme@...stprotocols.net>
CC:	<linux-kernel@...r.kernel.org>,
	Dongsheng <yangds.fnst@...fujitsu.com>
Subject: [PATCH 4/8] sched/core: Skip wakeup when task is already running.

From: Dongsheng <yangds.fnst@...fujitsu.com>

It is pointless to wake up a running task. Currently, we can
see it in perf sched latency.

	# perf sched record sleep 10
	[ perf record: Woken up 2 times to write data ]
	[ perf record: Captured and wrote 21.170 MB perf.data (~924950 samples) ]
	# perf sched latency |tail
	  ksoftirqd/13:57       |      0.011 ms |        1 | avg:    0.003 ms | max:    0.003 ms | max at: 254123.512011 s
	  khelper:6423          |      0.059 ms |        3 | avg:    0.003 ms | max:    0.005 ms | max at: 254124.947110 s
	  ksoftirqd/3:17        |      0.042 ms |        2 | avg:    0.003 ms | max:    0.003 ms | max at: 254126.478175 s
	  automount:6465        |      0.480 ms |        1 | avg:    0.000 ms | max:    0.000 ms | max at:  0.000000 s
	  automount:6618        |      0.465 ms |        1 | avg:    0.000 ms | max:    0.000 ms | max at:  0.000000 s
	 -----------------------------------------------------------------------------------------
	  TOTAL:                |   3535.020 ms |    28477 |
	 ---------------------------------------------------
	  INFO: 0.922% state machine bugs (259 out of 28092)

Signed-off-by: Dongsheng <yangds.fnst@...fujitsu.com>
---
 kernel/sched/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 268a45e..fc6b644 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1416,6 +1416,9 @@ static void ttwu_activate(struct rq *rq, struct task_struct *p, int en_flags)
 static void
 ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags)
 {
+	if (p->state == TASK_RUNNING)
+		return;
+
 	check_preempt_curr(rq, p, wake_flags);
 	trace_sched_wakeup(p, true);
 
-- 
1.8.2.1

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