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From: <cl@rock-chips.com>
To: heiko@sntech.de
Cc: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
	vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
	rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
	akpm@linux-foundation.org, tglx@linutronix.de,
	mpe@ellerman.id.au, surenb@google.com, ben.dooks@codethink.co.uk,
	anshuman.khandual@arm.com, catalin.marinas@arm.com,
	will@kernel.org, keescook@chromium.org, luto@amacapital.net,
	wad@chromium.org, mark.rutland@arm.com, geert+renesas@glider.be,
	george_davis@mentor.com, sudeep.holla@arm.com,
	linux@armlinux.org.uk, gregkh@linuxfoundation.org,
	info@metux.net, kstewart@linuxfoundation.org,
	allison@lohutok.net, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, huangtao@rock-chips.com,
	Liang Chen <cl@rock-chips.com>
Subject: [PATCH v3 1/1] kthread: do not preempt current task if it is going to call schedule()
Date: Fri,  6 Mar 2020 15:01:33 +0800	[thread overview]
Message-ID: <20200306070133.18335-2-cl@rock-chips.com> (raw)
In-Reply-To: <20200306070133.18335-1-cl@rock-chips.com>

From: Liang Chen <cl@rock-chips.com>

when we create a kthread with ktrhead_create_on_cpu(),the child thread
entry is ktread.c:ktrhead() which will be preempted by the parent after
call complete(done) while schedule() is not called yet,then the parent
will call wait_task_inactive(child) but the child is still on the runqueue,
so the parent will schedule_hrtimeout() for 1 jiffy,it will waste a lot of
time,especially on startup.

  parent                             child
ktrhead_create_on_cpu()
  wait_fo_completion(&done) -----> ktread.c:ktrhead()
                             |----- complete(done);--wakeup and preempted by parent
 kthread_bind() <------------|  |-> schedule();--dequeue here
  wait_task_inactive(child)     |
   schedule_hrtimeout(1 jiffy) -|

So we hope the child just wakeup parent but not preempted by parent, and the
child is going to call schedule() soon,then the parent will not call
schedule_hrtimeout(1 jiffy) as the child is already dequeue.

The same issue for ktrhead_park()&&kthread_parkme().
This patch can save 120ms on rk312x startup with CONFIG_HZ=300.

Signed-off-by: Liang Chen <cl@rock-chips.com>
---
 kernel/kthread.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/kernel/kthread.c b/kernel/kthread.c
index b262f47046ca..bfbfa481be3a 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -199,8 +199,15 @@ static void __kthread_parkme(struct kthread *self)
 		if (!test_bit(KTHREAD_SHOULD_PARK, &self->flags))
 			break;
 
+		/*
+		 * Thread is going to call schedule(), do not preempt it,
+		 * or the caller of kthread_park() may spend more time in
+		 * wait_task_inactive().
+		 */
+		preempt_disable();
 		complete(&self->parked);
-		schedule();
+		schedule_preempt_disabled();
+		preempt_enable();
 	}
 	__set_current_state(TASK_RUNNING);
 }
@@ -245,8 +252,14 @@ static int kthread(void *_create)
 	/* OK, tell user we're spawned, wait for stop or wakeup */
 	__set_current_state(TASK_UNINTERRUPTIBLE);
 	create->result = current;
+	/*
+	 * Thread is going to call schedule(), do not preempt it,
+	 * or the creator may spend more time in wait_task_inactive().
+	 */
+	preempt_disable();
 	complete(done);
-	schedule();
+	schedule_preempt_disabled();
+	preempt_enable();
 
 	ret = -EINTR;
 	if (!test_bit(KTHREAD_SHOULD_STOP, &self->flags)) {
-- 
2.17.1




  reply	other threads:[~2020-03-06  7:02 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-06  7:01 [PATCH v3 0/1] wait_task_inactive() spend too much time on system startup cl
2020-03-06  7:01 ` cl [this message]
2020-03-06 17:09   ` [PATCH v3 1/1] kthread: do not preempt current task if it is going to call schedule() Steven Rostedt
2020-03-11 15:39   ` Peter Zijlstra
2020-03-20 12:58   ` [tip: sched/core] kthread: Do " tip-bot2 for Liang Chen

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