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
next prev parent 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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