From: "tip-bot2 for Liang Chen" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Liang Chen <cl@rock-chips.com>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
"Steven Rostedt (VMware)" <rostedt@goodmis.org>,
x86 <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>
Subject: [tip: sched/core] kthread: Do not preempt current task if it is going to call schedule()
Date: Fri, 20 Mar 2020 12:58:03 -0000 [thread overview]
Message-ID: <158470908349.28353.3855924848715964020.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20200306070133.18335-2-cl@rock-chips.com>
The following commit has been merged into the sched/core branch of tip:
Commit-ID: 26c7295be0c5e6da3fa45970e9748be983175b1b
Gitweb: https://git.kernel.org/tip/26c7295be0c5e6da3fa45970e9748be983175b1b
Author: Liang Chen <cl@rock-chips.com>
AuthorDate: Fri, 06 Mar 2020 15:01:33 +08:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Fri, 20 Mar 2020 13:06:20 +01:00
kthread: Do not preempt current task if it is going to call schedule()
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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Link: https://lkml.kernel.org/r/20200306070133.18335-2-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 b262f47..bfbfa48 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)) {
prev parent reply other threads:[~2020-03-20 12:58 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 ` [PATCH v3 1/1] kthread: do not preempt current task if it is going to call schedule() cl
2020-03-06 17:09 ` Steven Rostedt
2020-03-11 15:39 ` Peter Zijlstra
2020-03-20 12:58 ` tip-bot2 for Liang Chen [this message]
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