linux-kernel - Re: [PATCH 1/1] kthread: disable preemption during complete()

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Message-ID: <20120726155409.GB20964@redhat.com>
Date:	Thu, 26 Jul 2012 17:54:09 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Peter Zijlstra <peterz@...radead.org>, Tejun Heo <tj@...nel.org>,
	Peter Boonstoppel <pboonstoppel@...dia.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Henrique de Moraes Holschuh <ibm-acpi@....eng.br>,
	Andy Walls <awalls@...metrocast.net>,
	Diwakar Tundlam <dtundlam@...dia.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 1/1] kthread: disable preemption during complete()

On 07/26, Thomas Gleixner wrote:
>
> On Thu, 26 Jul 2012, Peter Zijlstra wrote:
> > On Wed, 2012-07-25 at 15:40 -0700, Tejun Heo wrote:
> > > > This patch disables preemption during complete(), since we call
> > > > schedule() directly afterwards, so it will correctly enter
> > > > TASK_UNINTERRUPTIBLE. This speeds up kthread creation/binding during
> > > > cpu hotplug significantly.
> >
> > tglx has patches that make the kthread create/destroy stuff from hotplug
> > go away.. that seems like the better approach.
>
> Right. That cpu hotplug setup/teardown stuff is ugly.

Could you cc me if you send these patches?

> > The comment doesn't really make that clear.
>
> Right, the comment is crap. It has nothing to do with kthread_bind()
> and stuff. The whole purpose is to avoid the pointless preemption
> after wakeup.

Yes, but this "avoid the preemption after wakeup" can actually help
kthread_bind()->wait_task_inactive() ?

This reminds me, Peter had a patch which teaches wait_task_inactive()
to use sched_in/sched_out notifiers to avoid the polling...

Oleg.

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