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

[Oleg Nesterov]

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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