linux-kernel - Re: [PATCH] stop_machine: disable preempt in stop machine path

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Message-Id: <20090916160358.7faadb5f.akpm@linux-foundation.org>
Date:	Wed, 16 Sep 2009 16:03:58 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Cc:	mingo@...e.hu, rusty@...tcorp.com.au, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] stop_machine: disable preempt in stop machine path

On Wed, 16 Sep 2009 15:26:54 +0800
Xiao Guangrong <xiaoguangrong@...fujitsu.com> wrote:

> We can disable preempt in stop_cpu(), It can reduce the cpu's waiting time
> and make stop_machine path faster.
> 

"it can"?  But does it?  Are there any measurements or observations to
back this up?

The kstop threads are already created with create_rt_workqueue() (which
has super-secret undocumented semantics which I have cleverly
discovered mean "use SCHED_FIFO").

So we won't be getting preempted here anyway?
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