Subject: Re: preemption when running in the kernel
From: Robert Love <rml@tech9.net>
To: Frank Cusack <fcusack@fcusack.com>
Cc: Ingo Oeser <ioe-lkml@rameria.de>, linux-kernel@vger.kernel.org
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Date: Sun, 09 Nov 2003 12:56:40 -0500
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On Sun, 2003-11-09 at 05:04, Frank Cusack wrote:

> Thank you for the clarification.

No problem.

> That leads me to 2 followup questions.
> 
> If a task in the kernel is preempted, is a membar issued?  (I believe
> so -- running another task means that the scheduler must have run,
> which will grab and release various locks thus giving us the membars.)

Yes, a memory barrier is definitely issued.

> When the preempted task resumes, is it guaranteed to run on the same CPU?
> (I wouldn't expect so, unless the task was specifically told to do that
> via hard affinity.  But maybe a task preempted in the kernel is different
> then a task preempted in userland.)

No.  A preempted task can reschedule on any processor.

	Robert Love


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