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Subject: Re: 2.6.11-mm2
From: Robert Love <rlove@rlove.org>
To: "J.A. Magallon" <jamagallon@able.es>
Cc: linux-kernel@vger.kernel.org
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On Tue, 2005-03-08 at 23:36 +0000, J.A. Magallon wrote:

> Can cpu affinity really be changed for a running process ?

Yes.

> Does it need something like io or yielding to take effect ?

No.

> I am playin with Robert Love's taskset (symlinked to runon, it is easier
> to type and I'm more used to it), because I want to play with hyperthreading
> and wanted a method to force two threads on the same physical package.
> It works fine to bound a new process to a cpu set, but I does not change
> anything for a running process.
> 
> I try runon -c -p 0 <pid> for my numbercruncher and it does nothing, top
> shows it is in the same cpus where it started:
> 
> werewolf:~# runon -c -p 0 8277
> pid 8277's current affinity list: 0-3
> pid 8277's new affinity list: 0
> werewolf:~# runon -c -p 8277
> pid 8277's current affinity list: 0

This looks fine.  As expected.

Although, you have the syntax wrong.  It should be

	taskset -c 0 -p 8277

and

	taskset -p 8277

> The program uses posix threads, 2 in this case. The two threads change from
> cpu sometimes (not too often), but do not go into the same processor
> immediately as when I start the program directly with runon/taskset.

You have to bind all of the threads individually.

	Robert Love


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