Subject: Re: [PATCH] migration thread fix
From: Robert Love <rml@tech9.net>
To: William Lee Irwin III <wli@holomorphy.com>
Cc: Erich Focht <efocht@ess.nec.de>, linux-kernel@vger.kernel.org,
        Ingo Molnar <mingo@elte.hu>, torvalds@transmeta.com
In-Reply-To: <20020418212851.GW21206@holomorphy.com>
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Date: 18 Apr 2002 17:41:04 -0400
Message-Id: <1019166066.5395.99.camel@phantasy>
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Sender: linux-kernel-owner@vger.kernel.org

On Thu, 2002-04-18 at 17:28, William Lee Irwin III wrote:
> I have a patch to fix #2 as well. Did you see it? Did you try it?

Eric, I am interested in your opinion of wli's patch, too.  I really
liked his approach.

You seem to remove a lot of code since, after starting the first thread,
you rely on set_cpus_allowed and the existing migration_thread to push
the task to the correct place.  I suppose this will work .. but it may
depend implicitly on behavior of the migration_threads and load_balance
(not that the current code doesn't rely on load_balance - it does).

What happens if a migration_thread comes up on a CPU without a migration
thread and then you call set_cpus_allowed?

I am also curious what causes #1 you mention.  Do you see it in the
_normal_ code or just with your patch?  I cannot see what we race
against wrt interrupts ... disabling interrupts, however, would disable
load_balance and that is a potential pitfall with using
migration_threads to migrate migration_threads as noted above.

	Robert Love

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