linux-kernel - Re: current linux-2.6.git: cpusets completely broken

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Message-ID: <b647ffbd0807121619r15c2864fw5b0ff592ba8edbd2@mail.gmail.com>
Date:	Sun, 13 Jul 2008 01:19:09 +0200
From:	"Dmitry Adamushko" <dmitry.adamushko@...il.com>
To:	"Linus Torvalds" <torvalds@...ux-foundation.org>
Cc:	"Vegard Nossum" <vegard.nossum@...il.com>,
	"Paul Menage" <menage@...gle.com>,
	"Max Krasnyansky" <maxk@...lcomm.com>, "Paul Jackson" <pj@....com>,
	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>, miaox@...fujitsu.com,
	rostedt@...dmis.org, "Thomas Gleixner" <tglx@...utronix.de>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Linux Kernel" <linux-kernel@...r.kernel.org>
Subject: Re: current linux-2.6.git: cpusets completely broken

2008/7/13 Linus Torvalds <torvalds@...ux-foundation.org>:
>
>> (A little pet horse for the occasion: Testing can show the presence of
>> errors, but not their absence. But that's a different story.)
>
> Absolutely. Which is actually why I prefer my patch. I think it fixes - in
> general - the issue of CPU migration migrating tasks back to the CPU that
> we're taking down.
>
> The other patches seem to work around just the problem that _triggers_ the
> bug. They don't actually make it impossible to migrate to a CPU that is
> getting shut down - they just try to avoid the particular sequence that
> made it happen for you.

Well, they try to make sched-domains consistent for all possible
cases, not just any particular case. So no, they don't allow a
possibility to leave tasks on a dead CPU (unless there is another
bug).

With your patch (and a cpusets :: hotplug handler from the current
-git) sched-domains are still broken and they are used in a number of
places. So why keep them at all?

I'm really surprised that Vegard says this "cpu_active_map" patch
alone fixes the problem.

With your modifications of common_cpu_mem_hotplug_unplug() - yes but
then it will work even without "cpu_active_map".

(ok, unless I'm really blind at this late hour so please direct me to
the right way :-)


>
>                        Linus
>


-- 
Best regards,
Dmitry Adamushko
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