linux-kernel - Re: [PATCH 1/2] scalable rw

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Date:	Sun, 13 May 2007 01:42:57 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <clameter@....com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH 1/2] scalable rw_mutex

On 05/12, Andi Kleen wrote:
>
> > This also allows us to de-uglify workqueue.c a little bit, it uses
> > a home-grown cpu_populated_map.
> 
> It might be obsolete iff more and more architecture don't use NR_CPUS filled
> possible_map anymore (haven't checked them all to know if it's true or not)
> 
> If not there are a couple of more optimizations that can be done, e.g.
> in networking by converting more code to hotplug notifier.

As for workqueue.c, it is not an optimization. It is a documentation.
For example, if CPU-hotplug use freezer, we can just do

	s/cpu_populated_map/cpu_online_map/

workqueue.c has a hotplug notifier, but we can't migrate work_structs
currently in a race-free manner.

So I vote for your patch in any case.

Oleg.

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