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

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Message-Id: <20070511110522.ed459635.akpm@linux-foundation.org>
Date:	Fri, 11 May 2007 11:05:22 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Christoph Lameter <clameter@....com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...sign.ru>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH 1/2] scalable rw_mutex

On Fri, 11 May 2007 10:07:17 -0700 (PDT)
Christoph Lameter <clameter@....com> wrote:

> On Fri, 11 May 2007, Andrew Morton wrote:
> 
> > yipes.  percpu_counter_sum() is expensive.
> 
> Capable of triggering NMI watchdog on 4096+ processors?

Well.  That would be a millisecond per cpu which sounds improbable.  And
we'd need to be calling it under local_irq_save() which we presently don't.
And nobody has reported any problems against the existing callsites.

But it's no speed demon, that's for sure.
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