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Date: Fri, 11 May 2007 11:05:22 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Christoph Lameter <clameter@sgi.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, linux-mm@kvack.org,
       linux-kernel@vger.kernel.org, Oleg Nesterov <oleg@tv-sign.ru>,
       Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
       Nick Piggin <npiggin@suse.de>
Subject: Re: [PATCH 1/2] scalable rw_mutex
Message-Id: <20070511110522.ed459635.akpm@linux-foundation.org>
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On Fri, 11 May 2007 10:07:17 -0700 (PDT)
Christoph Lameter <clameter@sgi.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.