From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 03/19] fs: Convert nr_inodes and nr_unused to per-cpu
 counters
Date: Sat, 16 Oct 2010 19:26:48 +0200
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Cc: Dave Chinner <david@fromorbit.com>, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org
To: Eric Dumazet <eric.dumazet@gmail.com>
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On Sat, 2010-10-16 at 12:27 +0200, Eric Dumazet wrote:
> 
> In cases you mention, you want a precise count (aka
> percpu_counter_sum_positive()), not the approximate one (aka
> percpu_counter_read_positive()).
> 
> The only difference is then the possible/online cpu loop difference.
> 
In either case, SGI is screwed, doing millions of for_each_*_cpu() loops
per second isn't going to work for them.

fwiw, for_each_*_cpu() takes longer than a single jiffy tick on those
machines.