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Date: Thu, 21 Oct 2010 15:43:33 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Nick Piggin <npiggin@kernel.dk>, Dave Chinner <david@fromorbit.com>,
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        Christoph Lameter <cl@linux-foundation.org>
Subject: Re: [PATCH] percpu_counter : add percpu_counter_add_fast()
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On Sat, 16 Oct 2010 16:19:14 +0200
Eric Dumazet <eric.dumazet@gmail.com> wrote:

> The current way to change a percpu_counter is to call
> percpu_counter_add(), which is a bit expensive.
> (More than 40 instructions, possible false sharing, ...)

This is incorrect.  With my compiler it's 25 instructions except in the
very rare case where a batch overflow occurs.

And more than half of that is function call entry/exit overhead.