linux-kernel - Re: [PATCH] percpu_counter : add percpu_counter_add

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Message-ID: <1287720725.7984.3.camel@edumazet-laptop>
Date:	Fri, 22 Oct 2010 06:12:05 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Christoph Lameter <cl@...ux.com>, Nick Piggin <npiggin@...nel.dk>,
	Dave Chinner <david@...morbit.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] percpu_counter : add percpu_counter_add_fast()

Le jeudi 21 octobre 2010 à 17:45 -0700, Andrew Morton a écrit :

> this_cpu_add_return() isn't really needed in this application.
> 
> {
> 	this_cpu_add(*fbc->counters, amount);
> 	if (unlikely(abs(this_cpu_read(*fbc->counters)) > fbc->batch))
> 		out_of_line_stuff();
> }	
> 
> will work just fine.				

Hmm, you cannot do this on 32bit machines because "amount" is 64bit
wide.

Switching counters to s64 is not an option (makes summation racy, and
memory use bigger)



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