linux-kernel - Re: [PATCH] x86: percpu_to_op() misses memory and flags clobbers

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Message-ID: <49D3AD61.5090206@goop.org>
Date:	Wed, 01 Apr 2009 11:07:29 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Eric Dumazet <dada1@...mosbay.com>
CC:	Ingo Molnar <mingo@...e.hu>, Tejun Heo <htejun@...il.com>,
	linux kernel <linux-kernel@...r.kernel.org>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Joe Perches <joe@...ches.com>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH] x86: percpu_to_op() misses memory and flags clobbers

Eric Dumazet wrote:
> +#define percpu_inc(var)		percpu_to_op0("inc", per_cpu__##var)
> +#define percpu_dec(var)		percpu_to_op0("dec", per_cpu__##var)
>   

There's probably not a lot of value in this.  The Intel and AMD 
optimisation guides tend to deprecate inc/dec in favour of using 
add/sub, because the former can cause pipeline stalls due to its partial 
flags update.

    J
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