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

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Message-ID: <49D3B6CD.2030908@cosmosbay.com>
Date:	Wed, 01 Apr 2009 20:47:41 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
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

Jeremy Fitzhardinge a écrit :
> 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

Sure, but this saves one byte per call, this is probably why we still use
inc/dec in so many places...

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