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From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: dada1@cosmosbay.com, mingo@elte.hu, htejun@gmail.com,
	linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
	joe@perches.com, rusty@rustcorp.com.au
Subject: Re: [PATCH] x86: percpu_to_op() misses memory and flags clobbers
Date: Thu, 02 Apr 2009 07:12:30 -0700	[thread overview]
Message-ID: <49D4C7CE.3060005@goop.org> (raw)
In-Reply-To: <20090402095217.GA30759@gondor.apana.org.au>

Herbert Xu wrote:
> Jeremy Fitzhardinge <jeremy@goop.org> wrote:
>   
>> 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.
>>     
>
> Is this still the case on the latest Intel CPUs?
>   

Yes:

    Assembly/Compiler Coding Rule 32. (M impact, H generality) INC and DEC
    instructions should be replaced with ADD or SUB instructions,
    because ADD and
    SUB overwrite all flags, whereas INC and DEC do not, therefore
    creating false
    dependencies on earlier instructions that set the flags.

    J

  reply	other threads:[~2009-04-02 14:12 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-04-01  8:13 [PATCH] x86: percpu_to_op() misses memory and flags clobbers Eric Dumazet
2009-04-01  9:02 ` Jeremy Fitzhardinge
2009-04-01 10:14   ` Eric Dumazet
2009-04-01 16:12     ` Ingo Molnar
2009-04-01 16:41       ` Jeremy Fitzhardinge
2009-04-01 16:44         ` Ingo Molnar
2009-04-01 17:13       ` Eric Dumazet
2009-04-01 18:07         ` Jeremy Fitzhardinge
2009-04-01 18:47           ` Eric Dumazet
2009-04-02  9:52           ` Herbert Xu
2009-04-02 14:12             ` Jeremy Fitzhardinge [this message]
2009-04-01 18:44         ` [RFC] percpu: convert SNMP mibs to new infra Eric Dumazet
2009-04-02  0:13           ` Tejun Heo
2009-04-02  4:05             ` Ingo Molnar
2009-04-02  8:07               ` [PATCH] " Eric Dumazet
2009-04-03  0:39                 ` Tejun Heo
2009-04-03 17:10                 ` Ingo Molnar
2009-04-02  5:04           ` [RFC] " Rusty Russell
2009-04-02  5:19             ` Eric Dumazet
2009-04-02 11:46               ` Rusty Russell

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