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From: Arjan van de Ven <arjan@infradead.org>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	John Stultz <johnstul@us.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Ingo Molnar <mingo@elte.hu>
Subject: Re: Linux 2.6.32-rc1
Date: Wed, 30 Sep 2009 17:31:02 +0200	[thread overview]
Message-ID: <20090930173102.2d54534c@infradead.org> (raw)
In-Reply-To: <4AC378C9.5050507@gmail.com>

On Wed, 30 Sep 2009 17:27:05 +0200
Eric Dumazet <eric.dumazet@gmail.com> wrote:
> 
> > +	pop %edi
> Why do you pop flags in edi, to later re-push them ?
> 
> > +	cli

because here I disable interrupts

(basically this is local_irq_save() )
> 
> 
> > +	xchg (%esi), %ebx
> > +	xchg 4(%esi), %ecx
> How this sequence is guaranteed to be atomic with other cpus ?

it is not. this is the 486 implementation which is !SMP
(just like the current cmpxchg64() fallback)

> 
> If it is a !SMP implementation, then you could replace xchg by mov
> instructions.

that is not equivalent. I need to also store the old values
and return them....


> 
> So I suggest :
> 
> 
> ENTRY(cmpxchg8b_emu)
> 	CFI_STARTPROC
> 
> 	/* disable interrupts */
> 	pushf
> 	cli
> 
> 	cmpl  %eax,(%esi)
> 	jne   1f
> 	cmpl  %edx,4(%esi)
> 	jne   2f
> 
> 	mov   %ebx,(%esi)
> 	mov   %ecx,4(%esi)

this is not equivalent since you don't return the "prev" value.



-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org

  reply	other threads:[~2009-09-30 15:30 UTC|newest]

Thread overview: 80+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-09-27 22:34 Linux 2.6.32-rc1 Linus Torvalds
2009-09-27 23:44 ` Stephen Rothwell
2009-09-27 23:48   ` Diego Calleja
2009-09-27 23:52   ` Linus Torvalds
2009-09-28  0:17     ` Stephen Rothwell
2009-09-28  7:07 ` Eric Dumazet
2009-09-28 15:39   ` Linus Torvalds
2009-09-28 17:15     ` Martin Schwidefsky
2009-09-28 18:41       ` Eric Dumazet
2009-09-28 20:56         ` Martin Schwidefsky
2009-09-29 20:42         ` Eric Dumazet
2009-09-29 21:17           ` Linus Torvalds
2009-09-29 21:22             ` Arjan van de Ven
2009-09-29 21:56               ` Linus Torvalds
2009-09-30 15:07                 ` Arjan van de Ven
2009-09-30 15:27                   ` Eric Dumazet
2009-09-30 15:31                     ` Arjan van de Ven [this message]
2009-10-01  0:42                       ` Yuhong Bao
2009-09-30 15:57                   ` Eric Dumazet
2009-09-30 16:13                     ` Arjan van de Ven
2009-09-30 16:14                     ` Linus Torvalds
2009-09-30 18:53                       ` Ingo Molnar
2009-09-30 22:03                         ` [GIT PULL] scheduler fixes Ingo Molnar
2009-10-01  0:42                           ` Linus Torvalds
2009-10-01  0:57                             ` Linus Torvalds
2009-10-01  5:30                               ` Eric Dumazet
2009-10-01  6:11                                 ` Ingo Molnar
2009-10-01  6:18                                   ` Eric Dumazet
2009-10-01  6:42                                     ` Ingo Molnar
2009-10-01  6:59                                       ` Eric Dumazet
2009-10-01  7:28                                       ` Sam Ravnborg
2009-10-01  6:49                                 ` [tip:x86/urgent] x86: Don't generate cmpxchg8b_emu if CONFIG_X86_CMPXCHG64=y tip-bot for Eric Dumazet
2009-10-01  6:40                               ` [tip:x86/urgent] x86: Optimize cmpxchg64() at build-time some more tip-bot for Linus Torvalds
2009-10-02 16:40                               ` [GIT PULL] scheduler fixes Yuhong Bao
2009-10-01  6:05                             ` Ingo Molnar
2009-09-30 16:14                     ` Linux 2.6.32-rc1 Cyrill Gorcunov
2009-09-30 16:55                   ` Stefan Richter
2009-09-30 17:08                     ` Linus Torvalds
2009-09-30 17:40                       ` Stefan Richter
2009-09-30 19:32                   ` Ingo Molnar
2009-09-30 19:35                     ` Ingo Molnar
2009-09-30 20:16                     ` Eric Dumazet
2009-09-30 20:20                       ` Linus Torvalds
2009-09-30 20:22                         ` Ingo Molnar
2009-09-30 20:38                           ` Ingo Molnar
2009-10-01  7:18                             ` Arjan van de Ven
2009-09-30 19:37                   ` [tip:sched/urgent] x86: Provide an alternative() based cmpxchg64() tip-bot for Arjan van de Ven
2009-09-30 19:37                   ` [tip:sched/urgent] sched_clock: Fix atomicity/continuity bug by using cmpxchg64() tip-bot for Arjan van de Ven
2009-09-30 19:39                     ` Ingo Molnar
2009-09-30 19:39                   ` tip-bot for Eric Dumazet
2009-09-30 20:19                   ` Linux 2.6.32-rc1 Linus Torvalds
2009-09-30 20:24                     ` Eric Dumazet
2009-09-30 20:41                       ` Linus Torvalds
2009-09-30 20:49                         ` Ingo Molnar
2009-09-30 20:53                           ` Eric Dumazet
2009-09-30 21:00                             ` Ingo Molnar
2009-09-30 20:54                         ` Linus Torvalds
2009-09-30 21:53                         ` David Miller
2009-10-01 12:48                         ` Christoph Hellwig
2009-10-01 16:08                           ` Valdis.Kletnieks
2009-10-05 14:39                             ` Peter Zijlstra
2009-09-30 20:40                   ` [tip:sched/urgent] x86: Provide an alternative() based cmpxchg64() tip-bot for Arjan van de Ven
2009-09-30 20:58                     ` Ingo Molnar
2009-09-30 20:40                   ` [tip:sched/urgent] sched_clock: Fix atomicity/continuity bug by using cmpxchg64() tip-bot for Eric Dumazet
2009-09-30 20:55                   ` [tip:sched/urgent] x86: Provide an alternative() based cmpxchg64() tip-bot for Arjan van de Ven
2009-09-30 20:55                   ` [tip:sched/urgent] sched_clock: Fix atomicity/continuity bug by using cmpxchg64() tip-bot for Eric Dumazet
2009-09-30 21:00                   ` [tip:sched/urgent] x86: Provide an alternative() based cmpxchg64() tip-bot for Arjan van de Ven
2009-09-30 21:01                   ` [tip:sched/urgent] sched_clock: Fix atomicity/continuity bug by using cmpxchg64() tip-bot for Eric Dumazet
2009-10-05 16:00             ` [PATCH] x86: Generate cmpxchg build failures Peter Zijlstra
2009-10-05 18:51               ` Maciej Żenczykowski
2009-10-05 19:16               ` Linus Torvalds
2009-10-05 19:33                 ` Peter Zijlstra
2009-10-05 20:54                   ` Linus Torvalds
2009-10-09 14:23                   ` [tip:x86/asm] " tip-bot for Peter Zijlstra
2009-09-28 14:34 ` Linux 2.6.32-rc1 compile error Wolfgang Erig
2009-09-28 15:10   ` Jaswinder Singh Rajput
2009-09-28 15:32     ` Wolfgang Erig
2009-09-28 16:25 ` [PATCH] isdn: fix netjet/isdnhdlc build errors Randy Dunlap
2009-09-28 19:47   ` David Miller
  -- strict thread matches above, loose matches on Subject: below --
2009-09-28 22:10 Linux 2.6.32-rc1 devzero

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