From: Eric Dumazet <eric.dumazet@gmail.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Arjan van de Ven <arjan@infradead.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 22:24:41 +0200 [thread overview]
Message-ID: <4AC3BE89.3040708@gmail.com> (raw)
In-Reply-To: <alpine.LFD.2.01.0909301304310.6996@localhost.localdomain>
Linus Torvalds a écrit :
>
> On Wed, 30 Sep 2009, Arjan van de Ven wrote:
>> +ENTRY(cmpxchg8b_emu)
>> + CFI_STARTPROC
>> +
>> + push %edi
>> + push %ebx
>> + push %ecx
>> + /* disable interrupts */
>> + pushf
>> + pop %edi
>> + cli
>> +
>> + cmpl %edx, 4(%esi)
>> + jne 1f
>> + cmpl %eax, (%esi)
>> + jne 1f
>> +
>> + xchg (%esi), %ebx
>> + xchg 4(%esi), %ecx
>> + mov %ebx, %eax
>> + mov %ecx, %edx
>
> Ok, so why do you do this? You've just checked that the 8 bytes at esi are
> the same as edx:eax, why do you do that odd xchg?
>
> Why isn't this part just
>
> mov %ebx,(%esi)
> mov %ecx,4(%esi)
>
> and leave ebx/ecx alone?
>
> I also don't see why you play games with eflags and %edi. Just leave the
> flags on the stack. So it all would look like
>
> #
> # Emulate 'cmpxchg8b (%esi)' except we don't
> # set the whole ZF thing (caller will just
> # compare eax:edx with the expected value)
> #
> cmpxchg8b_emu:
> pushfl
> cli
> cmpl (%esi),%eax
> jne not_same
> cmpl 4(%esi),%edx
> jne not_same
> movl %ebx,(%esi)
> movl %ecx,4(%esi)
> popfl
> ret
> not_same:
> movl (%esi),%eax
> movl 4(%esi),%edx
> popfl
> ret
>
> I dunno. You _could_ use edi/ebp as a temporary for 'dest' to only do the
> load once (and add push/pop to save the registers), but it's not like the
> above is really atomic anyway, and it very much depends on 'cli' just
> making sure that nothing else happens. So the above seems to be the
> simplest emulation, considering the interfaces..
>
> UNTESTED! I wrote this in an email editor. I haven't assembled it or
> verified the semantics or workingness in any way, shape or form.
>
> Linus
Yes, I provided following version in my first answer but apparently it was too complex :)
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)
/* restore interrupts */
popf
ret
1:
mov (%esi), %eax
2:
mov 4(%esi), %edx
popf
ret
CFI_ENDPROC
ENDPROC(cmpxchg8b_emu)
next prev parent reply other threads:[~2009-09-30 20:25 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
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 [this message]
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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