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From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Arjan van de Ven <arjan@infradead.org>,
	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 20:14:47 +0400	[thread overview]
Message-ID: <20090930161447.GC5235@lenovo> (raw)
In-Reply-To: <4AC37FE5.7020200@gmail.com>

[Eric Dumazet - Wed, Sep 30, 2009 at 05:57:25PM +0200]
...
| 
| > +#define cmpxchg64(ptr, o, n)					\
| > +({								\
| > +	__typeof__(*(ptr)) __ret;				\
| > +	__typeof__(*(ptr)) __old = (o);				\
| > +	__typeof__(*(ptr)) __new = (n);				\
| > +	alternative_io("call cmpxchg8b_emu",			\
| > +			"lock; cmpxchg8b (%%esi)" ,		\
| > +		       X86_FEATURE_CX8,				\
| > +		       "=A" (__ret),				\
| > +		       "S" ((ptr)), "0" (__old),		\
| > +		       "b" ((unsigned int)__new),		\
| > +		       "c" ((unsigned int)(__new>>32)));	\
| 
| 
| Note:
| 
| lock; cmpxchg8b (%%esi)
| 
| gives 4 bytes opcode : f0 0f c7 0e
| Because alternative (call cmpxchg8b_emu) uses 5 bytes, a nop will be added.
| 
| Choosing ".byte 0xf0, 0x0f, 0xc7, 0x4e, 0x00"  aka "lock cmpxchg8b 0x0(%esi)" is a litle bit better ?
| 

Just curious why not "nop; lock; cmpxchg8b (%esi)"? lock itself is destructive
instruction with causes write buffers to flush data back and NOP itself will
be discarded by cpu internals so I suppose this form should be better. Though
I could miss something, and OTOH it's not a big deal. But still curious :)

	-- Cyrill

  parent reply	other threads:[~2009-09-30 16:14 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                     ` Cyrill Gorcunov [this message]
2009-09-30 16:55                   ` Linux 2.6.32-rc1 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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