From: "Chen, Kenneth W" <kenneth.w.chen@intel.com>
To: 'Christoph Lameter' <clameter@sgi.com>
Cc: 'Nick Piggin' <nickpiggin@yahoo.com.au>,
'Zoltan Menyhart' <Zoltan.Menyhart@bull.net>,
"'Boehm, Hans'" <hans.boehm@hp.com>,
"'Grundler, Grant G'" <grant.grundler@hp.com>,
akpm@osdl.org, linux-kernel@vger.kernel.org,
linux-ia64@vger.kernel.org
Subject: RE: Synchronizing Bit operations V2
Date: Fri, 31 Mar 2006 03:02:00 +0000 [thread overview]
Message-ID: <200603310301.k2V31Gg28423@unix-os.sc.intel.com> (raw)
In-Reply-To: <Pine.LNX.4.64.0603301855280.3045@schroedinger.engr.sgi.com>
In-Reply-To: <Pine.LNX.4.64.0603301615540.2023@schroedinger.engr.sgi.com>
Christoph Lameter wrote on Thursday, March 30, 2006 6:56 PM
> > By the way, this is the same thing on x86: look at include/asm-i386/bitops.h:
> >
> > #define smp_mb__before_clear_bit() barrier()
> > #define smp_mb__after_clear_bit() barrier()
> >
> > A simple compiler barrier, nothing but
> > #define barrier() __asm__ __volatile__("": : :"memory")
> >
> > See, no memory ordering there, because clear_bit already has a LOCK prefix.
>
> And that implies barrier behavior right?
No, not the memory ordering semantics you are thinking about. It just tell
compiler not to be over smart and schedule a load operation above that point
Intel compiler is good at schedule memory load way ahead of its use to hide
memory latency. gcc probably does that too, I'm not 100% sure. This prevents
the compiler to schedule load before that line.
- Ken
next prev parent reply other threads:[~2006-03-31 3:02 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-03-30 21:02 Bit operations with the ability to specify a synchronization mode Christoph Lameter
2006-03-31 0:18 ` Synchronizing Bit operations V2 Christoph Lameter
2006-03-31 0:39 ` Chen, Kenneth W
2006-03-31 0:42 ` Christoph Lameter
2006-03-31 0:45 ` Christoph Lameter
2006-03-31 0:42 ` David Mosberger-Tang
2006-03-31 0:49 ` Christoph Lameter
2006-03-31 6:10 ` Chris Wright
2006-03-31 0:44 ` Nick Piggin
2006-03-31 3:28 ` Christoph Lameter
2006-03-31 4:12 ` Nick Piggin
2006-03-31 17:43 ` Christoph Lameter
2006-04-01 2:56 ` Nick Piggin
2006-03-31 0:50 ` Chen, Kenneth W
2006-03-31 0:51 ` Christoph Lameter
2006-03-31 0:53 ` Chen, Kenneth W
2006-03-31 0:55 ` Christoph Lameter
2006-03-31 0:56 ` Luck, Tony
2006-03-31 0:58 ` Christoph Lameter
2006-04-02 7:59 ` Russell King
2006-03-31 0:59 ` Chen, Kenneth W
2006-03-31 1:09 ` Christoph Lameter
2006-03-31 1:04 ` Chen, Kenneth W
2006-03-31 1:13 ` Christoph Lameter
2006-03-31 1:13 ` Chen, Kenneth W
2006-03-31 1:29 ` Chen, Kenneth W
2006-03-31 1:37 ` Christoph Lameter
2006-03-31 1:33 ` linux
2006-03-31 1:40 ` Christoph Lameter
2006-03-31 2:35 ` Chen, Kenneth W
2006-03-31 2:37 ` Christoph Lameter
2006-03-31 2:45 ` Chen, Kenneth W
2006-03-31 2:53 ` Nick Piggin
2006-03-31 3:01 ` Christoph Lameter
2006-03-31 2:51 ` Chen, Kenneth W
2006-03-31 2:55 ` Christoph Lameter
2006-03-31 3:02 ` Chen, Kenneth W [this message]
2006-03-31 3:08 ` Christoph Lameter
2006-03-31 3:10 ` Chen, Kenneth W
2006-03-31 3:12 ` Christoph Lameter
2006-03-31 3:11 ` Chen, Kenneth W
2006-03-31 3:14 ` Chen, Kenneth W
2006-03-31 3:20 ` Christoph Lameter
2006-03-31 3:17 ` Chen, Kenneth W
2006-03-31 3:23 ` Chen, Kenneth W
2006-03-31 3:37 ` Chen, Kenneth W
2006-03-31 6:15 ` Chen, Kenneth W
2006-03-31 7:34 ` Nick Piggin
2006-03-31 13:28 ` Andi Kleen
2006-03-31 16:22 ` Hans Boehm
2006-03-31 16:37 ` Andi Kleen
2006-03-31 17:46 ` Christoph Lameter
2006-03-31 17:45 ` Christoph Lameter
2006-03-31 17:48 ` Andi Kleen
2006-03-31 17:56 ` Christoph Lameter
2006-04-02 7:54 ` Russell King
2006-03-31 18:57 ` Chen, Kenneth W
2006-03-31 19:41 ` Chen, Kenneth W
2006-03-31 21:15 ` Christoph Lameter
2006-03-31 21:24 ` Chen, Kenneth W
2006-03-31 21:28 ` Christoph Lameter
2006-04-01 2:16 ` Nick Piggin
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