From: Phillip Susi <psusi@cfl.rr.com>
To: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
"Kleen, Andi" <ak@suse.de>
Subject: Re: Is gcc thread-unsafe?
Date: Wed, 31 Oct 2007 18:10:20 -0400 [thread overview]
Message-ID: <4728FD4C.2010509@cfl.rr.com> (raw)
In-Reply-To: <200710251324.49888.nickpiggin@yahoo.com.au>
> pushl %ebp
> movl %esp, %ebp
> cmpl $0, 8(%ebp)
> movl $1, %eax
> cmove v, %eax ; load (maybe)
> movl %eax, v ; store (always)
> popl %ebp
> ret
How is this even an optimization? It looks SLOWER to me. The
conditional read wastes memory bandwidth sometimes, if the condition is
true, and v isn't already in the cache. The unconditional write wastes
memory bandwidth ALL the time, and dirties/flushes caches, in addition
to not being thread safe.
This SHOULD be using a conditional write instead of a conditional read
and an unconditional write.
next prev parent reply other threads:[~2007-10-31 22:10 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-10-25 3:24 Is gcc thread-unsafe? Nick Piggin
2007-10-25 3:46 ` Arjan van de Ven
2007-10-25 3:58 ` Nick Piggin
2007-10-25 4:29 ` David Schwartz
2007-10-25 4:35 ` Arjan van de Ven
2007-10-25 18:45 ` Måns Rullgård
2007-10-25 4:47 ` Nick Piggin
2007-10-25 9:40 ` Samuel Tardieu
2007-10-25 9:44 ` Samuel Tardieu
2007-10-25 9:54 ` Samuel Tardieu
2007-10-25 9:55 ` Andi Kleen
2007-10-25 7:15 ` Andi Kleen
2007-10-25 11:58 ` linux-os (Dick Johnson)
2007-10-25 12:16 ` Andi Kleen
2007-10-25 22:49 ` Nick Piggin
2007-10-25 23:09 ` Andi Kleen
2007-10-25 23:14 ` Linus Torvalds
2007-10-25 23:16 ` Andi Kleen
2007-10-25 23:32 ` Linus Torvalds
2007-10-25 23:42 ` Andi Kleen
2007-10-25 23:57 ` Linus Torvalds
2007-10-26 1:15 ` Zachary Amsden
2007-10-26 4:57 ` Willy Tarreau
2007-10-25 23:43 ` Nick Piggin
2007-10-25 23:55 ` Andi Kleen
2007-10-25 23:57 ` Nick Piggin
2007-10-25 14:55 ` Linus Torvalds
2007-10-25 15:12 ` Pekka Enberg
2007-10-25 21:42 ` David Schwartz
2007-10-25 23:22 ` Nick Piggin
2007-10-26 11:59 ` Andrew Haley
2007-10-26 11:59 ` Andrew Haley
2007-10-26 17:39 ` Chris Friesen
2007-10-25 22:26 ` Ismail Dönmez
2007-10-25 22:56 ` Jeff Garzik
2007-10-25 23:04 ` Jeff Garzik
2007-10-31 22:10 ` Phillip Susi [this message]
[not found] <fa.JbRGo0cQWncrcfKHmiNdvchsA50@ifi.uio.no>
[not found] ` <fa.8qDECVaPIo7DWbjhQbyw6N5Infg@ifi.uio.no>
[not found] ` <fa.M4DOMggyrQmdTqekWSuw4xCxiTc@ifi.uio.no>
2007-10-25 23:27 ` Robert Hancock
[not found] <e2e108260710260729x4603211cgb68d7434ce1e54e9@mail.gmail.com>
2007-10-26 14:40 ` Bart Van Assche
2007-10-26 15:09 ` Linus Torvalds
2007-10-26 15:34 ` Andrew Haley
2007-10-26 18:06 ` David Schwartz
2007-10-30 10:20 ` Andrew Haley
2007-11-02 15:29 ` Bart Van Assche
2007-11-02 15:38 ` Andrew Haley
2007-11-04 15:13 ` Bart Van Assche
2007-11-04 17:45 ` Linus Torvalds
2007-11-04 17:58 ` Andrew Haley
2007-11-04 18:06 ` Bart Van Assche
2007-11-02 17:18 ` David Schwartz
2007-10-26 21:45 ` Giacomo Catenazzi
2007-10-26 22:24 ` Linus Torvalds
2007-10-26 15:27 ` Linus Torvalds
2007-10-26 16:28 ` Linus Torvalds
2007-10-26 17:07 ` Bart Van Assche
2007-10-26 17:12 ` Andrew Haley
2007-10-26 17:25 ` Linus Torvalds
2007-10-26 18:08 ` Alan Cox
2007-10-26 18:14 ` Linus Torvalds
2007-10-26 20:39 ` Andi Kleen
-- strict thread matches above, loose matches on Subject: below --
2007-10-28 18:19 linux
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