From: Linus Torvalds <torvalds@linux-foundation.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: mikulas@artax.karlin.mff.cuni.cz, viro@zeniv.linux.org.uk,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH]: Fix SMP-reordering race in mark_buffer_dirty
Date: Wed, 2 Apr 2008 15:07:22 -0700 (PDT) [thread overview]
Message-ID: <alpine.LFD.1.00.0804021505160.14670@woody.linux-foundation.org> (raw)
In-Reply-To: <20080402150158.f366370f.akpm@linux-foundation.org>
On Wed, 2 Apr 2008, Andrew Morton wrote:
>
> But then the test-and-set of an already-set flag would newly cause the
> cacheline to be dirtied, requiring additional bus usage to write it back?
>
> The CPU's test-and-set-bit operation could of course optimise that away in
> this case. But does it?
No, afaik no current x86 uarch will optimize away the write on a locked
instuction if it turns out to be unnecessary.
Can somebody find a timing reason to have the ugly code?
Linus
next prev parent reply other threads:[~2008-04-02 22:08 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-04-02 19:20 Mikulas Patocka
2008-04-02 19:44 ` Linus Torvalds
2008-04-02 21:03 ` Mikulas Patocka
2008-04-02 21:31 ` Linus Torvalds
2008-04-02 21:35 ` Linus Torvalds
2008-04-02 22:39 ` Mikulas Patocka
2008-04-02 22:51 ` Linus Torvalds
2008-04-02 22:35 ` Mikulas Patocka
2008-04-02 22:01 ` Andrew Morton
2008-04-02 22:07 ` Linus Torvalds [this message]
2008-04-02 22:53 ` Mikulas Patocka
2008-04-02 23:52 ` Linus Torvalds
2008-04-03 2:12 ` Andrew Morton
2008-04-03 14:34 ` Linus Torvalds
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