From: Andrew Morton <akpm@osdl.org>
To: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
Cc: nikita@clusterfs.com, nickpiggin@yahoo.com.au,
Linux-Kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH]: 1/4 batch mark_page_accessed()
Date: Wed, 1 Dec 2004 17:59:24 -0800 [thread overview]
Message-ID: <20041201175924.75cdcb83.akpm@osdl.org> (raw)
In-Reply-To: <20041201185827.GA5459@dmt.cyclades>
Marcelo Tosatti <marcelo.tosatti@cyclades.com> wrote:
>
> > I don't think that atomic_inc will be particularly
> > costly. generic_file_{write,read}() call find_get_page() just before
> > calling mark_page_accessed(), so cache-line with page reference counter
> > is most likely still exclusive owned by this CPU.
>
> Assuming that is true - what could cause the slowdown?
It isn't true. Atomic ops have a considerable overhead, and this is
unrelated to cache misses. This is especially true of p4's.
Now, that overhead may be justified. Needs more study.
WARNING: multiple messages have this Message-ID (diff)
From: Andrew Morton <akpm@osdl.org>
To: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
Cc: nikita@clusterfs.com, nickpiggin@yahoo.com.au,
Linux-Kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH]: 1/4 batch mark_page_accessed()
Date: Wed, 1 Dec 2004 17:59:24 -0800 [thread overview]
Message-ID: <20041201175924.75cdcb83.akpm@osdl.org> (raw)
In-Reply-To: <20041201185827.GA5459@dmt.cyclades>
Marcelo Tosatti <marcelo.tosatti@cyclades.com> wrote:
>
> > I don't think that atomic_inc will be particularly
> > costly. generic_file_{write,read}() call find_get_page() just before
> > calling mark_page_accessed(), so cache-line with page reference counter
> > is most likely still exclusive owned by this CPU.
>
> Assuming that is true - what could cause the slowdown?
It isn't true. Atomic ops have a considerable overhead, and this is
unrelated to cache misses. This is especially true of p4's.
Now, that overhead may be justified. Needs more study.
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next prev parent reply other threads:[~2004-12-02 2:00 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-11-21 15:44 [PATCH]: 1/4 batch mark_page_accessed() Nikita Danilov
2004-11-21 15:44 ` Nikita Danilov
2004-11-21 21:12 ` Andrew Morton
2004-11-21 21:12 ` Andrew Morton
2004-11-24 10:40 ` Marcelo Tosatti
2004-11-24 10:40 ` Marcelo Tosatti
2004-11-24 16:32 ` Marcelo Tosatti
2004-11-24 16:32 ` Marcelo Tosatti
2004-11-24 21:53 ` Nikita Danilov
2004-11-24 21:53 ` Nikita Danilov
2004-11-26 18:58 ` Marcelo Tosatti
2004-11-26 18:58 ` Marcelo Tosatti
2004-11-27 0:37 ` Nick Piggin
2004-11-27 0:37 ` Nick Piggin
2004-11-30 16:29 ` Marcelo Tosatti
2004-11-30 16:29 ` Marcelo Tosatti
2004-12-01 1:33 ` Andrew Morton
2004-12-01 1:33 ` Andrew Morton
2004-11-30 22:57 ` Marcelo Tosatti
2004-11-30 22:57 ` Marcelo Tosatti
2004-12-01 12:23 ` Nikita Danilov
2004-12-01 12:23 ` Nikita Danilov
2004-12-01 18:58 ` Marcelo Tosatti
2004-12-01 18:58 ` Marcelo Tosatti
2004-12-02 1:59 ` Andrew Morton [this message]
2004-12-02 1:59 ` Andrew Morton
2004-11-27 10:41 ` Nikita Danilov
2004-11-27 10:41 ` Nikita Danilov
2004-11-27 8:19 ` Marcelo Tosatti
2004-11-27 8:19 ` Marcelo Tosatti
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