From: Ryan Cumming <bodnar42@phalynx.dhs.org>
To: Dave Jones <davej@suse.de>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [patch] Prefetching file_read_actor()
Date: Mon, 31 Dec 2001 12:40:19 -0800 [thread overview]
Message-ID: <E16L9EJ-0004Rf-00@phalynx> (raw)
In-Reply-To: <Pine.LNX.4.33.0112312045130.17274-100000@Appserv.suse.de>
In-Reply-To: <Pine.LNX.4.33.0112312045130.17274-100000@Appserv.suse.de>
On December 31, 2001 11:47, Dave Jones wrote:
> Completly puzzled right now. Moving the prefetching to copy_to_user
> (and doing the tlb preload & prefetching the whole chunk to be copied
> (or cachesize if smaller)) results in a performance drop instead of a win.
>
> My initial guess is that some of the callers of copy_to_user are
> doing something that is harmed the prefetching.
> (Maybe they are doing additional prefetch() calls)
Maybe syscalls that only have to move a very small chunk of data
(gettimeofday(2), for instance), are hurt because of the wasted bytes they
are prefetching after the intended data? Also, for sizes greater than 512,
copy_to_user will call mmx_copy_user, which might call mmx_memcpy, which does
prefetching already on x86 CPUs that support it.
-Ryan
next prev parent reply other threads:[~2001-12-31 20:40 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-12-31 3:32 [patch] Prefetching file_read_actor() Dave Jones
2001-12-31 5:44 ` Andrew Morton
2001-12-31 10:58 ` Manfred Spraul
2001-12-31 19:28 ` Andrew Morton
2001-12-31 19:47 ` Dave Jones
2001-12-31 20:40 ` Ryan Cumming [this message]
2002-01-01 10:29 ` Alan Cox
2002-01-01 12:45 ` Dave Jones
2002-01-01 15:26 ` Alan Cox
2002-01-01 10:30 ` Alan Cox
2002-01-01 11:08 ` Anton Blanchard
2001-12-31 20:31 ` Dave Jones
2001-12-31 13:00 ` Alan Cox
2001-12-31 12:50 ` Rik van Riel
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