From: Andrew Morton <akpm@osdl.org>
To: Hanna Linder <hannal@us.ibm.com>
Cc: lse-tech@lists.sourceforge.net, linux-kernel@vger.kernel.org
Subject: Re: Minutes from 10/1 LSE Call
Date: Wed, 1 Oct 2003 16:29:16 -0700 [thread overview]
Message-ID: <20031001162916.5fc2241b.akpm@osdl.org> (raw)
In-Reply-To: <37940000.1065035945@w-hlinder>
Hanna Linder <hannal@us.ibm.com> wrote:
>
> In mainline, once block size is over 32k our throuput actually drops off.
> It levels off around 128k but at a greater cpu utilization.
> Dont really understand why that is.
Probably thrashing the CPU's L1 cache.
> In mm tree, maintains throughput for all block size but the cpu utilzation
> keeps going up to do the same throughput. Readprofile shows the extra time
> is being spent in copy_to_user (in mm tree). Backing out readahead patch
> reduces cpu by 10% for all block sizes but still shows the spike. So that
> isnt the main problem.
If you have a loop like:
char *buf;
for (lots) {
read(fd, buf, size);
}
the optimum value of `size' is small: as little as 8k. Once `size' gets
close to half the size of the L1 cache you end up pushing the memory at
`buf' out of CPU cache all the time.
next prev parent reply other threads:[~2003-10-01 23:29 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-10-01 19:19 Minutes from 10/1 LSE Call Hanna Linder
2003-10-01 23:29 ` Andrew Morton [this message]
2003-10-01 23:38 ` Larry McVoy
2003-10-02 0:23 ` Jeff Garzik
2003-10-02 18:56 ` insecure
2003-10-02 19:10 ` Jeff Garzik
2003-10-02 22:38 ` insecure
2003-10-02 22:45 ` Hanna Linder
2003-10-05 5:38 ` Andrew Morton
2003-10-02 19:21 ` [Lse-tech] " Steven Pratt
2003-10-02 19:36 ` Andrew Morton
2003-10-03 19:33 ` Steven Pratt
2003-10-03 20:13 ` Andrew Morton
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