linux-kernel - Re: Remove constructor from buffer

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Message-Id: <20070504134212.c18d2d65.akpm@linux-foundation.org>
Date:	Fri, 4 May 2007 13:42:12 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Christoph Lameter <clameter@....com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Remove constructor from buffer_head

On Thu, 3 May 2007 20:08:41 -0700 (PDT)
Christoph Lameter <clameter@....com> wrote:

> Performance tests show a slight improvements in netperf (not a
> strong case for a performance improvement but removing the
> constructor has definitely no negative impact so why keep
> this around?).
> 
> TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to localhost (127.0.0.1) port 0 AF_INET
> Recv   Send    Send
> Socket Socket  Message  Elapsed
> Size   Size    Size     Time     Throughput
> bytes  bytes   bytes    secs.    10^6bits/sec
> 
> Before:
>  87380  16384  16384    10.01    6026.04
>  87380  16384  16384    10.01    5992.17
>  87380  16384  16384    10.01    6071.23
> 
> After:
>  87380  16384  16384    10.01    6090.20
>  87380  16384  16384    10.01    6078.3
>  87380  16384  16384    10.00    6013.52
> 
> 
> Signed-off-by: Christoph Lameter <clameter@....com>
> 
> ---
>  fs/buffer.c |   22 ++++------------------


So I benchmarked this by repeatedly extending (via write()) and truncating
a 10MB file, on ext2.  Using create-delete.c from
http://www.zip.com.au/~akpm/linux/patches/stuff/ext3-tools.tar.gz

Machine is a fast 2x4 core Woodcrest.  CONFIG_SLAB=y

The command used was

	time create-delete -s $((16 * 1024 * 1024)) -n 300 foo

which will allocate and free 300*4096 buffer_heads.

With patch:

akpm2:/mnt/sda2> time create-delete -s $((16 * 1024 * 1024)) -n 300 foo
create-delete -s $((16 * 1024 * 1024)) -n 300 foo  0.00s user 4.56s system 99% cpu 4.565 total
akpm2:/mnt/sda2> time create-delete -s $((16 * 1024 * 1024)) -n 300 foo
create-delete -s $((16 * 1024 * 1024)) -n 300 foo  0.00s user 4.60s system 99% cpu 4.612 total
akpm2:/mnt/sda2> time create-delete -s $((16 * 1024 * 1024)) -n 300 foo
create-delete -s $((16 * 1024 * 1024)) -n 300 foo  0.00s user 4.60s system 99% cpu 4.602 total
akpm2:/mnt/sda2> time create-delete -s $((16 * 1024 * 1024)) -n 300 foo
create-delete -s $((16 * 1024 * 1024)) -n 300 foo  0.00s user 4.56s system 99% cpu 4.567 total
akpm2:/mnt/sda2> time create-delete -s $((16 * 1024 * 1024)) -n 300 foo
create-delete -s $((16 * 1024 * 1024)) -n 300 foo  0.00s user 4.59s system 95% cpu 4.824 total

Without patch:

akpm2:/mnt/sda2> time create-delete -s $((16 * 1024 * 1024)) -n 300 foo
create-delete -s $((16 * 1024 * 1024)) -n 300 foo  0.00s user 4.42s system 99% cpu 4.419 total
akpm2:/mnt/sda2> time create-delete -s $((16 * 1024 * 1024)) -n 300 foo
create-delete -s $((16 * 1024 * 1024)) -n 300 foo  0.00s user 4.42s system 99% cpu 4.421 total
akpm2:/mnt/sda2> time create-delete -s $((16 * 1024 * 1024)) -n 300 foo
create-delete -s $((16 * 1024 * 1024)) -n 300 foo  0.00s user 4.42s system 99% cpu 4.427 total
akpm2:/mnt/sda2> time create-delete -s $((16 * 1024 * 1024)) -n 300 foo
create-delete -s $((16 * 1024 * 1024)) -n 300 foo  0.00s user 4.42s system 99% cpu 4.417 total
akpm2:/mnt/sda2> time create-delete -s $((16 * 1024 * 1024)) -n 300 foo
create-delete -s $((16 * 1024 * 1024)) -n 300 foo  0.00s user 4.42s system 99% cpu 4.435 total

So the patch took the average system time from 4.42 seconds up to 4.582
seconds.  Nice slowdown!

It could just be the usual inter-kernel-build noise, dunno.

I'd investigate further, but someone has gone and broken oprofile.

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