linux-kernel - Re: Remove constructor from buffer

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Message-Id: <20070503213717.37be3e56.akpm@linux-foundation.org>
Date:	Thu, 3 May 2007 21:37:17 -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 20:34:48 -0700 (PDT) Christoph Lameter <clameter@....com> wrote:

> On Thu, 3 May 2007, Andrew Morton wrote:
> 
> > 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
> > 
> > How could a filesystem change affect networking performance?
> > 
> > The change looks nice, but I'd microbenchmark it with a write-to-ext2-on-ramdisk
> > or something like that.
> 
> Hmmmm.. I was told in another thread that this is the most frequently used 
> slab for this benchmark

That would be hair-raising ;)  I suspect confusion with sk_buff.

buffer_heads do get used quite a bit though.  A good microbenchmark would
be to sit in a tight loop extending and truncating an ext2 file

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