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From: Jesse Barnes <jbarnes@engr.sgi.com>
To: Andrew Morton <akpm@osdl.org>
Cc: linux-kernel@vger.kernel.org, jeremy@sgi.com
Subject: Re: Buffered I/O slowness
Date: Mon, 1 Nov 2004 10:26:34 -0800	[thread overview]
Message-ID: <200411011026.34102.jbarnes@engr.sgi.com> (raw)
In-Reply-To: <20041029173045.32722ac0.akpm@osdl.org>

On Friday, October 29, 2004 5:30 pm, Andrew Morton wrote:
> Jesse Barnes <jbarnes@engr.sgi.com> wrote:
> > > I'm not sure that we know what's going on yet.  I certainly don't.  The
> > > above numbers look good, so what's the problem???
> >
> > The numbers are ~1/3 of what the machine is capable of with direct I/O.
>
> Are there CPU cycles to spare?  If you have just one CPU copying 1GB/sec
> out of pagecache, maybe it is pegged?

Hm, I thought I had more CPU to spare, but when I set the readahead to a large 
value, I'm taking ~100% of the CPU time on the CPU doing the read.  ~98% of 
that is system time.  When I run 8 copies (this is an 8 CPU system), I get 
~4GB/s and all the CPUs are near fully busy.  I guess things aren't as bad as 
I initially thought.

Thanks,
Jesse

  reply	other threads:[~2004-11-01 18:47 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2004-10-26  1:14 Buffered write slowness Jesse Barnes
2004-10-29 17:46 ` Buffered I/O slowness Jesse Barnes
2004-10-29 23:08   ` Andrew Morton
2004-10-30  0:16     ` Jesse Barnes
2004-10-30  0:30       ` Andrew Morton
2004-11-01 18:26         ` Jesse Barnes [this message]
2004-11-01 18:34           ` Jesse Barnes

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