Date: Wed, 9 Mar 2005 12:04:58 -0800
From: Andrew Morton <akpm@osdl.org>
To: "Chen, Kenneth W" <kenneth.w.chen@intel.com>
Cc: linux-kernel@vger.kernel.org, axboe@suse.de
Subject: Re: Direct io on block device has performance regression on 2.6.x
 kernel
Message-Id: <20050309120458.7c25f5e3.akpm@osdl.org>
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References: <20050308222737.3712611b.akpm@osdl.org>
	<200503091721.j29HLNg24054@unix-os.sc.intel.com>
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"Chen, Kenneth W" <kenneth.w.chen@intel.com> wrote:
>
> Andrew Morton wrote on Tuesday, March 08, 2005 10:28 PM
> > But before doing anything else, please bench this on real hardware,
> > see if it is worth pursuing.
> 
> Let me answer the questions in reverse order.  We started with running
> industry standard transaction processing database benchmark on 2.6 kernel,
> on real hardware (4P smp, 64 GB memory, 450 disks) running industry
> standard db application.  What we measured is that with best tuning done
> to the system, 2.6 kernel has a huge performance regression relative to
> its predecessor 2.4 kernel (a kernel from RHEL3, 2.4.21 based).

That's news to me.  I thought we were doing OK with big database stuff. 
Surely lots of people have been testing such things.

> And yes, it is all worth pursuing, the two patches on raw device recuperate
> 1/3 of the total benchmark performance regression.

On a real disk driver?  hm, I'm wrong then.

Did you generate a kernel profile?

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