Re: Direct io on block device has performance regression on 2.6.xkernel

From: Andrew Morton
Date: Wed Mar 09 2005 - 15:14:56 EST

"Chen, Kenneth W" <kenneth.w.chen@xxxxxxxxx> 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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