linux-kernel - Re: PostgreSQL pgbench performance regression in 2.6.23+

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Date:	Sat, 24 May 2008 01:46:47 +0200
From:	Mike Galbraith <efault@....de>
To:	Greg Smith <gsmith@...gsmith.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Subject: Re: PostgreSQL pgbench performance regression in 2.6.23+


On Fri, 2008-05-23 at 19:18 -0400, Greg Smith wrote:
> On Fri, 23 May 2008, Mike Galbraith wrote:
> 
> > It was running SCHED_BATCH, features=0...it needed features=0 as well to 
> > achieve O(1) batch performance.
> 
> I figured out how to run pgbench with chrt in order to get SCHED_BATCH 
> behavior, but I don't understand what you mean by features=0 here.  Since 
> I didn't see the same magnitude of different just using batch that seems 
> important, where does that get set at?

/proc/sys/kernel/sched_features.  You need CONFIG_SCHED_DEBUG to have
accsess to the scheduler tweakables.

> I'm also curious what hardware your results are coming from, to fit them 
> into my larger pgbench results context space.

A grocery store Q6600 box.

> Got my 4-core system back on-line again today (found some bad RAM) and 
> wanted to try another round of tests on that.  Looks like you've defined 5 
> test sets I should replicate:
> 
> 2.6.22
> 2.6.22, batch
> 2.6.26.git
> 2.6.26.git, batch
> 2.6.26.git, batch + se.load.weight patch
> 
> Should I still be trying Peter's se.waker patch as well in this mix 
> somewhere?

Yeah.

	-Mike

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