linux-kernel - Re: [PATCH 0/2] fix the itimer regression (BZ 12618)

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Message-ID: <20090212110500.GB23665@elte.hu>
Date:	Thu, 12 Feb 2009 12:05:00 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Lin Ming <ming.m.lin@...el.com>,
	Mike Galbraith <efault@....de>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"oleg@...hat.com" <oleg@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"seto.hidetoshi@...fujitsu.com" <seto.hidetoshi@...fujitsu.com>
Subject: Re: [PATCH 0/2] fix the itimer regression (BZ 12618)


* Zhang, Yanmin <yanmin_zhang@...ux.intel.com> wrote:

> On Tue, 2009-02-10 at 13:47 +0100, Peter Zijlstra wrote:
> > On Mon, 2009-02-09 at 22:47 +0100, Ingo Molnar wrote:
> > > * Lin Ming <ming.m.lin@...el.com> wrote:
> > > 
> > > > On Fri, 2009-02-06 at 23:18 +0800, Ingo Molnar wrote:
> > > > > * Zhang, Yanmin <yanmin_zhang@...ux.intel.com> wrote:
> > > > > 
> > > > > > On Thu, 2009-02-05 at 13:06 +0100, Ingo Molnar wrote:
> > > > > > > * Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> > > > > > > 
> > > > > > > > This should hopefully address all the itimer borkage.
> > > > > > > 
> > > > > > > Applied to tip:timers/urgent, thanks Peter!
> > > > > > > 
> > > > > > > Yanmin: could you check hacbench_pth with latest tip/master, do
> > > > > > > these fixes resolve that 3% regression you reported?
> > > > > >
> > > > > > Lin Ming tested it and hackbench_pth/volanoMark regression all disappear. 
> > > > > > But oltp has a regression. We think oltp new regression isn't related to 
> > > > > > the patch. Ming is investigating it.
> > > > > 
> > > > > Potential suspects for oltp regression would be:
> > > > > 
> > > > >  3d39870: sched_rt: don't use first_cpu on cpumask created with cpumask_and
> > > > >  a571bbe: sched: fix buddie group latency
> > > > >  a9f3e2b: sched: clear buddies more aggressively
> > > > >  1596e29: sched: symmetric sync vs avg_overlap
> > > > >  d942fb6: sched: fix sync wakeups
> > > > 
> > > > I tested the latest tip-master branch.
> > > > After reverting "d942fb6: sched: fix sync wakeups", the oltp regression
> > > > on the 8cores Stockley machine is mostly fixed.
> > > > 
> > > > On another 4*4 cores Tigerton machine, oltp has more than 10% regression
> > > > with 2.6.29-rc4 compared with 2.6.29-rc3.
> > > 
> > > ok, that commit needs fixed or reverted. Peter, Mike?
> > 
> > Yanmin, is that tigerton regression also due to the sync changes?
> Yes.
> 
> > 
> > That is, if you revert both d942fb6 and 1596e29, does it get back to
> > -rc3 state,
> Yes.
> 
> >  or is the tigerton regression due to something else?
> > This isn't quite clear to me.
> > 
> > Ingo, if that is the case, I'm fine with reverting those changes for
> > now, and have another look at them later on -- preferably when someone
> > ships me a 4*4 machine so I can validate :-)
> 2*4 stoakley has the similiar regression. To find potential scalability issues,
> I run sysbench+mysql(oltp) with many thread numbers, such like 8,12,16,32,64,128,
> then get an average value.

FYI, in Linus's latest tree (v2.6.29-rc4-175-gb578f3f or later), all
the scheduler related performance regressions should be addressed.

Could you please double-check that there's no performance regression
remaining?

Thanks,

	Ingo
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