linux-kernel - Re: [URGENT rfc patch 0/3] tsc clocksource bug fix

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Date:	Thu, 4 Jul 2013 22:27:19 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Davidlohr Bueso <davidlohr.bueso@...com>
cc:	Alex Shi <alex.shi@...el.com>, hpa@...ux.intel.com,
	tim.c.chen@...ux.intel.com, linux-kernel@...r.kernel.org,
	andi.kleen@...el.com, a.p.zijlstra@...llo.nl, mingo@...e.hu
Subject: Re: [URGENT rfc patch 0/3] tsc clocksource bug fix

On Thu, 4 Jul 2013, Davidlohr Bueso wrote:

> On Thu, 2013-07-04 at 13:00 +0200, Thomas Gleixner wrote:
> > On Thu, 4 Jul 2013, Alex Shi wrote:
> > 
> > > We find some benchmarks drop a lot on tip/sched/core on many Intel boxes,
> > > like oltp, tbench, hackbench etc. and bisected the commit 5d33b883ae
> > > cause this regression. Due to this commit, the clocksource was changed
> > > to hpet from tsc even tsc will be set CLOCK_SOURCE_VALID_FOR_HRES later
> > > in clocksource_watchdog. 
> > 
> > 5d33b883ae is not in tip/sched/core. So what are you testing and
> > bisecting?
> 
> I think he's referring to:
> 
> commit 5d33b883aed81c6fbcd09c6f7c3619eee850a7e2

I know what he is referring to. He explicitly mentions this commit:

> > > like oltp, tbench, hackbench etc. and bisected the commit 5d33b883ae

What I was pointing out that he was referring to tip sched/core at the
same time

> > > We find some benchmarks drop a lot on tip/sched/core on many Intel boxes,

And that branch does NOT have that commit included. So how can you see
a regression on a branch caused by a commit NOT included into that
branch?

The offending commit is in tip timers/core and not in tip
sched/core. What I'm wanted to say is, that we need a proper
description of problems and not some random association.

It tricked you to assume, that I'm not able to figure it out myself :)

See? These things are complex and subtle, so we need precise
descriptions and not some sloppy semi correct data.

I'm well aware of the issue and with Peters help I got a reasonable
explanation for it. A proper fix is about to be sent out.

Thanks,

	tglx
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