linux-kernel - Re: [PATCH 3/5] lockstat: core infrastructure

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Date:	Fri, 01 Jun 2007 08:26:46 -0700
From:	Daniel Walker <dwalker@...sta.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jason Baron <jbaron@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 3/5] lockstat: core infrastructure

On Fri, 2007-06-01 at 15:12 +0200, Ingo Molnar wrote:
> * Daniel Walker <dwalker@...sta.com> wrote:
> 
> > On Wed, 2007-05-30 at 19:16 +0200, Peter Zijlstra wrote:
> 
> > > I think you are mistaken here; the two are similar but not 
> > > identical.
> > > 
> > > I see sched_clock() as fast first, accurate second. Whereas the 
> > > clocksource thing is accurate first, fast second.
> > 
> > This is true .. However, if there is a speed different it's small.
> 
> Ugh. Have you ever compared pmtimer (or even hpet) against TSC based 
> sched_clock()? What you write is so wrong that it's not even funny. You 
> keep repeating this nonsense despite having been told multiple times 
> that you are dead wrong.

Yes I have, and your right there is a difference, and a big
difference .. Above I was referring only to the TSC clocksource, since
that's an apples to apples comparison .. I would never compare the TSC
to the acpi_pm, that's no contest ..

The acpi_pm as sched_clock() with hackbench was about %25 slower, the
pit was 10x slower approximately. (I did this months ago.)

Daniel

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