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

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Date:	01 Jun 2007 16:25:47 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Daniel Walker <dwalker@...sta.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bill Huey <billh@...ppy.monkey.org>,
	Jason Baron <jbaron@...hat.com>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH 3/5] lockstat: core infrastructure

Daniel Walker <dwalker@...sta.com> writes:

> On Wed, 2007-05-30 at 19:16 +0200, Peter Zijlstra wrote:
> 
> > > >From the architecture perspective there are two low level clock hooks to
> > > implement one is sched_clock() , and at least one clocksource structure.
> > > Both do essentially the same thing. With timekeepings clocksource
> > > structure actually being easier to implement cause the math is built in.
> > 
> > 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.

pmtimer (factor 1000+) or HPET (factor 10-100+ depending on CPU) 
accesses are much slower than TSC or jiffies read. Talking to the
southbridge is slow.

-Andi
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