linux-kernel - Re: [BISECTED] 2.6.35.*: horrible (exponential? >linear) slowdown to unusability (HPET)

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Date:	Tue, 14 Sep 2010 12:09:57 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Nix <nix@...eri.org.uk>
cc:	Artur Skawina <art.08.09@...il.com>,
	Venkatesh Pallipadi <venki@...gle.com>,
	Damien Wyart <damien.wyart@...e.fr>,
	John Drescher <drescherjm@...il.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [BISECTED] 2.6.35.*: horrible (exponential? >linear) slowdown
 to unusability (HPET)

On Fri, 10 Sep 2010, Thomas Gleixner wrote:
> On Fri, 10 Sep 2010, Nix wrote:
> > 
> > I suspect current_clocksource doesn't do what we think it does, or the
> > clocksource and 'clock event device' are not the same.)
> 
> Right, they are not the same. clocksource provides us a read out
> device for timekeeping (usually a simple increasing counter). clock
> event device is used to generate timer interrupts.
> 
> HPET provides both functionalities.
> 
> The patch you bisected is affecting the clock events part of the
> HPET. So yes, it's not a clock source problem.

Another question. If you add hpet=verbose (or revert that commit) does
the printk_once in hpet_set_next_event() show up in dmesg ?

    "hpet: compare register read back failed."

Thanks,

	tglx
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