linux-kernel - Re: [patch 00/21] high resolution timers / dynamic ticks

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Date:	Mon, 02 Oct 2006 11:38:36 -0700
From:	john stultz <johnstul@...ibm.com>
To:	Valdis.Kletnieks@...edu
Cc:	tglx@...utronix.de, Andrew Morton <akpm@...l.org>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Jim Gettys <jg@...top.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: [patch 00/21] high resolution timers / dynamic ticks - V2

On Mon, 2006-10-02 at 14:25 -0400, Valdis.Kletnieks@...edu wrote:
> (Sorry for the size of the note, there's some 50K of logs attached)
>
> On Mon, 02 Oct 2006 15:43:02 +0200, Thomas Gleixner said:
> > Can you please send me the bootlog and further dmesg output (especially
> > when related to timers / cpufreq).
> 
> I booted the box to single-user both times, and then started cpuspeed.
> I then did a cat of /proc/interrupts, /proc/uptime, and a date command,
> waited 60 seconds according to my watch, and repeated.  I then dumped
> the dmesg.  The -dyntick kernel moved 'uptime' almost exactly 45 seconds
> (almost certainly a by-product of running at 1.2Ghz rather than 1.6Ghz).
> Does the dyntick code make any unwritten assumptions about a jiffie or
> bogomips remaining constant?
> 
> Attached - config diff, date and /proc dumps from both -mm2 and -mm2-dyntick,
> and the dmesg's from both boots.
> 
> Yell if you have any other questions/suggestions/etc..

Hmmm. So w/ -mm2 we're seeing the TSC get detected as running too slowly
(and its replaced w/ the ACPI PM), but for some reason that doesn't
happen w/ the dynticks patch.

Now, how is cpuspeed changing the cpufreq? Is it using the /sys
interface? I've got hooks in so when the cpufreq changes we should mark
it unstable and fall back to ACPI PM, but maybe I missed whatever hook
cpuspeed is using.

thanks
-john

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