linux-kernel - Re: [BUG] jiffies counter leaps in 2.6.24-rc3

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Message-ID: <20071129174548.GC12481@redhat.com>
Date:	Thu, 29 Nov 2007 12:45:48 -0500
From:	Dave Jones <davej@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Stefano Brivio <stefano.brivio@...imi.it>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org,
	Michael Buesch <mb@...sch.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Len Brown <lenb@...nel.org>
Subject: Re: [BUG] jiffies counter leaps in 2.6.24-rc3

On Thu, Nov 29, 2007 at 11:35:11AM +0100, Ingo Molnar wrote:
 
 > * Stefano Brivio <stefano.brivio@...imi.it> wrote:
 > 
 > > Ok, I found out how to reliably reproduce this bug. The root session issue
 > > was a bit weird, but I noticed I usually switch to root only when I need to
 > > change the CPU frequency. And here's what happens:
 > > 
 > > # cpuspeedy min
 > > [after some time...]
 > > Nov 29 09:42:31 morte [ 4408.722597] b43-phy0 ERROR: PHY transmission error
 > > 
 > > # cpuspeedy max
 > > Nov 29 09:42:41 morte [ 1177.238599] wmaster0: STA 00:14:c1:35:8d:eb Average rate: 540 (2160/4)
 > > 
 > > It looks like jiffies get scaled exactly by a 3.75 factor, which is
 > > <max_frequency>/<min_frequency> here. I use acpi-cpufreq and this is my
 > 
 > ah, the cpufreq/acpi/acpi-cpufreq angle is indeed a big clue. I've 
 > Cc:-ed various interested parties.
 
Hmm, what's in /sys/devices/system/clocksource/clocksource0/current_clocksource  ?

adjust_jiffies() always gets called on a speed transition. I'm wondering
if perhaps we shouldn't do that if we're using something other than
the tsc for timekeeping.

	Dave

-- 
http://www.codemonkey.org.uk
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