linux-kernel - Re: PMTMR running too fast

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Date:	Tue, 05 Dec 2006 07:41:38 +0000
From:	Ian Campbell <ijc@...lion.org.uk>
To:	john stultz <johnstul@...ibm.com>
Cc:	linux-kernel@...r.kernel.org, Andi Kleen <ak@...e.de>
Subject: Re: PMTMR running too fast

On Mon, 2006-12-04 at 12:14 -0800, john stultz wrote:
> On Mon, 2006-12-04 at 19:40 +0000, Ian Campbell wrote:
> > On Mon, 2006-12-04 at 11:19 -0800, john stultz wrote:
> > > On Sun, 2006-12-03 at 13:50 +0000, Ian Campbell wrote:
> > > > In older kernels arch/i386/kernel/timers/timer_pm.c:verify_pmtmr_rate
> > > > contained a check for sensible PMTMR rate and disabled that clocksource
> > > > if it was found to be out of spec[0]. This check seems to have been lost
> > > > in the transition to drivers/clocksource/acpi_pm.c, the removal is in
> > > > 61743fe445213b87fb55a389c8d073785323ca3e "Time: i386 Conversion - part
> > > > 4: Remove Old timer_opts Code"[1] and the check is not present in the
> > > > replacement 5d0cf410e94b1f1ff852c3f210d22cc6c5a27ffa "Time: i386
> > > > Clocksource Drivers"[2].
> > > 
> > > Fedora has a bug covering this:
> > > https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=211902
> > 
> > > > Is there a specific reason the check was removed (I couldn't see on in
> > > > the archives) or was it simply overlooked? Without it I need to pass
> > > > clocksource=tsc to have 2.6.18 work correctly on an older K6 system with
> > > > an Aladdin chipset (will dig out the precise details if required). Would
> > > > a patch to reintroduce the check be acceptable or would some sort of
> > > > blacklist based solution be more acceptable?
> > > 
> > > If I recall correctly, it was pulled because there was some question as
> > > to if it was actually needed (x86_64 didn't need it) and it slows down
> > > the boot time (although not by much). 
> > > 
> > > I'm fine just re-adding it. Although if the number of affected systems
> > > are small we could just blacklist it (Ian, mind sending dmidecode
> > > output?).
> 
> I don't have a dev box to test on at the moment, but here's a quick hack
> attempt at re-adding the code. Does the following work for you? 

I get:
        PM-Timer running at invalid rate: 200% of normal - aborting.
        ...
        Time: pit clocksource has been installed.
        
Without the clocksource parameter.

Should tsc be preferred to pit though?

/sys/devices/system/clocksource/clocksource0/available_clocksource now
shows "jiffies tsc pit" and current_clocksource is "pit".

Thanks,
Ian.

-- 
Ian Campbell

love, n.:
	When it's growing, you don't mind watering it with a few tears.

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