linux-kernel - Re: various laptop nagles - any suggestions? (note: 2.6.19-rc2-mm1 but applies to multiple kernels)

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Message-Id: <1161424147.5274.400.camel@localhost.localdomain>
Date:	Sat, 21 Oct 2006 11:49:07 +0200
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andrew Morton <akpm@...l.org>
Cc:	Ingo Molnar <mingo@...e.hu>, teunis <teunis@...tersgift.com>,
	linux-kernel@...r.kernel.org, Dmitry Torokhov <dtor@...l.ru>,
	john stultz <johnstul@...ibm.com>
Subject: Re: various laptop nagles - any suggestions?   (note:
	2.6.19-rc2-mm1 but applies to multiple kernels)

On Fri, 2006-10-20 at 18:25 -0700, Andrew Morton wrote:
> On Fri, 20 Oct 2006 22:56:51 +0200
> Ingo Molnar <mingo@...e.hu> wrote:
> 
> > 
> > * Andrew Morton <akpm@...l.org> wrote:
> > 
> > > Oh.  I thought the problem was that the timer stops when the CPU is 
> > > idle. Maybe I misremembered.  I'll try `idle=poll'.
> > 
> > hm, wouldnt in that case the box not boot at all? But yeah, idle=poll 
> > would be nice.
> 
> idle=poll fixes it.  The fan gets a bit noisy though ;)

So this is one of the boxen where C2 is actually C3 and lapic stops in
C3 mode. Probably BIOS magic.

What's the output of /proc/acpi/processor/CPU0/power ?

> Perhaps a suitable test would be to set up a PIT interrupt, do a hlt, see
> if the APIC timer counter has increased appropriately.

Yeah, but it has to be done later in the boot process. Looking into this
right now.

> I got this:
> 
> [   43.709238] TSC appears to be running slowly. Marking it as unstable
> 
> How come?  It also happens with HIGH_RES_TIMERS=n and NO_HZ=n.  It only
> seems to happen when idle=poll is given.

Should happen always as the TSC is driven by the CPU clock and you have
CPUFREQ enabled.

> > could you also boot with apic=verbose and send us the full bootlog?
>
> http://userweb.kernel.org/~akpm/apic.txt

[   11.515305] calibrating APIC timer ...
[   11.618612] ..... tt1-tt2 831283
[   11.618614] ..... mult: 35701101
[   11.618616] ..... calibration result: 532021
[   11.618619] ..... CPU clock speed is 1995.0325 MHz.
[   11.618622] ..... host bus clock speed is 133.0021 MHz.

That looks reasonable. It really boils down to the lapic not working
when going idle.

	tglx


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