linux-kernel - Re: [patch 00/22] high resolution timers / dynamic ticks

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Date:	05 Oct 2006 22:57:24 +0200
From:	Andi Kleen <ak@...e.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	John Stultz <johnstul@...ibm.com>,
	Valdis Kletnieks <valdis.kletnieks@...edu>,
	Arjan van de Ven <arjan@...radead.org>,
	Dave Jones <davej@...hat.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Jim Gettys <jg@...top.org>,
	Roman Zippel <zippel@...ux-m68k.org>, akpm@...l.org
Subject: Re: [patch 00/22] high resolution timers / dynamic ticks - V3

Ingo Molnar <mingo@...e.hu> writes:

> * Andrew Morton <akpm@...l.org> wrote:
> 
> > With CONFIG_HIGH_RES_TIMERS=y, CONFIG_NO_HZ=n it's pretty sick.  It 
> > pauses for several seconds after "input: AlpsPS/2 ALPS GlidePoint as 
> > /class/input/input2" (printk-time claims 2 seconds, but it was longer 
> > than that).
> > 
> > It's been stuck for a minute or more at the 12.980000 time, seems to 
> > have hung.  The cursor is flashing extremely slowly.
> 
> ah, that's still the VAIO, right? Do you get a 'slow' LOC count on 
> /proc/interrupts even on a stock kernel? If yes then that's a 
> fundamentally sick local APIC timer interrupt. Stock kernel should show 
> sickness too, if for example you boot an SMP kernel on it - can you 
> confirm that? (the UP-IOAPIC only relies for profiling on the lapic 
> timer, so there the only sickness you should see on the stock kernel is 
> a non-working readprofile)

When I was hacking on my old noidletick patch I ran into this
problem on several machines too.

But usually the problem wasn't that it was too slow, but that
it completely stopped in C2 or deeper. I don't think there
is a way to work around that except for not using C2 or deeper
(not an option) or using a different timer source.

If that is true then hitting space lots of time will make it 
go faster.

-andi
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