linux-kernel - Re: HPET causes tasks to freeze (still in 2.6.36-rc6)

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Date:	Tue, 12 Oct 2010 00:02:08 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	LKML <linux-kernel@...r.kernel.org>, clemens@...isch.de,
	venki@...gle.com, the arch/x86 maintainers <x86@...nel.org>
Subject: Re: HPET causes tasks to freeze (still in 2.6.36-rc6)

On 10/04/2010 06:31 PM, Thomas Gleixner wrote:
> On Mon, 4 Oct 2010, Jiri Slaby wrote:
>> HPET as a clocksource has still issues in the latest kernels (confirmed
>> in 2.6.36-rc6) at least on x86_64. Unless clocksource=jiffies,
>> clocksource=tsc or nolapic_timer is used, the system is unusable. Tasks
>> are not woken unless mouse is moved, key is pressed (or other hard irq
>> triggered). 2.6.32 seems to be the last working.
> 
> The problem is not clocksource related, it's NOHZ related.
> 
> clocksource=jiffies, clocksource=tsc are disabling NOHZ simply because
> we can not do NOHZ neither with jiffies nor with a TSC which stops in
> deeper C-states.
> 
> nolapic_timer installs a dummy lapic timer so the lapic is not used,
> but HPET is used instead and NOHZ is disabled as well.
> 
> So the real problem is that the hpet broadcast interrupts which are
> used to work around the lapic timer stops in C3 problem are not coming
> through for whatever reason.
> 
> So the question is what changed in the ACPI/idle NOHZ code which might
> expose this problem.
> 
> Can we get dmesg, output of proc/timer_list and output of
> /proc/acpi/processor/CPU0/power for a .32 and a non working kernel
> please ?

Sure:
http://labs.suse.cz/jslaby/bug-579932/

thanks,
-- 
js
suse labs
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