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

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Message-ID: <4CBEB8A3.6080100@suse.cz>
Date:	Wed, 20 Oct 2010 11:38:43 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	unlisted-recipients:; (no To-header on input)
CC:	Thomas Gleixner <tglx@...utronix.de>,
	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 10/12/2010 12:02 AM, Jiri Slaby wrote:
> 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/

Did anybody have a chance to look into the logs? Should I create a bug
at kernel.org for that? Or provide more info?

thanks,
-- 
js
suse labs
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