linux-kernel - [FALSE ALARM] Re: HPET (?) related hangs and breakage in 2.6.35,36

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Date:	Wed, 10 Nov 2010 13:48:00 -0500
From:	Andrew Lutomirski <luto@....edu>
To:	Borislav Petkov <bp@...64.org>
Cc:	Clemens Ladisch <clemens@...isch.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	x86 <x86@...nel.org>
Subject: [FALSE ALARM] Re: HPET (?) related hangs and breakage in 2.6.35,36

On Tue, Nov 9, 2010 at 4:29 PM, Andrew Lutomirski <luto@....edu> wrote:
> On Tue, Nov 9, 2010 at 1:01 PM, Borislav Petkov <bp@...64.org> wrote:
>> On Tue, Nov 09, 2010 at 12:44:48PM -0500, Andrew Lutomirski wrote:
>>> I may have just reproduced after a couple of days of uptime it in
>>> 2.6.36 with hpet=disable (in any case, the system hung and netconsole
>>> didn't work).
>>>
>>> I'm currently testing the hpet_min_tick stuff, backported to 2.6.36,
>>> with hpet on.  Haven't had a problem yet, but I'll see what happens
>>> after a few hours.  So far, it said:
>>>
>>> ACPI: HPET id: 0x8086a301 base: 0xfed00000 min tick: 128
>>
>> This doesn't say what your BIOS has set it to originally. For that, do
>>
>> hexdump -C /sys/firmware/acpi/tables/HPET
>>
>> and check what does the u16 little endian value at offset 0x35 say.
>
> 0x37ee, which people have seen before.  In any case, even with the
> patch applied my system hung, and I still got this off netconsole
> sometime around when the hang happened:
>
> Clocksource: tsc unstable (delta = -34355296774 ns)
> Switching: to clocksource hpet

Please disregard -- this is a bug in nouveau (or drm) not hpet.  I'll
send a bug report to the maintainers.

--Andy

>
> Another odd symptom: none of the SysRq hotkeys I could think of did
> anything *except for SysRq-b*.  I have no idea what could cause that.
>
> My system appears to pass ingo's time-warp-test (when compiled with
> -O0 -- it segfaults with -O2), so I think my TSC is okay.
>
> --Andy
>
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