linux-kernel - Re: RFC: starting a kernel-testers group for newbies

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Message-ID: <20080509193043.GA22445@beyonder.ift.unesp.br>
Date:	Fri, 9 May 2008 16:30:43 -0300
From:	"Carlos R. Mafra" <crmafra2@...il.com>
To:	Mark Lord <lkml@....ca>
Cc:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Adrian Bunk <bunk@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Josh Boyer <jwboyer@...il.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, davem@...emloft.net,
	linux-kernel@...r.kernel.org, jirislaby@...il.com,
	Steven Rostedt <rostedt@...dmis.org>, tglx@...utronix.de,
	Len Brown <lenb@...nel.org>
Subject: Re: RFC: starting a kernel-testers group for newbies

On Fri  9.May'08 at 12:32:51 -0400, Mark Lord wrote:
> Pallipadi, Venkatesh wrote:
>>  
>>> -----Original Message-----
>>> From: linux-kernel-owner@...r.kernel.org 
>>> [mailto:linux-kernel-owner@...r.kernel.org] On Behalf Of Carlos R. Mafra
>>> Sent: Friday, May 02, 2008 10:16 AM
>>> To: Linus Torvalds
>>> Cc: Adrian Bunk; Paul Mackerras; Josh Boyer; Arjan van de Ven; Andrew 
>>> Morton; Rafael J. Wysocki; davem@...emloft.net; 
>>> linux-kernel@...r.kernel.org; jirislaby@...il.com; Steven Rostedt; 
>>> Pallipadi, Venkatesh
>>> Subject: Re: RFC: starting a kernel-testers group for newbies
>>>
>>> On Fri  2.May'08 at  9:28:08 -0700, Linus Torvalds wrote:
>>>
>>>> Quite frankly, it does sound like the hang happens somewhere 
>>> around the 
>>>> 	hpet_init
>>>> 	hpet_acpi_add
>>>> 	hpet_resources
>>>> 	hpet_resources: 0xfed00000 is busy
>>>>
>>>> printk's you added (correct?) and we've had tons of issues 
>>> with NO_HZ, so 
>>>> at a guess it is timer-related.
>>> It happens a bit before that because when it hangs it doesn't print the 
>>> above lines, and when it does not hang these lines are
>>> the ones right after the point where it hangs. 
>>>> (And I assume it's stable if/once it gets past that boot hang issue? 
>>> Yes you are right. When I have luck and the boot succeeds my Sony laptop
>>> is rock solid and the kernel is wonderful (even the card reader works!).
>>>
>>>> That
>>>> tends to mean that it's not some hardware instability, it's 
>>> literally our 
>>>> init code).
>>> A few days ago I found this message in lkml in reply to a hpet patch
>>> http://lkml.org/lkml/2007/5/7/361 in which the reporter also had a 
>>> similar hang, which was cured by hpet=disable. 
>>> So it is in my TODO list to try to check out if that patch is in the 
>>> current -git and whether it can be reverted somehow (I added Venki to the 
>>> Cc: now)
>>>
>>> Thanks a lot for the answer!
>>
>> It depends on whether we are HPET is being force detected based on the
>> chipset or whether it was exported by the BIOS in ACPI table.
>>
>> If it was force enabled and above patch is having any effect, then you
>> should see a message like
>>> Force enabled HPET at base address 0xfed00000
>>
>> In any case, off late there seems to be quite a few breakages that are
>> related to HPET/timer interrupts. One of them was on a system which has
>> HPET being exported by BIOS
>> http://bugzilla.kernel.org/show_bug.cgi?id=10409
>> And the other one where we are force enabling based on chipset
>> http://bugzilla.kernel.org/show_bug.cgi?id=10561
>>
>> And then we have hangs once in a while reports by you, Roman and Mark
>> here
>> http://bugzilla.kernel.org/show_bug.cgi?id=10377
>> http://bugzilla.kernel.org/show_bug.cgi?id=10117
> ..
>
> Yeah.  This particular bug first appeared when NOHZ & HPET were added.
> Somebody once suggested it had something to do with an SMI interrupt
> happening in the midst of HPET calibration or some such thing.
>

I said I was waiting for -rc1 to be released to send another email
about my HPET problem, but curiously with v2.6.26-rc1-6-gafa26be 
my laptop did not hang after 30+ boots and counting. 

Somewhere between 2.6.25-07000-(something) and the above kernel
something happened which changed significantly the probability
of hanging during boot. 

I could not boot more than 3 times in
a row without hanging with kernels up to 2.6.25-07000 (approximately),
and now I am still booting v2.6.26-rc1-6-gafa26be a few times a day
and no hangs yet.

Yesterday I started a "reverse" bisection, trying to find which
commit "fixed" it, but I still didn't finish (but it is past
-7200).

Of course I am not sure if after the 100th boot the latest -git
won't hang but it definitely improved.

> But nobody who works on the HPET code has ever shown more than a casual
> interest in helping to track down and fix whatever the problem is.

Well, I would like to thank Venki for his effort because he even
answered some private emails from me about this issue and is 
tracking the bugzillas about it.
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