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[Xen-devel] RE: How to generate a HW NMI

Until Friday, all hard hangs that we and our customers had experienced
were on Lenovo T500 and X200, even with their latest BIOSes.  The Lenovo
T400 has never hung for me and I don't have any reports on them from the
field.  On Friday, I had an HP i5 hard hang with similar footprint as
the Lenovos.  When this hard hang happens, the Xen watchdog (which is
driven by the NMI handler) will not do its job and cause a crash/stack
trace.  This is why we have started to suspect something with the BIOS
and SMIs as they are the only thing that can block an NMI.  I am pretty
certain that this is somehow related to entering C3 power states and
possibly at the same time an SMI comes in.  The time it takes to hang
varies from 30mins to 24 hrs.


-----Original Message-----
From: Jan Kiszka [mailto:jan.kiszka@xxxxxxxxxxx] 
Sent: Monday, October 04, 2010 10:13 AM
To: Roger Cruz
Cc: Konrad Rzeszutek Wilk; xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: How to generate a HW NMI

Am 04.10.2010 15:56, Roger Cruz wrote:
> Jan,
> I will try your suggestion of turning off SMIs. I am also interested
in you 
> conducting an experiment for me. If you can, please tell your kernel
not to use 
> any CPU power saving modes. In Xen I use max_cstate=0 in the bootline.
I have 
> found that when I do this, the hangs appear to go away (we had one
> report one since using this work-around, so it is not 100% working).

Will do. My customer reported that he was able to easily crash his i7
notebook by pulling and re-plugging the power cable. I bet all of these
events are trapped by the BIOS via power management SMIs...

BTW, do you see any correlation between crashable boxes and BIOS
vendors? We have no representative numbers yet, just one confirmed
instable notebook that is Phoenix-based, while one AMI-based i7 server
that is rock-stable.


Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux

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