Re: [Xen-devel] AMD Magny-Cours and HPET

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> On 16.08.11 at 14:32, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> On 16/08/11 11:09, Jan Beulich wrote:
>>>>> On 16.08.11 at 11:47, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>>> The support engineer who raised the bug says that it doesn't occur with
>>> Xen-4.1.  Is there anything architecturally new in the Magny-Cours
>>> processors which might explain this behavior?
>> Possibly more a question of the surrounding platform, namely whether
>> there are HPETs in the system, and whether they get used for the
>> C-state broadcasting.
> 
> Why would C-state broadcasting make a difference at this point?  I have
> narrowed the crash down a bit, and local_time_calibration() is dumping
> its state after one_cpu_only() and before the shootdown actually
> occurs.  However, I cant see any code between these two points which
> alters the state of the other CPU, which should still be running
> normally at this point.

That "num_hpets_used > 0" check in hpet_broadcast_is_available()
could be false for all other AMD systems you had tried this on, and
hence you might not be getting into hpet_disable_legacy_broadcast()
there at all.

(4.0.2 and 4.1.1 have, btw., an extra non-zero check against
legacy_hpet_event.shift in hpet_disable_legacy_broadcast();
4.0.1 and 4.1.0 don't.)

Jan


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