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

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> On 16.08.11 at 11:47, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> We have had a bug raised against Xen-3.4 that the kexec path fails, on
> HP BL465c G7 blades.  The problem does not reproduce on any other AMD
> machines I have to hand.
> 
> On further investigation, it appears that if the crashing cpu is #0,
> then the kexec path hangs forever trying to grab the already locked
> legacy_hpet_event.lock in hpet_disable_legacy_broadcast().  Removing the
> lock/unlock pair causes the kexec crash path to work as expected.

Are you sure it is locked (rather than never initialized)? The problem
could be that hpet_broadcast_is_available() returns true because of
num_hpets_used > 0, yet hpet_broadcast_init() didn't make it down
to spin_lock_init(&legacy_hpet_event.lock).

> If the crashing cpu is not #0, then local_time_calibration() gets
> worried and dumps the calibration data, and hangs at some later point
> which I have yet to find.  This hang happens while performing the NMI
> shootdown of other cpus.
> 
> 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.

Jan


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