Re: Hypervisor crash(!) on xl cpupool-numa-split

[Andre Przywara <andre.przywara@amd.com>]

Andre Przywara wrote:
> On 02/10/2011 07:42 AM, Juergen Gross wrote:
>> On 02/09/11 15:21, Juergen Gross wrote:
>>> Andre, George,
>>>
>>>
>>> What seems to be interesting: I think the problem did always occur when
>>> a new cpupool was created and the first cpu was moved to it.
>>>
>>> I think my previous assumption regarding the master_ticker was not too bad.
>>> I think somehow the master_ticker of the new cpupool is becoming active
>>> before the scheduler is really initialized properly. This could happen, if
>>> enough time is spent between alloc_pdata for the cpu to be moved and the
>>> critical section in schedule_cpu_switch().
>>>
>>> The solution should be to activate the timers only if the scheduler is
>>> ready for them.
>>>
>>> George, do you think the master_ticker should be stopped in suspend_ticker
>>> as well? I still see potential problems for entering deep C-States. I think
>>> I'll prepare a patch which will keep the master_ticker active for the
>>> C-State case and migrate it for the schedule_cpu_switch() case.
>> Okay, here is a patch for this. It ran on my 4-core machine without any
>> problems.
>> Andre, could you give it a try?
> Did, but unfortunately it crashed as always. Tried twice and made sure I 
> booted the right kernel. Sorry.
> The idea with the race between the timer and the state changing sounded 
> very appealing, actually that was suspicious to me from the beginning.
> 
> I will add some code to dump the state of all cpupools to the BUG_ON to 
> see in which situation we are when the bug triggers.
OK, here is a first try of this, the patch iterates over all CPU pools 
and outputs some data if the BUG_ON
((sdom->weight * sdom->active_vcpu_count) > weight_left) condition triggers:
(XEN) CPU pool #0: 1 domains (SMP Credit Scheduler), mask: fffffffc003f
(XEN) CPU pool #1: 0 domains (SMP Credit Scheduler), mask: fc0
(XEN) CPU pool #2: 0 domains (SMP Credit Scheduler), mask: 1000
(XEN) Xen BUG at sched_credit.c:1010
....
The masks look proper (6 cores per node), the bug triggers when the 
first CPU is about to be(?) inserted.

HTH,
Andre.

-- 
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany