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RE: [Xen-devel] Re: [PATCH 1/4] CPU online/offline support in Xen

To: Christoph Egger <Christoph.Egger@xxxxxxx>, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>
Subject: RE: [Xen-devel] Re: [PATCH 1/4] CPU online/offline support in Xen
From: "Ke, Liping" <liping.ke@xxxxxxxxx>
Date: Wed, 17 Sep 2008 21:14:59 +0800
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Cc: "Tian, Kevin" <kevin.tian@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Shan, Haitao" <haitao.shan@xxxxxxxxx>, Gavin Maltby <Gavin.Maltby@xxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>, Haitao Shan <maillists.shan@xxxxxxxxx>
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Thread-topic: [Xen-devel] Re: [PATCH 1/4] CPU online/offline support in Xen
Hi, Egger
Thanks a lot about your answer. Just look through your patch and want to get 
some help:

1. When MCE happens, will all of the cores (even in different socket) all be 
brought into MCE handler in AMD platform (such as K8) too? So every core will 
enter and execute k8_machine_check handler? When mce happened, this handler 
will enter N (number of cores) times.

2. When doing send_guest_trap, if dom0->vcpu0->processor = 0 while in 
nmi_mce_softirq, cur_cpu = 1, when set affinity, we should bind dom0->vcpu0 
with cur_cpu 1 instead of its original bindings [cpu_set(cpu, affinity) vs 
cpu_set(st->processor, affinity)]? Otherwise the affinity has e no changes and 
need not restore? Not sure about this.

3. If several vcpus are running (belongs dom0 or other domains) when MCA 
happens, if we don't pause other vcpus except dom0.vcpu0 and let them into 
idle, maybe we can't make sure that those vcpus will still be scheduled in an 
unstable environment? At the same time, other pcpu might be in k8_machine_check 
handler concurrently?

Thanks a lot for your answer!

-----Original Message-----
From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx 
[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Christoph Egger
Sent: 2008年9月17日 17:44
To: Jiang, Yunhong
Cc: Tian, Kevin; xen-devel@xxxxxxxxxxxxxxxxxxx; Shan, Haitao; Gavin Maltby; 
Keir Fraser; Haitao Shan
Subject: Re: [Xen-devel] Re: [PATCH 1/4] CPU online/offline support in Xen

On Wednesday 17 September 2008 11:20:57 Jiang, Yunhong wrote:
> >-----Original Message-----
> >From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
> >[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Jan Beulich
> >Sent: 2008年9月17日 15:06
> >To: Christoph Egger; Gavin Maltby
> >Cc: Haitao Shan; Tian, Kevin; xen-devel@xxxxxxxxxxxxxxxxxxx;
> >Shan, Haitao; Keir Fraser
> >Subject: Re: [Xen-devel] Re: [PATCH 1/4] CPU online/offline
> >support in Xen
> >
> >>>> Gavin Maltby <Gavin.Maltby@xxxxxxx> 17.09.08 06:17 >>>
> >>
> >>I don't see this as a problem for machine check correctness.
> >>
> >>If dom0 asks to offline a cpu (because it believes the cpu is
> >
> >busted and
> >
> >>a threat to uptime), that decision is fundamentally asynchronous
> >>to the actual error handling that occured at machine check exception
> >>time:
> >>
> >>  - running in whatever context
> >>  - MCE occurs
> >>  - trap to hypervisor MCE handler
> >>       . this decides on hypervisor panic, or other appropriate
> >>         immediate (in handler) response
> >>       . telemetry forwarded to dom0 for logging and analysis
> >>  - assume no hypervisor panic
> >>  - eons pass during which any unconstrained bad data remaining
> >>    after initial handling may go anywhere
> >>  - dom0 gets telemetry and let's say diagnoses a fault and
> >>    decides to call back into the hypervisor to offline the
> >>    offending cpu
> >>
> >>Note the "eons pass" bit;  tonnes of instructions may run on the
> >>bad cpu in this time, and a few more for some offline delay won't
> >>hurt.
> >
> >Shouldn't this possibly be handled the other way around: If a
> >recoverable
> >MCE happened, immediately stop scheduling anything on the affected
> >CPU(s), until Dom0 tells you otherwise (and of course as long as there
> >remains at least one CPU to run on).
> Current MCE handling in Xen has no mechanism to achieve this.

It has since c/s 17968.


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