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Re: [Xen-devel] [PATCH 2/2] xen: merge temporary vcpu pinning scenarios
- To: Juergen Gross <JGross@xxxxxxxx>
- From: Jan Beulich <JBeulich@xxxxxxxx>
- Date: Tue, 23 Jul 2019 14:14:42 +0000
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- Cc: Tim Deegan <tim@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, IanJackson <ian.jackson@xxxxxxxxxxxxx>, Dario Faggioli <dfaggioli@xxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Tue, 23 Jul 2019 14:15:42 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-topic: [Xen-devel] [PATCH 2/2] xen: merge temporary vcpu pinning scenarios
On 23.07.2019 16:03, Jan Beulich wrote:
> On 23.07.2019 15:44, Juergen Gross wrote:
>> On 23.07.19 14:42, Jan Beulich wrote:
>>> v->processor gets latched into st->processor before raising the softirq,
>>> but can't the vCPU be moved elsewhere by the time the softirq handler
>>> actually gains control? If that's not possible (and if it's not obvious
>>> why, and as you can see it's not obvious to me), then I think a code
>>> comment wants to be added there.
>>
>> You are right, it might be possible for the vcpu to move around.
>>
>> OTOH is it really important to run the target vcpu exactly on the cpu
>> it is executing (or has last executed) at the time the NMI/MCE is being
>> queued? This is in no way related to the cpu the MCE or NMI has been
>> happening on. It is just a random cpu, and so it would be if we'd do the
>> cpu selection when the softirq handler is running.
>>
>> One question to understand the idea nehind all that: _why_ is the vcpu
>> pinned until it does an iret? I could understand if it would be pinned
>> to the cpu where the NMI/MCE was happening, but this is not the case.
>
> Then it was never finished or got broken, I would guess.
Oh, no. The #MC side use has gone away in 3a91769d6e, without cleaning
up other code. So there doesn't seem to be any such requirement anymore.
Jan
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