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Re: [Xen-devel] [PATCH 2/2] xen: merge temporary vcpu pinning scenarios

Date: Tue, 23 Jul 2019 15:04:06 +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>

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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 16:29, Juergen Gross wrote: > On 23.07.19 16:14, Jan Beulich wrote: >> 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. > > So just to be sure: you are fine for me removing the pinning for NMIs? No, not the pinning as a whole. The forced CPU0 affinity should still remain. It's just that there's no correlation anymore between the CPU a vCPU was running on and the CPU it is to be pinned to (temporarily). What can go away if the #MC part of the logic. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel

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