Re: [Qemu-devel] [PATCH RFC V2 1/4] Use Aff1 with mpidr

[Shlomo Pongratz <shlomopongratz@gmail.com>]

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On Thursday, May 21, 2015, Pavel Fedin <p.fedin@samsung.com> wrote:

>  Hello!
>
> > In order to support up to 128 cores with GIC-500 (GICv3 implementation)
> > affinity1 must be used. GIC-500 support up to 32 clusters with up to
> > 8 cores in a cluster. So for example, if one wishes to have 16 cores,
> > the options are: 2 clusters of 8 cores each, 4 clusters with 4 cores each
>
>  I have found one more concern. Are you really sure about this scheme ? I
> am currently
> experimenting with KVM, and it seems to have 16 CPUs per cluster, at least
> on my machine.
> Actually i suggest that KVM inherits the mapping from the host. Can we do
> the same?
>  I will take a look at kvmtool, how it determines these IDs. But hardcoded
> scheme is
> definitely wrong.
>
>  Cc'ed Ashok because he might also be interested.
>
> Kind regards,
> Pavel Fedin
> Expert Engineer
> Samsung Electronics Research center Russia
>
> Hi Pavel,

I can only quote from GIC-500 document (
http://infocenter.arm.com/help/topic/com.arm.doc.ddi0516b/DDI0516B_gic5000_r0p0_trm.pdf)
which is currently the only GICv3 implementation) I'll recheck the GICv3
when I'll return to work on Monday.

>From section 1.3 features.

The GIC-500 provides registers for managing interrupt sources, interrupt
behavior, and interrupt
routing to one or more cores. It supports:
• Multiprocessor environments with up to 128 cores.
• Up to 32 affinity-level 1 clusters.
• Up to eight cores for each cluster.

I guess your hardware uses different GIC.

Best regards,

S.P.

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