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

From: Shlomo Pongratz
Subject: Re: [Qemu-devel] [PATCH RFC V2 1/4] Use Aff1 with mpidr
Date: Thu, 21 May 2015 19:20:21 +0300

On Thursday, May 21, 2015, Pavel Fedin <address@hidden> wrote:

> 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,


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