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Date: Thu, 31 Oct 2013 13:50:05 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] RFC: spapr: introduce smt_cpu_index
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To: Alexey Kardashevskiy <aik@ozlabs.ru>
Cc: Alexander Graf <agraf@suse.de>, qemu-devel@nongnu.org, qemu-ppc@nongnu.org, Badari Pulavarty <pbadari@linux.vnet.ibm.com>, Paul Mackerras <paulus@samba.org>, =?UTF-8?B?QW5kcmVhcyBGw6RyYmVy?= <afaerber@suse.de>, David Gibson <david@gibson.dropbear.id.au>

Il 31/10/2013 10:28, Alexey Kardashevskiy ha scritto:
> This is not really a patch to accept or review, this is a conversation
> starter.
>=20
> Cc: Badari Pulavarty  <pbadari@linux.vnet.ibm.com>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: David Gibson <david@gibson.dropbear.id.au>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Andreas F=C3=A4rber <afaerber@suse.de>
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
>=20
> ---
>=20
> Normall CPUState::cpu_index is used to pick the right CPU for various
> operations. However default consecutive numbering does not always work
> for PPC64.
>=20
> For example, on POWER7 (which supports 4 threads per core),
> "-smp 8,threads=3D4" should create CPUs with indexes 0,1,2,3,4,5,6,7 an=
d
> "-smp 8,threads=3D1" should create CPUs with indexes 0,4,8,12,16,20,24,=
28.
>=20
> These indexes are reflected in /proc/device-tree/cpus/PowerPC,POWER7@XX
> and used to call KVM VCPU's ioctl.

I think these two uses should be separated, even if they use the same
formula.  Define a PPC-specific concept, used by TCG as well, and make
kvm_arch_vcpu_id use it.

In other words:

- the hw/ppc/spapr* changes should not use kvm_arch_vcpu_id and
kvm_arch_get_vcpu_by_id, but something like ppc_get_vcpu_dt_id and
ppc_get_vcpu_by_dt_id.

- the comment for the new field should be something like /* The CPU
index used in the device tree.  KVM uses this index too.  */

- kvm_arch_vcpu_id can be a simple wrapper for ppc_get_vcpu_dt_id; no
need for the new kvm_arch_get_vcpu_by_id, and no kvm-stub.c changes
should be necessary either.

- everything else seems fine.

> 2. Apply the patch below and make sure it does not break x86/ARM/s390
> with and without KVM (does not it?);

If you do it right (i.e. do not touch kvm-stub.c) it should "obviously"
not break anything outside PPC.

Paolo