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Date: Tue, 27 Aug 2013 15:18:16 +0200
From: =?iso-8859-1?Q?Beno=EEt?= Canet <benoit.canet@irqsave.net>
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Subject: Re: [Qemu-devel] KVM guest cpu L3 cache and cpufreq
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To: Eduardo Habkost <ehabkost@redhat.com>
Cc: =?iso-8859-1?Q?Beno=EEt?= Canet <benoit.canet@irqsave.net>, Gleb Natapov <gleb@redhat.com>, qemu-devel@nongnu.org, Igor Mammedov <imammedo@redhat.com>, pbonzini@redhat.com, Andreas =?iso-8859-1?Q?F=E4rber?= <afaerber@suse.de>


Hello Eduardo,

I read a bit about caches on wikipedia.

If I understand correctly changing the CPUID L3 cache infos in QEMU will =
change
the value displayed in the guest /proc/cpuinfo but will not change the si=
ze of
the l3 cache used by the hardware. So I am chasing a cosmetic bug.
If it right ?

> > Do you have some recommandations regarding the other fields of the ed=
x register ?
>=20
> Probably it will be a good idea to let each CPU model have their own
> defaults for the cache information.

Do you mean querying the host CPUID registers and forwarding the values t=
o the
guest ?

>=20
> > What would be an acceptable user interface to set this ?
>=20
> Things I can remember from the top of my head:
>=20
>  * It would be interesting to redo this patch, before doing anything el=
se:
>    https://github.com/ehabkost/qemu-hacks/commit/10b675fa1269a65a553586=
545fdbcd95ace79d65
>  * We need to keep compatibility on existing machine-types (not change
>    the cache size);
>  * If some information is reported on multiple CPUID leaves, we need to
>    keep them consistent with each other (see the FIXME comments on the
>    URL above);
I could write a patch to fix broken CPUID leaves.

But how would it work regarding compatibility ? Is it right to just fix t=
he
leaves or does the machine type rule apply here ?

Best regards

Beno=EEt