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Date: Fri, 14 Dec 2012 18:47:20 +0100
From: Igor Mammedov <imammedo@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 3/3] target-i386: replace cpuid_*features
 fields with a feature word array
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To: Eduardo Habkost <ehabkost@redhat.com>
Cc: Andreas =?UTF-8?B?RsOkcmJlcg==?= <afaerber@suse.de>, qemu-devel@nongnu.org

On Fri, 14 Dec 2012 15:36:22 -0200
Eduardo Habkost <ehabkost@redhat.com> wrote:

> On Fri, Dec 14, 2012 at 06:20:41PM +0100, Andreas F=C3=A4rber wrote:
> > Am 14.12.2012 17:52, schrieb Eduardo Habkost:
> > > On Fri, Dec 14, 2012 at 04:14:32PM +0100, Andreas F=C3=A4rber wrote:
> > >> Am 12.12.2012 23:22, schrieb Eduardo Habkost:
[...]
> >=20
> > >> The clock code using first_cpu looks solvable; what about CR4 and MSR
> > >> helpers, how performance-sensitive are they? (if they're not yet usi=
ng
> > >> X86CPU for something else)
> > >=20
> > > I guess any CPU-state code inside QEMU is not performance-sensitive, =
as
> > > it woud already require switching between KVM kernelspace and QEMU
> > > userspace.
> >=20
> > I mean target-i386/[misc_]helper.c and thus TCG, IIUC. :)
>=20
> Oh, right. I wonder how much performance impact it would have, if people
> are already using TCG.
>=20
> Anyway, would this really have any impact at all? I mean:
> ENV_GET_CPU(env) is basically subtracing an constant offset from 'env'.
> So I expect similar code to be generated, just using a different offset
> from 'env' to get the cpuid_features field.
ENV_GET_CPU(env) does dynamic_cast which is expensive.


>=20
> --=20
> Eduardo


--=20
Regards,
  Igor