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Re: [Qemu-devel] [PATCH 3/3] target-i386: replace cpuid_*features fields
From: |
Igor Mammedov |
Subject: |
Re: [Qemu-devel] [PATCH 3/3] target-i386: replace cpuid_*features fields with a feature word array |
Date: |
Fri, 14 Dec 2012 18:47:20 +0100 |
On Fri, 14 Dec 2012 15:36:22 -0200
Eduardo Habkost <address@hidden> wrote:
> On Fri, Dec 14, 2012 at 06:20:41PM +0100, Andreas Färber wrote:
> > Am 14.12.2012 17:52, schrieb Eduardo Habkost:
> > > On Fri, Dec 14, 2012 at 04:14:32PM +0100, Andreas Färber wrote:
> > >> Am 12.12.2012 23:22, schrieb Eduardo Habkost:
[...]
> >
> > >> The clock code using first_cpu looks solvable; what about CR4 and MSR
> > >> helpers, how performance-sensitive are they? (if they're not yet using
> > >> X86CPU for something else)
> > >
> > > I guess any CPU-state code inside QEMU is not performance-sensitive, as
> > > it woud already require switching between KVM kernelspace and QEMU
> > > userspace.
> >
> > I mean target-i386/[misc_]helper.c and thus TCG, IIUC. :)
>
> Oh, right. I wonder how much performance impact it would have, if people
> are already using TCG.
>
> 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.
>
> --
> Eduardo
--
Regards,
Igor
- Re: [Qemu-devel] [PATCH 3/3] target-i386: replace cpuid_*features fields with a feature word array, (continued)
Re: [Qemu-devel] [PATCH 3/3] target-i386: replace cpuid_*features fields with a feature word array, Andreas Färber, 2012/12/14