Re: [Qemu-devel] [PATCH 3/3] target-i386: replace cpuid_*features fields with a feature word array

[Igor Mammedov <imammedo@redhat.com>]

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 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