On Fri, 14 Dec 2012 15:36:22 -0200 Eduardo Habkost <ehabk...@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
