Re: [Qemu-devel] [PATCH 1/4] target/i386: Use simple static property for "model-id"

[Eduardo Habkost]

On Mon, Jul 24, 2017 at 11:11:34PM +0200, Paolo Bonzini wrote:
> On 18/07/2017 13:29, Igor Mammedov wrote:
> >> It may add a few additional CPU cycles, but I really doubt we can
> >> find a workload where CPUID speed has measurable impact.  See,
> >> for example, how expensive the kernel KVM CPUID code
> >> (kvm_cpuid(), kvm_find_cpuid_entry()) is.
> > 
> > I don't expect that it would affect KVM, but for TCG any instruction
> > execution is 'fast' path, so I'd leave current cpu_x86_cpuid()
> > not to loose those few cycles, it's not worth sacrifice for the sake of 
> > cleanup.
> 
> It's not like this does a QOM property lookup or anything.  I think the
> patch is a good idea.
> 
> Even simpler way to write the cpuid code:
> 
>             int base = (index - 0x80000002) * 16;
>             char model[16];
> 
>             if (strnlen(env->model_id, base) < base) {
>                 memset(model, 0, sizeof(model));
>             } else {
>                 strncpy(model, env->model_id + base, sizeof(model));
>             }
>             *eax = ldl_le_p(&model[0]);
>             *ebx = ldl_le_p(&model[4]);
>             *ecx = ldl_le_p(&model[8]);
>             *edx = ldl_le_p(&model[12]);

Neat.  I will use it in v2.  Thanks!

-- 
Eduardo