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

[Paolo Bonzini]

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]);

Paolo