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From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <4c8330a1-8ba8-ff9e-bea2-8670df744e90@redhat.com>
Date: Mon, 24 Jul 2017 23:11:34 +0200
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Subject: Re: [Qemu-devel] [PATCH 1/4] target/i386: Use simple static
 property for "model-id"
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To: Igor Mammedov <imammedo@redhat.com>, Eduardo Habkost <ehabkost@redhat.com>
Cc: Jiri Denemark <jdenemar@redhat.com>, qemu-devel@nongnu.org, Richard Henderson <rth@twiddle.net>

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.
>=20
> 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 =3D (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 =3D ldl_le_p(&model[0]);
            *ebx =3D ldl_le_p(&model[4]);
            *ecx =3D ldl_le_p(&model[8]);
            *edx =3D ldl_le_p(&model[12]);

Paolo