linux-kernel - RE: [PATCH] KVM: selftests: x86: Avoid using SSE/AVX instructions

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Message-ID: <87ikull0ln.fsf@redhat.com>
Date: Tue, 24 Sep 2024 14:04:04 +0200
From: Vitaly Kuznetsov <vkuznets@...hat.com>
To: David Laight <David.Laight@...LAB.COM>
Cc: Jan Richter <jarichte@...hat.com>, "linux-kernel@...r.kernel.org"
 <linux-kernel@...r.kernel.org>, "kvm@...r.kernel.org"
 <kvm@...r.kernel.org>, Paolo Bonzini <pbonzini@...hat.com>, Sean
 Christopherson <seanjc@...gle.com>
Subject: RE: [PATCH] KVM: selftests: x86: Avoid using SSE/AVX instructions

David Laight <David.Laight@...LAB.COM> writes:

> From: Vitaly Kuznetsov <vkuznets@...hat.com>
>> Sent: 20 September 2024 16:44
>> 
>> Some distros switched gcc to '-march=x86-64-v3' by default and while it's
>> hard to find a CPU which doesn't support it today,
>
> I didn't think that any of the Atom based cpu supported AVX.
> I'm pretty sure one we use that are still in production as
> server motherboards don't support it.
>
> Doesn't -v3 also require support for the VEX encoding.
> Which removes a lot of perfectly reasonable cpu?
>

Well, distros making such decision are obviously not very interested in
running on these CPUs then :-) In this particular case, the distro was
Centos Stream 10 and they are very explicit about the decision:
https://developers.redhat.com/articles/2024/01/02/exploring-x86-64-v3-red-hat-enterprise-linux-10#new_cpu_capabilities_in_x86_64_v3

and 'gcc -v' tells me

Configured with: ../configure ... --with-arch_64=x86-64-v3  ...
...
gcc version 14.2.1 20240801 (Red Hat 14.2.1-1) (GCC) 

-- 
Vitaly