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From:   Vitaly Kuznetsov <vkuznets@redhat.com>
To:     Juergen Gross <jgross@suse.com>
Cc:     Jonathan Corbet <corbet@lwn.net>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org,
        x86@kernel.org, linux-doc@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH 6/6] x86/kvm: add boot parameter for setting max number
 of vcpus per guest
In-Reply-To: <62679c6a-2f23-c1d1-f54c-1872ec748965@suse.com>
References: <20210701154105.23215-1-jgross@suse.com>
 <20210701154105.23215-7-jgross@suse.com>
 <87h7gx2lkt.fsf@vitty.brq.redhat.com>
 <1ddffb87-a6a2-eba3-3f34-cf606a2ecba2@suse.com>
 <878s292k75.fsf@vitty.brq.redhat.com>
 <62679c6a-2f23-c1d1-f54c-1872ec748965@suse.com>
Date:   Wed, 14 Jul 2021 15:21:00 +0200
Message-ID: <8735sh2fr7.fsf@vitty.brq.redhat.com>
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Juergen Gross <jgross@suse.com> writes:

> On 14.07.21 13:45, Vitaly Kuznetsov wrote:
>
>> Personally, I'd vote for introducing a 'ratio' parameter then so
>> generally users will only have to set 'kvm.max_vcpus'.
>
> Okay.
>
> Default '4' then? Or '2 ^ (topology_levels - 2)' (assuming a
> topology_level of 3 on Intel: thread/core/socket and 4 on EPYC:
> thread/core/package/socket).

I'd suggest we default to '4' for both Intel and AMD as we haven't given
up completely on cross-vendor VMs (running AMD VMs on Intel CPUs and
vice versa). It would be great to leave a comment where the number comes
from of course.

-- 
Vitaly