Messages in this thread | | | Date | Wed, 17 Nov 2021 13:12:00 +0100 | Subject | Re: [PATCH v2 6/6] KVM: x86: Drop arbitraty KVM_SOFT_MAX_VCPUS | From | Paolo Bonzini <> |
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On 11/16/21 17:34, Vitaly Kuznetsov wrote: > KVM_CAP_NR_VCPUS is used to get the "recommended" maximum number of > VCPUs and arm64/mips/riscv report num_online_cpus(). Powerpc reports > either num_online_cpus() or num_present_cpus(), s390 has multiple > constants depending on hardware features. On x86, KVM reports an > arbitrary value of '710' which is supposed to be the maximum tested > value but it's possible to test all KVM_MAX_VCPUS even when there are > less physical CPUs available. > > Drop the arbitrary '710' value and return num_online_cpus() on x86 as > well. The recommendation will match other architectures and will mean > 'no CPU overcommit'. > > For reference, QEMU only queries KVM_CAP_NR_VCPUS to print a warning > when the requested vCPU number exceeds it. The static limit of '710' > is quite weird as smaller systems with just a few physical CPUs should > certainly "recommend" less. > > Suggested-by: Eduardo Habkost<ehabkost@redhat.com> > Signed-off-by: Vitaly Kuznetsov<vkuznets@redhat.com>
Given that KVM_SOFT_MAX_VCPUS has already been dropped in 5.16, I changed the commit message to
KVM: x86: Cap KVM_CAP_NR_VCPUS by KVM_CAP_MAX_VCPUS
It doesn't make sense to return the recommended maximum number of vCPUs which exceeds the maximum possible number of vCPUs.
Paolo
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