From: Paolo Bonzini <pbonzini@redhat.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>, kvm@vger.kernel.org
Cc: Sean Christopherson <seanjc@google.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>,
Eduardo Habkost <ehabkost@redhat.com>,
Marc Zyngier <maz@kernel.org>, Andrew Jones <drjones@redhat.com>,
Huacai Chen <chenhuacai@kernel.org>,
Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
Anup Patel <anup.patel@wdc.com>,
Paul Mackerras <paulus@ozlabs.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Janosch Frank <frankja@linux.ibm.com>,
kvm-ppc@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-mips@vger.kernel.org, kvm-riscv@lists.infradead.org,
linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 6/6] KVM: x86: Drop arbitraty KVM_SOFT_MAX_VCPUS
Date: Wed, 17 Nov 2021 12:12:00 +0000 [thread overview]
Message-ID: <7cd420c0-4fe5-7c37-5eb8-da82b277ff60@redhat.com> (raw)
In-Reply-To: <20211116163443.88707-7-vkuznets@redhat.com>
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
prev parent reply other threads:[~2021-11-17 12:12 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-16 16:34 [PATCH v2 0/6] KVM: Cap KVM_CAP_NR_VCPUS by KVM_CAP_MAX_VCPUS and re-purpose it on x86 Vitaly Kuznetsov
2021-11-16 16:34 ` [PATCH v2 1/6] KVM: arm64: Cap KVM_CAP_NR_VCPUS by kvm_arm_default_max_vcpus() Vitaly Kuznetsov
2021-11-17 9:13 ` Marc Zyngier
2021-11-17 12:07 ` Paolo Bonzini
2021-11-16 16:34 ` [PATCH v2 2/6] KVM: MIPS: Cap KVM_CAP_NR_VCPUS by KVM_CAP_MAX_VCPUS Vitaly Kuznetsov
2021-11-16 16:34 ` [PATCH v2 3/6] KVM: PPC: " Vitaly Kuznetsov
2021-11-16 16:34 ` [PATCH v2 4/6] KVM: RISC-V: " Vitaly Kuznetsov
2021-11-17 5:14 ` Anup Patel
2021-11-16 16:34 ` [PATCH v2 5/6] KVM: s390: Cap KVM_CAP_NR_VCPUS by num_online_cpus() Vitaly Kuznetsov
2021-11-17 7:33 ` Christian Borntraeger
2021-11-16 16:34 ` [PATCH v2 6/6] KVM: x86: Drop arbitraty KVM_SOFT_MAX_VCPUS Vitaly Kuznetsov
2021-11-17 12:12 ` Paolo Bonzini [this message]
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