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Peter Anvin" Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Mon, Jan 20, 2025, Bagas Sanjaya wrote: > On Sun, Jan 19, 2025 at 12:04:04PM +0100, Toralf F=C3=B6rster wrote: > > I was wondering why I cannot put a lower value here during make oldconf= ig: The lower limit of 1024 in the Kconfig exists to ensure backwards compatibi= lity. CONFIG_KVM_MAX_NR_VCPUS is effectively exposed to userspace via KVM_CAP_MAX= _VCPUS, and prior to the Kconfig KVM hardcoded KVM_CAP_MAX_VCPUS to 1024. I did float the idea of setting the range to 1 - 4096, but we opted to go w= ith the conservative approach because the benefits are relatively minor, and we= didn't want to risk indirectly breaking userspace. > > Maximum number of vCPUs per KVM guest (KVM_MAX_NR_VCPUS) [1024] (NEW)= 16 > > Maximum number of vCPUs per KVM guest (KVM_MAX_NR_VCPUS) [1024] (NEW)= 8 > > Maximum number of vCPUs per KVM guest (KVM_MAX_NR_VCPUS) [1024] (NEW) > >=20 >=20 > Hi Toralf, >=20 > From arch/x86/kvm/Kconfig: >=20 > >config KVM_MAX_NR_VCPUS > > int "Maximum number of vCPUs per KVM guest" > > depends on KVM > > range 1024 4096 > > default 4096 if MAXSMP > > default 1024 > > help > > Set the maximum number of vCPUs per KVM guest. Larger values will inc= rease > > the memory footprint of each KVM guest, regardless of how many vCPUs = are > > created for a given VM. >=20 > I don't know your use case, but you can safely choose the default (1024). >=20 > Thanks. >=20 > --=20 > An old man doll... just what I always wanted! - Clara