> On 20-Feb-2024, at 21:46, Gerd Hoffmann <kra...@redhat.com> wrote:
>
> On Tue, Feb 20, 2024 at 03:50:57PM +0000, Daniel P. Berrangé wrote:
>> On Tue, Feb 20, 2024 at 09:12:04PM +0530, Ani Sinha wrote:
>>> Since commit f10a570b093e6 ("KVM: x86: Add CONFIG_KVM_MAX_NR_VCPUS to allow
>>> up to 4096 vCPUs")
>>> Linux kernel can support upto a maximum number of 4096 vCPUS when MAXSMP is
>>> enabled in the kernel. At present, QEMU has been tested to correctly boot a
>>> linux guest with 4096 vcpus both with edk2 and seabios firmwares.
>>> So bump up the value max_cpus to 4096 for q35 machines versions 9 and newer.
>>> Q35 machines versions 8.2 and older continue to support 1024 maximum vcpus
>>> as before for compatibility reasons.
>>>
>>> If KVM is not able to support the specified number of vcpus, QEMU would
>>> return the following error messages:
>>>
>>> $ ./qemu-system-x86_64 -cpu host -accel kvm -machine q35 -smp 1728
>>> qemu-system-x86_64: -accel kvm: warning: Number of SMP cpus requested
>>> (1728) exceeds the recommended cpus supported by KVM (12)
>>> qemu-system-x86_64: -accel kvm: warning: Number of hotpluggable cpus
>>> requested (1728) exceeds the recommended cpus supported by KVM (12)
>>> Number of SMP cpus requested (1728) exceeds the maximum cpus supported by
>>> KVM (1024)
>>>
>>> Cc: Daniel P. Berrangé <berra...@redhat.com>
>>> Cc: Igor Mammedov <imamm...@redhat.com>
>>> Cc: Michael S. Tsirkin <m...@redhat.com>
>>> Cc: Julia Suvorova <jus...@redhat.com>
>>> Cc: kra...@redhat.com
>>> Signed-off-by: Ani Sinha <anisi...@redhat.com>
>>> ---
>>> hw/i386/pc_q35.c | 3 ++-
>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> Changelog:
>>> v3: bump up to 4096 vcpus. It has now been tested to work with edk2.
>>> See RH Jira: https://issues.redhat.com/browse/RHEL-22202
>>
>> That bug indicates a dependancy on a EDK2 patch
>>
>>
>> https://github.com/kraxel/edk2/commit/7a03c17f0f4f4a9003d77db2660c8e087604b2f0
>>
>> we'll need to rebase the EDK2 ROMs in QEMU to get that included.
>
> Which will btw take a while. edk2 is in freeze for the 2024-02 release
> right now, I expect the changes land upstream shortly thereafter and
> will be part of the 2024-05 release. So end may / early june would be
> the time when rebasing to release, or somewhen in march or april when we
> rebase to a git snapshot ...
>
>> Meanwhile, plesae at least call out this EDK2 commit as a
>> pre-requisite in the commit message, so people know the
>> EDK2 ROMs in QEMU won't work (yet).
>
> That surely makes sense.
>
> Oh, and it's more than just that one commit. I don't think it makes
> sense to compile a list of commits given this is a moving target
> (upstream review is in progress right now).
Looking at the edk2 GH, are these the PR that are waiting for upstream
review/merge that relate to vcpu scaling?
https://github.com/tianocore/edk2/pull/5375
https://github.com/tianocore/edk2/pull/5327
