[edk2-devel] 1024 VCPU limitation

[Pedro Falcato]

On Mon, Nov 7, 2022 at 5:28 PM Michael D Kinney <michael.d.kinney at intel.com>
wrote:

> Hi Pawel,
>
>
>
> I see the following union involved in the size of this structure.
>
>
>
> typedef union {
>
>   IA32_HANDOFF_STATUS       IA32HealthFlags;
>
>   X64_HANDOFF_STATUS        x64HealthFlags;
>
>   ITANIUM_HANDOFF_STATUS    ItaniumHealthFlags;
>
> } EFI_SEC_PLATFORM_INFORMATION_RECORD;
>
>
>
> IA32 is 4 bytes per CPU
>
> X64 is 4 bytes per CPU
>
> Itanium is 56 bytes per CPU
>
>
>
> We have removed the Itanium content from edk2 repo and it look like we
> missed this
>
> union.
>
Hi Mike,

I just want to note that I don't think you can remove
ITANIUM_HANDOFF_STATUS (in an upstreamable way at least) since it's
specified in the EFI PI spec, and it would also break any sort of ABI.
Maybe once you update the spec? Or maybe we could find a way to pass these
handoff statuses in multiple HOBs, or have v2 HOBs with UINT32 lengths
(with an appropriate spec update).

If you comment out the following line from the union does it resolve the
> issue?
>
>
>
>
> https://github.com/tianocore/edk2/blob/7c0ad2c33810ead45b7919f8f8d0e282dae52e71/MdePkg/Include/Ppi/SecPlatformInformation.h#L137
>
>
>
> I know this only increases the total number of CPUs that can be handled by
> a single 64kb HOB, so we would run into
>
> it again at a higher number of CPUs.  However, I think this gets the
> overhead per CPU down to 8 bytes, which should
>
> scale to about 8091 CPUs.
>
>
>
> Thanks,
>
>
>
> Mike
>
>
>
>
>
> *From:* Pawel Polawski <ppolawsk at redhat.com>
> *Sent:* Monday, November 7, 2022 3:52 AM
> *To:* devel at edk2.groups.io
> *Cc:* Dong, Eric <eric.dong at intel.com>; Laszlo Ersek <lersek at redhat.com>;
> Ni, Ray <ray.ni at intel.com>; Kumar, Rahul R <rahul.r.kumar at intel.com>;
> Kinney, Michael D <michael.d.kinney at intel.com>
> *Subject:* [edk2-devel] 1024 VCPU limitation
>
>
>
> Hi All,
>
>
>
> I am trying to run edk2 with more than 1024 VCPU. It looks like it is not
> possible
>
> at the moment and results in an ASSERT trigger.
>
>
>
> In the past the topic has been analyzed by Laszlo Ersek [1]. It turns out
> that the limit
>
> is result of HOB default allocation being limited to ~64KB, quoting
> original email thread:
>
>
>
> """
>
> If "NumberOfProcessors" is large enough, such as ~1024, then
> "BistInformationSize" will exceed ~64KB, and PeiServicesAllocatePool()
> will fail with EFI_OUT_OF_RESOURCES. The reason is that pool allocations
> in PEI are implemented with memory alloaction HOBs, and HOBs can't be
> larger than ~64KB. (See PeiAllocatePool() in
> "MdeModulePkg/Core/Pei/Memory/MemoryServices.c".)
>
> """
>
>
>
> Even with HOB allocation being changed, I am afraid it may break some
>
> compatibility on the DXE level. This is the reason I am looking for a more
> universal solution.
>
> I believe the same limitation exists for the physical x86 platforms with
> more than 1024 CPU.
>
>
>
> If someone has encountered the same issue or has knowledge that workaround
> / solution for
>
> this already exists or is being developed?
>
>
>
> [1]
> https://listman.redhat.com/archives/edk2-devel-archive/2021-June/msg01493
>
>
>
> Best regards,
>
> Pawel
>
>
> --
>
> *Paweł Poławski*
>
> Red Hat <https://www.redhat.com/> Virtualization
>
> ppolawsk at redhat.com
>
> @RedHat <https://twitter.com/redhat>   Red Hat
> <https://www.linkedin.com/company/red-hat>  Red Hat
> <https://www.facebook.com/RedHatInc>
>
> <https://red.ht/sig>
> 
>
>

-- 
Pedro Falcato


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