Hi MdePkg and UefiCpuPkg maintainers and reviewers

Recently, we met a performance issue when waking up disabled APs.
There is usage where BIOS needs to disable all APs, do something and then enable all APs.
Now, we are using the MpService PPI/Protocol EnableDisableAP(). This function can only enable/disable one AP each time.
To enable one AP, MP service needs to send INIT-SIPI-SIPI, which takes around 10ms.
And now, we will have more than 10 APs in a client platform, and it will take more than 100ms.
The function definition of EnableDisableAP is:
typedef
EFI_STATUS
(EFIAPI *EFI_MP_SERVICES_ENABLEDISABLEAP)(
  IN  EFI_MP_SERVICES_PROTOCOL  *This,
  IN  UINTN                     ProcessorNumber,
  IN  BOOLEAN                   EnableAP,
  IN  UINT32                    *HealthFlag OPTIONAL
  );
The input parameter ProcessorNumber accepts a range from 0 to the total number of logical processors minus 1.

To support enable/disable AP parallel, I have below solutions:

Solution1:
Let input parameter ProcessorNumber accept a MAX_UINTN also. MAX_UINTN means to enable/disable all APs.
The draft PR is at https://github.com/tianocore/edk2/pull/6453 When the parameter is MAX_UINTN, EnableDisableAP() will enable/disable APs in a parallel way.
                However, we need to change below header files
                                MdePkg\Include\Protocol\MpService.h
                                MdePkg\Include\Ppi\MpServices.h
                                UefiCpuPkg\Include\Ppi\MpServices2.h
                The above two follow PI spec. We need to modify the PI spec first.

Solution2:
                Similar with solution1, but to avoid violating spec, add a new Protocol named MpServices2. Only change below header files.
                                UefiCpuPkg\Include\Ppi\MpServices2.h
UefiCpuPkg\Include\Protocol\MpServices2.h (new)
                The MdePkg part remains no change.

Solution3:
                MpService create new PPI/Protocol to only contain one function EnableDisableAllAps(), which will enable/disable all APs in a parallel way.

Solution4:
                Add PPI/Protocol notify in MpLib. The notify call back function will set WakeUpByInitSipiSipi to True. Similar code is removed in https://github.com/tianocore/edk2/pull/6303/commits/f1f8374381019169d421a65a896ab42ed5338c1e
                When users need to disable and then enable cores, the flow will be:

  1.  Send Init to all APs. (to disable all APs)
  2.  Do things that user need to do when all APs are disabled
  3.  Notify callback function
  4.  Use StartupAllAPs() from existing PPI/Protocol to wake up all APs.
The flow is similar with how S3 SMM code take control APs and then give the control back in old days.

Personally, I prefer solution1. It is simpler, but it does violate spec.
Please let me know your comments or any new idea, please share.

Thanks
Zhiguang



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