Re: [edk2-devel] [PATCH 2/5] UefiCpuPkg/MpInitLib: Add support for multiple HOBs to GetBspNumber()

["Laszlo Ersek" <lersek@redhat.com>]

On 2/15/24 10:31, Gerd Hoffmann wrote:
> Remove the MpHandOff parameter.  This is not useful in case multiple
> HOBs are present in the system.  The function will use GetMpHandOffHob()
> to loop over all HOBs instead.
> 
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  UefiCpuPkg/Library/MpInitLib/MpLib.c | 26 ++++++++++++++++----------
>  1 file changed, 16 insertions(+), 10 deletions(-)
> 
> diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> index e0a2366073a7..8e6cf50ed171 100644
> --- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
> +++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> @@ -1894,26 +1894,32 @@ CheckAllAPs (
>  /**
>    This function Get BspNumber.
>  
> -  @param[in] MpHandOff        Pointer to MpHandOff
>    @return                     BspNumber
>  **/
>  UINT32
>  GetBspNumber (
> -  IN CONST MP_HAND_OFF  *MpHandOff
> +  VOID
>    )
>  {
> -  UINT32  ApicId;
> -  UINT32  BspNumber;
> -  UINT32  Index;
> +  UINT32       ApicId;
> +  UINT32       BspNumber;
> +  UINT32       Index;
> +  MP_HAND_OFF  *MpHandOff;
>  
>    //
>    // Get the processor number for the BSP
>    //
>    BspNumber = MAX_UINT32;
>    ApicId    = GetInitialApicId ();
> -  for (Index = 0; Index < MpHandOff->CpuCount; Index++) {
> -    if (MpHandOff->Info[Index].ApicId == ApicId) {
> -      BspNumber = Index;
> +
> +  for (MpHandOff = GetMpHandOffHob (0);
> +       MpHandOff != NULL;
> +       MpHandOff = GetMpHandOffHob (MpHandOff->ProcessorIndex + MpHandOff->CpuCount))
> +  {
> +    for (Index = 0; Index < MpHandOff->CpuCount; Index++) {
> +      if (MpHandOff->Info[Index].ApicId == ApicId) {
> +        BspNumber = MpHandOff->ProcessorIndex + Index;
> +      }
>      }
>    }
>  

(I'm missing the larger picture here -- is this related to the problem
-- too many CPUs to fit their infos into a single HOB -- that Pawel
worked on for a while?

"UefiCpuPkg/Library/MpInitLib/MpHandOff.h" was created in commit
8bb018afaf2a ("UefiCpuPkg: Create MpHandOff.", 2023-07-11); I don't have
memories from that time frame. Either way, I do have a question /
observation here:)

The outer loop is suboptimal, IMO, to just open-coding another HOB scan
-- this approach looks quadratic, even though it could be linear. More
or less, as proposed, we call GetMpHandOffHob() for each MP_HAND_OFF
HOB, which will scan n/2 HOBs on average. (Even if the GUID HOB list is
sorted by ProcessorIndex, we'll scan 1 + 2 + 3 +... HOBs.) But if we
open-coded GetFirstGuidHob() and GetNextGuidHob() here, then a single
scan would suffice.

Laszlo

> @@ -1941,7 +1947,7 @@ SwitchApContext (
>    UINTN   Index;
>    UINT32  BspNumber;
>  
> -  BspNumber = GetBspNumber (MpHandOff);
> +  BspNumber = GetBspNumber ();
>  
>    for (Index = 0; Index < MpHandOff->CpuCount; Index++) {
>      if (Index != BspNumber) {
> @@ -2191,7 +2197,7 @@ MpInitLibInitialize (
>      }
>  
>      CpuMpData->CpuCount  = MpHandOff->CpuCount;
> -    CpuMpData->BspNumber = GetBspNumber (MpHandOff);
> +    CpuMpData->BspNumber = GetBspNumber ();
>      CpuInfoInHob         = (CPU_INFO_IN_HOB *)(UINTN)CpuMpData->CpuInfoInHob;
>      for (Index = 0; Index < CpuMpData->CpuCount; Index++) {
>        InitializeSpinLock (&CpuMpData->CpuData[Index].ApLock);



-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#115590): https://edk2.groups.io/g/devel/message/115590
Mute This Topic: https://groups.io/mt/104369845/7686176
Group Owner: devel+owner@edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/unsub [rebecca@openfw.io]
-=-=-=-=-=-=-=-=-=-=-=-