Re: [edk2-devel] [PATCH v2 2/2] UefiCpuPkg/PiSmmCpuDxeSmm: Check BspIndex first before lock cmpxchg

["Ni, Ray" <ray.ni@intel.com>]

Jiaxin,
Can you separate the changes in 2 patches?
1 is to change (UINT32)-1 to MAX_UINT32, the other is to add the test before test-and-set.

Thanks,
Ray
> -----Original Message-----
> From: Wu, Jiaxin <jiaxin.wu@intel.com>
> Sent: Sunday, February 4, 2024 4:48 PM
> To: devel@edk2.groups.io
> Cc: Ni, Ray <ray.ni@intel.com>; Laszlo Ersek <lersek@redhat.com>; Dong,
> Eric <eric.dong@intel.com>; Zeng, Star <star.zeng@intel.com>; Gerd
> Hoffmann <kraxel@redhat.com>; Kumar, Rahul R <rahul.r.kumar@intel.com>;
> Kinney, Michael D <michael.d.kinney@intel.com>
> Subject: [PATCH v2 2/2] UefiCpuPkg/PiSmmCpuDxeSmm: Check BspIndex
> first before lock cmpxchg
> 
> This patch is to check BspIndex first before lock cmpxchg operation.
> If BspIndex has not been set, then do the lock cmpxchg, otherwise,
> the APs don't need to lock cmpxchg the BspIndex value since the BSP
> election has been done. It's the optimization to lower the resource
> contention caused by the atomic compare exchange operation, so as to
> improve the SMI performance for BSP election.
> 
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Zeng Star <star.zeng@intel.com>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Cc: Rahul Kumar <rahul1.kumar@intel.com>
> Cc: Kinney Michael D <michael.d.kinney@intel.com>
> Signed-off-by: Jiaxin Wu <jiaxin.wu@intel.com>
> ---
>  UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
> b/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
> index e988ce0542..085aa91286 100644
> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
> @@ -1652,15 +1652,17 @@ SmiRendezvous (
>              }
>            } else {
>              //
>              // Platform hook fails to determine, use default BSP election
> method
>              //
> -            InterlockedCompareExchange32 (
> -              (UINT32 *)&mSmmMpSyncData->BspIndex,
> -              (UINT32)-1,
> -              (UINT32)CpuIndex
> -              );
> +            if (mSmmMpSyncData->BspIndex == MAX_UINT32) {
> +              InterlockedCompareExchange32 (
> +                (UINT32 *)&mSmmMpSyncData->BspIndex,
> +                MAX_UINT32,
> +                (UINT32)CpuIndex
> +                );
> +            }
>            }
>          }
>        }
> 
>        //
> --
> 2.16.2.windows.1



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