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

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

On 2/5/24 06:06, Ni, Ray wrote:
> 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; I'll defer to Ray on this series.

Laszlo

> 
> 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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