[edk2-devel] [PATCH v1 2/2] UefiCpuPkg/PiSmmCpuDxeSmm: Check BspIndex first before lock cmpxchg

["Wu, Jiaxin" <jiaxin.wu@intel.com>]

This patch is to check BspIndex first before lock cmpxchg operation.
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>
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..479024d294 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 == (UINT32)-1) {
+              InterlockedCompareExchange32 (
+                (UINT32 *)&mSmmMpSyncData->BspIndex,
+                (UINT32)-1,
+                (UINT32)CpuIndex
+                );
+            }
           }
         }
       }
 
       //
-- 
2.16.2.windows.1



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