Re: [PATCH] UefiCpuPkg/PiSmmCpuDxeSmm: Improve the performance of GetFreeToken()

["Dong, Eric" <eric.dong@intel.com>]

Hi Ray,

I think this patch misses the initialization for gSmmCpuPrivate->FirstFreeToken variable, right?
Should add below code in InitializeDataForMmMp(), right?
  gSmmCpuPrivate->FirstFreeToken = AllocateTokenBuffer ();

Also the copy right year should 2020 instead of 2021.

Thanks,
Eric

-----Original Message-----
From: Ray Ni <niruiyu@users.noreply.github.com> 
Sent: Friday, April 10, 2020 3:41 AM
To: devel@edk2.groups.io
Cc: Ni, Ray <ray.ni@intel.com>; Dong, Eric <eric.dong@intel.com>; Zeng, Star <star.zeng@intel.com>
Subject: [PATCH] UefiCpuPkg/PiSmmCpuDxeSmm: Improve the performance of GetFreeToken()

Today's GetFreeToken() runs at the algorithm complexity of O(n) where n is the size of the token list.

The change introduces a new global variable FirstFreeToken and it always points to the first free token. So the algorithm complexity of GetFreeToken() decreases from O(n) to O(1).

The improvement matters when some SMI code uses StartupThisAP() service for each of the AP such that the algorithm complexity becomes O(n) * O(m) where m is the AP count.

As next steps,
1. PROCEDURE_TOKEN.Used field can be optimized out because all tokens before FirstFreeToken should have "Used" set while all after FirstFreeToken should have "Used" cleared.
2. ResetTokens() can be optimized to only reset tokens before FirstFreeToken.

Signed-off-by: Ray Ni <ray.ni@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
---
 UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c      | 71 ++++++++--------------
 UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h |  3 +-
 2 files changed, 27 insertions(+), 47 deletions(-)

diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c b/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
index c285a70ebb..7a223410d7 100644
--- a/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
+++ b/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
@@ -1,7 +1,7 @@
 /** @file
 SMM MP service implementation
 
-Copyright (c) 2009 - 2020, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2009 - 2021, Intel Corporation. All rights reserved.<BR>
 Copyright (c) 2017, AMD Incorporated. All rights reserved.<BR>
 
 SPDX-License-Identifier: BSD-2-Clause-Patent @@ -453,6 +453,11 @@ ResetTokens (
 
     Link = GetNextNode (&gSmmCpuPrivate->TokenList, Link);
   }
+
+  //
+  // Reset the FirstFreeToken to the beginning of token list upon exiting SMI.
+  //
+  gSmmCpuPrivate->FirstFreeToken = GetFirstNode 
+ (&gSmmCpuPrivate->TokenList);
 }
 
 /**
@@ -1060,23 +1065,21 @@ IsTokenInUse (
 /**
   Allocate buffer for the SPIN_LOCK and PROCEDURE_TOKEN.
 
+  @return First token of the token buffer.
 **/
-VOID
+LIST_ENTRY *
 AllocateTokenBuffer (
   VOID
   )
 {
   UINTN               SpinLockSize;
   UINT32              TokenCountPerChunk;
-  UINTN               ProcTokenSize;
   UINTN               Index;
-  PROCEDURE_TOKEN     *ProcToken;
   SPIN_LOCK           *SpinLock;
   UINT8               *SpinLockBuffer;
-  UINT8               *ProcTokenBuffer;
+  PROCEDURE_TOKEN     *ProcTokens;
 
   SpinLockSize = GetSpinLockProperties ();
-  ProcTokenSize = sizeof (PROCEDURE_TOKEN);
 
   TokenCountPerChunk = FixedPcdGet32 (PcdCpuSmmMpTokenCountPerChunk);
   ASSERT (TokenCountPerChunk != 0);
@@ -1092,49 +1095,22 @@ AllocateTokenBuffer (
   SpinLockBuffer = AllocatePool (SpinLockSize * TokenCountPerChunk);
   ASSERT (SpinLockBuffer != NULL);
 
-  ProcTokenBuffer = AllocatePool (ProcTokenSize * TokenCountPerChunk);
-  ASSERT (ProcTokenBuffer != NULL);
+  ProcTokens = AllocatePool (sizeof (PROCEDURE_TOKEN) * 
+ TokenCountPerChunk);  ASSERT (ProcTokens != NULL);
 
   for (Index = 0; Index < TokenCountPerChunk; Index++) {
     SpinLock = (SPIN_LOCK *)(SpinLockBuffer + SpinLockSize * Index);
     InitializeSpinLock (SpinLock);
 
-    ProcToken = (PROCEDURE_TOKEN *)(ProcTokenBuffer + ProcTokenSize * Index);
-    ProcToken->Signature = PROCEDURE_TOKEN_SIGNATURE;
-    ProcToken->SpinLock = SpinLock;
-    ProcToken->Used = FALSE;
-    ProcToken->RunningApCount = 0;
+    ProcTokens[Index].Signature      = PROCEDURE_TOKEN_SIGNATURE;
+    ProcTokens[Index].SpinLock       = SpinLock;
+    ProcTokens[Index].Used           = FALSE;
+    ProcTokens[Index].RunningApCount = 0;
 
-    InsertTailList (&gSmmCpuPrivate->TokenList, &ProcToken->Link);
+    InsertTailList (&gSmmCpuPrivate->TokenList, 
+ &ProcTokens[Index].Link);
   }
-}
 
-/**
-  Find first free token in the allocated token list.
-
-  @retval    return the first free PROCEDURE_TOKEN.
-
-**/
-PROCEDURE_TOKEN *
-FindFirstFreeToken (
-  VOID
-  )
-{
-  LIST_ENTRY        *Link;
-  PROCEDURE_TOKEN   *ProcToken;
-
-  Link = GetFirstNode (&gSmmCpuPrivate->TokenList);
-  while (!IsNull (&gSmmCpuPrivate->TokenList, Link)) {
-    ProcToken = PROCEDURE_TOKEN_FROM_LINK (Link);
-
-    if (!ProcToken->Used) {
-      return ProcToken;
-    }
-
-    Link = GetNextNode (&gSmmCpuPrivate->TokenList, Link);
-  }
-
-  return NULL;
+  return &ProcTokens[0].Link;
 }
 
 /**
@@ -1154,12 +1130,15 @@ GetFreeToken (
 {
   PROCEDURE_TOKEN  *NewToken;
 
-  NewToken = FindFirstFreeToken ();
-  if (NewToken == NULL) {
-    AllocateTokenBuffer ();
-    NewToken = FindFirstFreeToken ();
+  //
+  // If FirstFreeToken meets the end of token list, enlarge the token list.
+  // Set FirstFreeToken to the first free token.
+  //
+  if (gSmmCpuPrivate->FirstFreeToken == &gSmmCpuPrivate->TokenList) {
+    gSmmCpuPrivate->FirstFreeToken = AllocateTokenBuffer ();
   }
-  ASSERT (NewToken != NULL);
+  NewToken = PROCEDURE_TOKEN_FROM_LINK 
+ (gSmmCpuPrivate->FirstFreeToken);  gSmmCpuPrivate->FirstFreeToken = 
+ GetNextNode (&gSmmCpuPrivate->TokenList, 
+ gSmmCpuPrivate->FirstFreeToken);
 
   NewToken->Used = TRUE;
   NewToken->RunningApCount = RunningApsCount; diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h b/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h
index fe7e8b0323..17f4bd34fa 100644
--- a/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h
+++ b/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h
@@ -1,7 +1,7 @@
 /** @file
 Agent Module to load other modules to deploy SMM Entry Vector for X86 CPU.
 
-Copyright (c) 2009 - 2019, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2009 - 2021, Intel Corporation. All rights reserved.<BR>
 Copyright (c) 2017, AMD Incorporated. All rights reserved.<BR>
 
 SPDX-License-Identifier: BSD-2-Clause-Patent @@ -255,6 +255,7 @@ typedef struct {
 
   PROCEDURE_WRAPPER               *ApWrapperFunc;
   LIST_ENTRY                      TokenList;
+  LIST_ENTRY                      *FirstFreeToken;
 } SMM_CPU_PRIVATE_DATA;
 
 extern SMM_CPU_PRIVATE_DATA  *gSmmCpuPrivate;
--
2.21.0.windows.1