[PATCH v2 2/3] UefiCpuPkg/MpInitLib: wait no longer than necessary for initial AP startup

[Laszlo Ersek <lersek@redhat.com>]

Sometimes a platform knows exactly how many CPUs it has at boot. It should
be able to
- set PcdCpuMaxLogicalProcessorNumber dynamically to this number,
- set PcdCpuApInitTimeOutInMicroSeconds to infinity (marked with 0),
- and expect that MpInitLib wait exactly as long as necessary for all APs
  to report in.

Other platforms should be able to continue setting a reasonably large
upper bound on supported CPUs, and waiting for a reasonable, fixed amount
of time for all APs to report in.

Add this functionality. The TimedWaitForApFinish() function will return
when all APs have reported in, or the timeout has expired -- whichever
happens first.

(Accessing these PCDs dynamically is safe. The PEI and DXE phase instances
of this library are restricted to PEIM and DXE_DRIVER client modules, thus
the PCD accesses cannot be linked into runtime code.)

Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Jeff Fan <jeff.fan@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Bugzilla: https://bugzilla.tianocore.org/show_bug.cgi?id=116
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
---
 UefiCpuPkg/UefiCpuPkg.dec            |  3 +-
 UefiCpuPkg/Library/MpInitLib/MpLib.c | 67 +++++++++++++++++++-
 2 files changed, 68 insertions(+), 2 deletions(-)

diff --git a/UefiCpuPkg/UefiCpuPkg.dec b/UefiCpuPkg/UefiCpuPkg.dec
index ca560398bbef..8607ae8b7ae8 100644
--- a/UefiCpuPkg/UefiCpuPkg.dec
+++ b/UefiCpuPkg/UefiCpuPkg.dec
@@ -174,7 +174,8 @@ [PcdsFixedAtBuild, PcdsPatchableInModule, PcdsDynamic, PcdsDynamicEx]
   # @Prompt Configure max supported number of Logical Processors
   gUefiCpuPkgTokenSpaceGuid.PcdCpuMaxLogicalProcessorNumber|64|UINT32|0x00000002
   ## Specifies timeout value in microseconds for the BSP to detect all APs for the first time.
-  # @Prompt Timeout for the BSP to detect all APs for the first time.
+  #  When set to zero, the BSP will wait forever for all (PcdCpuMaxLogicalProcessorNumber-1) APs to report in.
+  # @Prompt Timeout for the BSP to detect all APs for the first time (zero means await maximum supported AP count).
   gUefiCpuPkgTokenSpaceGuid.PcdCpuApInitTimeOutInMicroSeconds|50000|UINT32|0x00000004
   ## Specifies the base address of the first microcode Patch in the microcode Region.
   # @Prompt Microcode Region base address.
diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c b/UefiCpuPkg/Library/MpInitLib/MpLib.c
index 15dbfa1e7d6c..76de92fa552a 100644
--- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
+++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
@@ -684,6 +684,22 @@ FillExchangeInfoData (
 }
 
 /**
+  Helper function that waits until the finished AP count reaches the specified
+  limit, or the specified timeout elapses (whichever comes first).
+
+  @param[in] CpuMpData        Pointer to CPU MP Data.
+  @param[in] FinishedApLimit  The number of finished APs to wait for.
+  @param[in] TimeLimit        The number of microseconds to wait for. Zero
+                              means infinity.
+**/
+VOID
+TimedWaitForApFinish (
+  IN CPU_MP_DATA               *CpuMpData,
+  IN UINT32                    FinishedApLimit,
+  IN UINT32                    TimeLimit
+  );
+
+/**
   This function will be called by BSP to wakeup AP.
 
   @param[in] CpuMpData          Pointer to CPU MP Data
@@ -748,7 +764,11 @@ WakeUpAP (
       //
       // Wait for all potential APs waken up in one specified period
       //
-      MicroSecondDelay (PcdGet32(PcdCpuApInitTimeOutInMicroSeconds));
+      TimedWaitForApFinish (
+        CpuMpData,
+        PcdGet32 (PcdCpuMaxLogicalProcessorNumber) - 1,
+        PcdGet32 (PcdCpuApInitTimeOutInMicroSeconds)
+        );
     } else {
       //
       // Wait all APs waken up if this is not the 1st broadcast of SIPI
@@ -895,6 +915,51 @@ CheckTimeout (
 }
 
 /**
+  Helper function that waits until the finished AP count reaches the specified
+  limit, or the specified timeout elapses (whichever comes first).
+
+  @param[in] CpuMpData        Pointer to CPU MP Data.
+  @param[in] FinishedApLimit  The number of finished APs to wait for.
+  @param[in] TimeLimit        The number of microseconds to wait for. Zero
+                              means infinity.
+**/
+VOID
+TimedWaitForApFinish (
+  IN CPU_MP_DATA               *CpuMpData,
+  IN UINT32                    FinishedApLimit,
+  IN UINT32                    TimeLimit
+  )
+{
+  CpuMpData->TotalTime = 0;
+  CpuMpData->ExpectedTime = CalculateTimeout (
+                              TimeLimit,
+                              &CpuMpData->CurrentTime
+                              );
+  while (CpuMpData->FinishedCount < FinishedApLimit &&
+         !CheckTimeout (
+            &CpuMpData->CurrentTime,
+            &CpuMpData->TotalTime,
+            CpuMpData->ExpectedTime
+            )) {
+    CpuPause ();
+  }
+
+  if (CpuMpData->FinishedCount >= FinishedApLimit) {
+    DEBUG ((
+      DEBUG_VERBOSE,
+      "%a: reached FinishedApLimit=%u in %Lu microseconds\n",
+      __FUNCTION__,
+      FinishedApLimit,
+      DivU64x64Remainder (
+        MultU64x32 (CpuMpData->TotalTime, 1000000),
+        GetPerformanceCounterProperties (NULL, NULL),
+        NULL
+        )
+      ));
+  }
+}
+
+/**
   Reset an AP to Idle state.
 
   Any task being executed by the AP will be aborted and the AP
-- 
2.9.2