Changeset 87750 in vbox for trunk/src/VBox/VMM/VMMAll

Timestamp:

Feb 13, 2021 3:37:09 AM (4 years ago)

Author:

vboxsync

Message:

VMM/TM: Further relax memory ordering when signaling update-in-progress in both TMNotifyEndOfExecution and TMNotifyEndOfHalt by ensuring only the EMT writes to the memory. bugref:9941

File:

• trunk/src/VBox/VMM/VMMAll/TMAll.cpp (modified) (2 diffs)

trunk/src/VBox/VMM/VMMAll/TMAll.cpp

@@ -210 +210 @@
      * Update the data.
      *
-     * Note! Using ASMAtomicUoIncU32 instead of ASMAtomicIncU32 here to
-     *       save a tiny bit of time here.  Currently, the only user
-     *       is tmR3CpuLoadTimer(), so nothing terribly important.
+     * Note! We're not using strict memory ordering here to speed things us.
+     *       The data is in a single cache line and this thread is the only
+     *       one writing to that line, so I cannot quite imagine why we would
+     *       need any strict ordering here.
      */
     uint64_t const cNsExecutingNew = pVCpu->tm.s.cNsExecuting + cNsExecutingDelta;
     uint32_t uGen = ASMAtomicUoIncU32(&pVCpu->tm.s.uTimesGen); Assert(uGen & 1);
+    ASMCompilerBarrier();
     pVCpu->tm.s.fExecuting   = false;
     pVCpu->tm.s.cNsExecuting = cNsExecutingNew;
     pVCpu->tm.s.cPeriodsExecuting++;
-    ASMAtomicWriteU32(&pVCpu->tm.s.uTimesGen, (uGen | 1) + 1);
+    ASMCompilerBarrier();
+    ASMAtomicUoWriteU32(&pVCpu->tm.s.uTimesGen, (uGen | 1) + 1);
 
     /*
@@ -309 +312 @@
     uint64_t const cNsOtherNew    = cNsTotalNew - pVCpu->tm.s.cNsExecuting - cNsHaltedNew;
 
-    uint32_t uGen = ASMAtomicIncU32(&pVCpu->tm.s.uTimesGen); Assert(uGen & 1);
+    uint32_t uGen = ASMAtomicUoIncU32(&pVCpu->tm.s.uTimesGen); Assert(uGen & 1);
+    ASMCompilerBarrier();
     pVCpu->tm.s.fHalting     = false;
     pVCpu->tm.s.fUpdateStats = false;
     pVCpu->tm.s.cNsHalted    = cNsHaltedNew;
     pVCpu->tm.s.cPeriodsHalted++;
-    ASMAtomicWriteU32(&pVCpu->tm.s.uTimesGen, (uGen | 1) + 1);
+    ASMCompilerBarrier();
+    ASMAtomicUoWriteU32(&pVCpu->tm.s.uTimesGen, (uGen | 1) + 1);
 
 # if defined(VBOX_WITH_STATISTICS) || defined(VBOX_WITH_NS_ACCOUNTING_STATS)