Changeset 90665 in vbox

Timestamp:

Aug 12, 2021 2:29:37 PM (4 years ago)

Author:

vboxsync

svn:sync-xref-src-repo-rev:

146277

Message:

VMM/PDMCritSectRwEnterExcl: Tiny optimization. bugref:6695

File:

• trunk/src/VBox/VMM/VMMAll/PDMAllCritSectRw.cpp (modified) (7 diffs)

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

@@ -827 +827 @@
  * gotten exclusive ownership of the critical section.
  */
-DECLINLINE(int) pdmCritSectRwEnterExclFirst(PPDMCRITSECTRW pThis, PCRTLOCKVALSRCPOS pSrcPos, bool fNoVal, RTTHREAD hThreadSelf)
+DECL_FORCE_INLINE(int) pdmCritSectRwEnterExclFirst(PPDMCRITSECTRW pThis, PCRTLOCKVALSRCPOS pSrcPos,
+                                                   bool fNoVal, RTTHREAD hThreadSelf)
 {
     RT_NOREF(hThreadSelf, fNoVal, pSrcPos);
@@ -1071 +1072 @@
 
     /*
-     * Get cracking.
-     */
-    uint64_t u64State    = PDMCRITSECTRW_READ_STATE(&pThis->s.Core.u.s.u64State);
+     * First we try grab an idle critical section using 128-bit atomics.
+     */
+    /** @todo This could be moved up before the recursion check. */
+    uint64_t u64State = PDMCRITSECTRW_READ_STATE(&pThis->s.Core.u.s.u64State);
+#ifdef RTASM_HAVE_CMP_WRITE_U128
+    if (   (u64State & ~RTCSRW_DIR_MASK) == 0
+        && pdmCritSectRwIsCmpWriteU128Supported())
+    {
+        RTCRITSECTRWSTATE OldState;
+        OldState.s.u64State      = u64State;
+        OldState.s.hNativeWriter = NIL_RTNATIVETHREAD;
+        AssertCompile(sizeof(OldState.s.hNativeWriter) == sizeof(OldState.u128.s.Lo));
+
+        RTCRITSECTRWSTATE NewState;
+        NewState.s.u64State      = (UINT64_C(1) << RTCSRW_CNT_WR_SHIFT) | (RTCSRW_DIR_WRITE << RTCSRW_DIR_SHIFT);
+        NewState.s.hNativeWriter = hNativeSelf;
+
+        if (ASMAtomicCmpWriteU128U(&pThis->s.Core.u.u128, NewState.u128, OldState.u128))
+            return pdmCritSectRwEnterExclFirst(pThis, pSrcPos, fNoVal, hThreadSelf);
+
+        u64State = PDMCRITSECTRW_READ_STATE(&pThis->s.Core.u.s.u64State);
+    }
+#endif
+
+    /*
+     * Do it step by step.  Update the state to reflect our desire.
+     */
     uint64_t u64OldState = u64State;
 
@@ -1386 +1411 @@
     AssertReturn(hNativeSelf == hNativeWriter, VERR_NOT_OWNER);
 
+
     /*
      * Unwind one recursion. Not the last?
@@ -1410 +1436 @@
     }
 
+
     /*
      * Final recursion.
@@ -1424 +1451 @@
     }
 #endif
+
 
 #ifdef RTASM_HAVE_CMP_WRITE_U128
@@ -1456 +1484 @@
         }
     }
-#endif
+#endif /* RTASM_HAVE_CMP_WRITE_U128 */
+
 
 #if defined(IN_RING3) || defined(IN_RING0)
@@ -1566 +1595 @@
 #endif /* IN_RING3 || IN_RING0 */
 
+
 #ifndef IN_RING3
     /*