Changeset 121511 in webkit for trunk/Source/JavaScriptCore/jit/JITStubs.cpp

Timestamp:

Jun 28, 2012, 7:40:14 PM (13 years ago)

Author:

[email protected]

Message:

DFG recompilation heuristics should be based on count, not rate
​https://bugs.webkit.org/show_bug.cgi?id=90146

Reviewed by Oliver Hunt.

This removes a bunch of code that was previously trying to prevent spurious
reoptimizations if a large enough majority of executions of a code block did
not result in OSR exit. It turns out that this code was purely harmful. This
patch removes all of that logic and replaces it with a dead-simple
heuristic: if you exit more than N times (where N is an exponential function
of the number of times the code block has already been recompiled) then we
will recompile.

This appears to be a broad ~1% win on many benchmarks large and small.

• bytecode/CodeBlock.cpp:

(JSC::CodeBlock::CodeBlock):

• bytecode/CodeBlock.h:

(JSC::CodeBlock::osrExitCounter):
(JSC::CodeBlock::countOSRExit):
(CodeBlock):
(JSC::CodeBlock::addressOfOSRExitCounter):
(JSC::CodeBlock::offsetOfOSRExitCounter):
(JSC::CodeBlock::adjustedExitCountThreshold):
(JSC::CodeBlock::exitCountThresholdForReoptimization):
(JSC::CodeBlock::exitCountThresholdForReoptimizationFromLoop):
(JSC::CodeBlock::shouldReoptimizeNow):
(JSC::CodeBlock::shouldReoptimizeFromLoopNow):

• bytecode/ExecutionCounter.cpp:

(JSC::ExecutionCounter::setThreshold):

• bytecode/ExecutionCounter.h:

(ExecutionCounter):
(JSC::ExecutionCounter::clippedThreshold):

• dfg/DFGJITCompiler.cpp:

(JSC::DFG::JITCompiler::compileBody):

• dfg/DFGOSRExit.cpp:

(JSC::DFG::OSRExit::considerAddingAsFrequentExitSiteSlow):

• dfg/DFGOSRExitCompiler.cpp:

(JSC::DFG::OSRExitCompiler::handleExitCounts):

• dfg/DFGOperations.cpp:
• jit/JITStubs.cpp:

(JSC::DEFINE_STUB_FUNCTION):

• runtime/Options.cpp:

(Options):
(JSC::Options::initializeOptions):

• runtime/Options.h:

(Options):

File:

• trunk/Source/JavaScriptCore/jit/JITStubs.cpp (modified) (4 diffs)

trunk/Source/JavaScriptCore/jit/JITStubs.cpp

@@ -1929 +1929 @@
 
 #if ENABLE(JIT_VERBOSE_OSR)
-    dataLog("%p: Entered optimize with bytecodeIndex = %u, executeCounter = %s, reoptimizationRetryCounter = %u, optimizationDelayCounter = %u\n", codeBlock, bytecodeIndex, codeBlock->jitExecuteCounter().status(), codeBlock->reoptimizationRetryCounter(), codeBlock->optimizationDelayCounter());
+    dataLog("%p: Entered optimize with bytecodeIndex = %u, executeCounter = %s, reoptimizationRetryCounter = %u, optimizationDelayCounter = %u, exitCounter = ", codeBlock, bytecodeIndex, codeBlock->jitExecuteCounter().status(), codeBlock->reoptimizationRetryCounter(), codeBlock->optimizationDelayCounter());
+    if (codeBlock->hasOptimizedReplacement())
+        dataLog("%u", codeBlock->replacement()->osrExitCounter());
+    else
+        dataLog("N/A");
+    dataLog("\n");
 #endif
 
@@ -1939 +1944 @@
     if (codeBlock->hasOptimizedReplacement()) {
 #if ENABLE(JIT_VERBOSE_OSR)
-        dataLog("Considering OSR into %p(%p) with success/fail %u/%u.\n", codeBlock, codeBlock->replacement(), codeBlock->replacement()->speculativeSuccessCounter(), codeBlock->replacement()->speculativeFailCounter());
+        dataLog("Considering OSR into %p(%p).\n", codeBlock, codeBlock->replacement());
 #endif
+        // If we have an optimized replacement, then it must be the case that we entered
+        // cti_optimize from a loop. That's because is there's an optimized replacement,
+        // then all calls to this function will be relinked to the replacement and so
+        // the prologue OSR will never fire.
+        
+        // This is an interesting threshold check. Consider that a function OSR exits
+        // in the middle of a loop, while having a relatively low exit count. The exit
+        // will reset the execution counter to some target threshold, meaning that this
+        // code won't be reached until that loop heats up for >=1000 executions. But then
+        // we do a second check here, to see if we should either reoptimize, or just
+        // attempt OSR entry. Hence it might even be correct for
+        // shouldReoptimizeFromLoopNow() to always return true. But we make it do some
+        // additional checking anyway, to reduce the amount of recompilation thrashing.
         if (codeBlock->replacement()->shouldReoptimizeFromLoopNow()) {
 #if ENABLE(JIT_VERBOSE_OSR)
@@ -1986 +2004 @@
 
         codeBlock->optimizeSoon();
-        optimizedCodeBlock->countSpeculationSuccess();
         STUB_SET_RETURN_ADDRESS(address);
         return;
@@ -1997 +2014 @@
     // Count the OSR failure as a speculation failure. If this happens a lot, then
     // reoptimize.
-    optimizedCodeBlock->countSpeculationFailure();
+    optimizedCodeBlock->countOSRExit();
     
 #if ENABLE(JIT_VERBOSE_OSR)
-    dataLog("Encountered OSR failure into %p(%p) with success/fail %u/%u.\n", codeBlock, codeBlock->replacement(), codeBlock->replacement()->speculativeSuccessCounter(), codeBlock->replacement()->speculativeFailCounter());
+    dataLog("Encountered OSR failure into %p(%p).\n", codeBlock, codeBlock->replacement());
 #endif