ll_prof: Reduce profiling hooks overhead from >400% to 25%.

src/log-utils.h

 // Copyright 2006-2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 136 matching lines @@
   // Whether logging is stopped (e.g. due to insufficient resources).
   bool is_stopped_;
 
   // When logging is active, either output_handle_ or output_buffer_ is used
   // to store a pointer to log destination. If logging was opened via OpenStdout
   // or OpenFile, then output_handle_ is used. If logging was opened
   // via OpenMemoryBuffer, then output_buffer_ is used.
   // mutex_ should be acquired before using output_handle_ or output_buffer_.
   FILE* output_handle_;
 
-  // Used when low-level profiling is active to save code object contents.
-  FILE* output_code_handle_;
+  // Used when low-level profiling is active.
+  FILE* ll_output_handle_;
 
   LogDynamicBuffer* output_buffer_;
 
   // Size of dynamic buffer block (and dynamic buffer initial size).
   static const int kDynamicBufferBlockSize = 65536;
 
   // Maximum size of dynamic buffer.
   static const int kMaxDynamicBufferSize = 50 * 1024 * 1024;
 
   // Message to "seal" dynamic buffer with.
@@ skipping 51 matching lines @@
   Log* log_;
   ScopedLock sl;
   int pos_;
 };
 
 #endif  // ENABLE_LOGGING_AND_PROFILING
 
 } }  // namespace v8::internal
 
 #endif  // V8_LOG_UTILS_H_