Expose TimeTrace::Buffer::BUFFER_SIZE_EXP as a preprocessor macro

Users can configure the buffer size at compile-time by typing
    make MACROS=-DTIMETRACE_BUFFER_SIZE_EXP=17

Author: yilongli

Makefile

@@ -7,8 +7,8 @@ SRC_DIR = src
 WRAPPER_DIR = cwrapper
 INCLUDE_DIR = $(DESTDIR)/include
 LIB_DIR = $(DESTDIR)/lib
-CXXFLAGS=-O3 -DNDEBUG -fPIC -std=c++11 -pthread
-CFLAGS=-O3 -DNDEBUG -fPIC -std=gnu99
+CXXFLAGS = $(MACROS) -O3 -DNDEBUG -fPIC -std=c++11 -pthread
+CFLAGS = $(MACROS) -O3 -DNDEBUG -fPIC -std=gnu99
 INCLUDE=-I$(SRC_DIR)
 
 # Stuff needed for make check

src/TimeTrace.cc

@@ -337,8 +337,8 @@ TimeTrace::printInternal(std::vector<TimeTrace::Buffer*>* buffers, string* s) {
             // by the sheer size of the cycle counter.
             char message[200];
             snprintf(message, sizeof(message),
-                     "CYCLES_PER_SECOND %f\nSTART_CYCLES %lu\n",
-                     Cycles::perSecond(), startTime);
+                     "CYCLES_PER_SECOND %f\nSTART_CYCLES %lu\nBUFFER_SIZE %u\n",
+                     Cycles::perSecond(), startTime, Buffer::BUFFER_SIZE);
             if (s != NULL) {
                 s->append(message);
             } else {

src/TimeTrace.h

@@ -24,6 +24,10 @@
 #include "Atomic.h"
 #include "Cycles.h"
 
+#ifndef TIMETRACE_BUFFER_SIZE_EXP
+#define TIMETRACE_BUFFER_SIZE_EXP 13
+#endif
+
 namespace PerfUtils {
 
 // A macro to disallow the copy constructor and operator= functions
@@ -173,7 +177,7 @@ class TimeTrace {
 
       protected:
         // Determines the number of events we can retain as an exponent of 2
-        static const uint8_t BUFFER_SIZE_EXP = 13;
+        static const uint8_t BUFFER_SIZE_EXP = TIMETRACE_BUFFER_SIZE_EXP;
 
         // Total number of events that we can retain any given time.
         static const uint32_t BUFFER_SIZE = 1 << BUFFER_SIZE_EXP;