From: adash <adash>
Date: Wed, 26 Aug 2009 01:01:13 +0000 (+0000)
Subject: estimate thread context switching overhead
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=1a5e09926aff44e7c6e6de1a9581f196229c1f32;p=IRC.git

estimate thread context switching overhead
---

diff --git a/Robust/src/Benchmarks/SingleTM/MicroBenchmarks/checkContextSwitch.c b/Robust/src/Benchmarks/SingleTM/MicroBenchmarks/checkContextSwitch.c
new file mode 100644
index 00000000..9b56d750
--- /dev/null
+++ b/Robust/src/Benchmarks/SingleTM/MicroBenchmarks/checkContextSwitch.c
@@ -0,0 +1,84 @@
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <pthread.h>
+#include <sys/time.h>
+
+uint32_t COUNTER;
+pthread_mutex_t LOCK;
+pthread_mutex_t START;
+pthread_cond_t CONDITION;
+
+void * threads (
+    void * unused
+    ) {
+  // Wait till we may fire away
+  pthread_mutex_lock(&START);
+  pthread_mutex_unlock(&START);
+
+  pthread_mutex_lock(&LOCK);
+  // If I'm not the first thread, the other thread is already waiting on
+  // the condition, thus Ihave to wake it up first, otherwise we'll deadlock
+  if (COUNTER > 0) {
+    pthread_cond_signal(&CONDITION);
+  }
+  for (;;) {
+    COUNTER++;
+    pthread_cond_wait(&CONDITION, &LOCK);
+    // Always wake up the other thread before processing. The other
+    // thread will not be able to do anything as long as I don't go
+    // back to sleep first.
+    pthread_cond_signal(&CONDITION);
+  }
+  pthread_mutex_unlock(&LOCK);
+}
+
+int64_t timeInMS ()
+{
+  struct timeval t;
+
+  gettimeofday(&t, NULL);
+  return (
+      (int64_t)t.tv_sec * 1000 +
+      (int64_t)t.tv_usec / 1000
+      );
+}
+
+
+int main (
+    int argc,
+    char ** argv
+    ) {
+  int64_t start;
+  pthread_t t1;
+  pthread_t t2;
+  int64_t myTime;
+
+  pthread_mutex_init(&LOCK, NULL);
+  pthread_mutex_init(&START, NULL);   
+  pthread_cond_init(&CONDITION, NULL);
+
+  pthread_mutex_lock(&START);
+  COUNTER = 0;
+  pthread_create(&t1, NULL, threads, NULL);
+  pthread_create(&t2, NULL, threads, NULL);
+  pthread_detach(t1);
+  pthread_detach(t2);
+  // Get start time and fire away
+  myTime = timeInMS();
+  pthread_mutex_unlock(&START);
+  // Wait for about a second
+  sleep(1);
+  // Stop both threads
+  pthread_mutex_lock(&LOCK);
+  // Find out how much time has really passed. sleep won't guarantee me that
+  // I sleep exactly one second, I might sleep longer since even after being
+  // woken up, it can take some time before I gain back CPU time. Further
+  // some more time might have passed before I obtained the lock!
+  myTime = timeInMS() - myTime;
+  // Correct the number of thread switches accordingly
+  COUNTER = (uint32_t)(((uint64_t)COUNTER * 1000) / myTime);
+  printf("Number of thread switches in about one second was %u\n", COUNTER);
+  return 0;
+}
+