a scheduler benchmark that is simpler to analyze

58a15f25 · Silas Boyd-Wickizer · 94a5fb99 · 58a15f25
--- a/bin/schedbench.cc
+++ b/bin/schedbench.cc
@@ -8,43 +8,50 @@

 static volatile std::atomic<u64> waiting;
 static volatile std::atomic<u64> waking;
-static volatile u64 ftx;
 static int iters;
 static int nworkers;

+static struct {
+  u64 mem;
+  __padout__;
+} ftx[256] __mpalign__;
+
 static
-void* worker(void* x)
+void* worker0(void* x)
 {
+  // Ping pong a futex between a pair of workers
+  u64 id = (u64)x;
+  u64* f = &(ftx[id>>1].mem);
  long r;
-  int i;

-  for (i = 0; i < iters; i++) {
-    ++waiting;
-    r = futex((u64*)&ftx, FUTEX_WAIT, (u64)i, 0);
-    if (r < 0 && r != -EWOULDBLOCK)
-      die("FUTEX_WAIT: %d", r);
-    while (waking.load() == 1)
-      nop_pause();
+  if (id & 0x1) {
+    for (u64 i = 0; i < iters; i++) {
+      r = futex(f, FUTEX_WAIT, (u64)(i<<1), 0);
+      if (r < 0 && r != -EWOULDBLOCK)
+        die("futex: %d", r);
+      *f = (i<<1)+2;
+      r = futex(f, FUTEX_WAKE, 1, 0);
+      assert(r == 0);
+    }
+  } else {
+    for (u64 i = 0; i < iters; i++) {
+      *f = (i<<1)+1;
+      r = futex(f, FUTEX_WAKE, 1, 0);
+      assert(r == 0);
+      r = futex(f, FUTEX_WAIT, (u64)(i<<1)+1, 0);
+      if (r < 0 && r != -EWOULDBLOCK)
+        die("futex: %d", r);
+    }
  }

  return nullptr;
 }

 static
-void master(void)
+void master0(void)
 {
-  long r;
-
-  for (int i = 0; i < iters; i++) {
-    while (waiting.load() < (i+1)*nworkers)
-      nop_pause();
-    
-    waking.store(1);
-    ftx = i+1;
-    r = futex((u64*)&ftx, FUTEX_WAKE, nworkers, 0);  
-    assert(r == 0);
-    waking.store(0);
-  }
+  for (int i = 0; i < nworkers; i++)
+    wait();
 }

 int
@@ -54,7 +61,7 @@ main(int ac, char** av)

  if (ac < 3)
    die("usage: %s iters nworkers", av[0]);
-  ftx = 0;
+
  iters = atoi(av[1]);
  nworkers = atoi(av[2]);
  waiting.store(0);
@@ -62,17 +69,53 @@ main(int ac, char** av)
  for (int i = 0; i < nworkers; i++) {
    pthread_t th;

-    r = pthread_create(&th, nullptr, worker, nullptr);
+    r = pthread_create(&th, nullptr, worker0, (void*)(u64)i);
    if (r < 0)
      die("pthread_create");
  }
  nsleep(1000*1000);

  u64 t0 = rdtsc();
-  master();
+  master0();
  u64 t1 = rdtsc();
  printf("%lu\n", (t1-t0)/iters);
-  
-  for (int i = 0; i < nworkers; i++)
-    wait();
 }
+
+#if 0
+static volatile u64 ftx;
+
+static
+void* worker0(void* x)
+{
+  long r;
+  int i;
+
+  for (i = 0; i < iters; i++) {
+    ++waiting;
+    r = futex((u64*)&ftx, FUTEX_WAIT, (u64)i, 0);
+    if (r < 0 && r != -EWOULDBLOCK)
+      die("FUTEX_WAIT: %d", r);
+    while (waking.load() == 1)
+      nop_pause();
+  }
+
+  return nullptr;
+}
+
+static
+void master0(void)
+{
+  long r;
+
+  for (int i = 0; i < iters; i++) {
+    while (waiting.load() < (i+1)*nworkers)
+      nop_pause();
+    
+    waking.store(1);
+    ftx = i+1;
+    r = futex((u64*)&ftx, FUTEX_WAKE, nworkers, 0);  
+    assert(r == 0);
+    waking.store(0);
+  }
+}
+#endif