Time the tests more accurately.

Instead of just using XSync, which flushes X command processing but not GPU
rendering, read back a pixel when the test is done.  Compute the actual elapsed
time instead of the SIGALRM time, because very slow rendering requests may take
a long time to finish after they've been queued by the X server.

1 files changed, 24 insertions, 7 deletions

diff --git a/utils.c b/utils.c
index b0198bd..7f71f0e 100644
--- a/utils.c
+++ b/utils.c
@@ -34,7 +34,6 @@ get_time(void)
 }
 
 static int keep_running = 0;
-static int frame_cnt = 0;
 
 void
 time_test(char *description, void (*func) (int op, XRenderSurf *src, XRenderSurf *mask, XRenderSurf *dst),
@@ -42,6 +41,10 @@ time_test(char *description, void (*func) (int op, XRenderSurf *src, XRenderSurf
 {
     char buf[51];
     struct itimerval t;
+    int frame_cnt = 0;
+    double elapsed_time;
+    struct timeval start, end;
+    XImage *img;
     snprintf(buf, 50, "%s%s", description, FILLER);
 
     t.it_interval.tv_sec = 0;
@@ -51,13 +54,31 @@ time_test(char *description, void (*func) (int op, XRenderSurf *src, XRenderSurf
 
     printf("\t\t %s", buf);
     fflush(NULL);
-    setitimer(ITIMER_REAL, &t, NULL);
     keep_running = 1;
+    setitimer(ITIMER_REAL, &t, NULL);
+
+    gettimeofday(&start, NULL);
+
     while (keep_running) {
         func(op->op, src, mask, dst);
-        XSync(disp, 0);
         ++frame_cnt;
+        // Avoid queuing up way too many X requests in case rendering is really
+        // slow.  Otherwise, we could overshoot the target time significantly.
+        if (frame_cnt % 50 == 0)
+            XSync(disp, 0);
     }
+
+    // Read back a pixel to flush any queued GPU rendering.
+    img = XGetImage(disp, src->draw, 0, 0, 1, 1, AllPlanes, ZPixmap);
+
+    gettimeofday(&end, NULL);
+
+    XDestroyImage(img);
+
+    elapsed_time = end.tv_sec - start.tv_sec + (end.tv_usec / 1000000.0 - start.tv_usec / 1000000.0);
+
+    printf ("%d frames in %g seconds = %.3f FPS\n", frame_cnt, elapsed_time,
+            frame_cnt / elapsed_time);
 }
 
 void
@@ -123,10 +144,6 @@ setup_window(void)
 void alarmhandler(int sig)
 {
     if (sig == SIGALRM) {
-        printf ("%d frames in %g seconds = %.3f FPS\n", frame_cnt, test_time,
-                frame_cnt / test_time);
-        frame_cnt    = 0;
         keep_running = 0;
     }
-    signal(SIGALRM, alarmhandler);
 }