From 29a69d5a1b7aa8b6759284fe8ee2cf0854b71157 Mon Sep 17 00:00:00 2001
From: Thomas Haller <thaller@redhat.com>
Date: Tue, 5 Mar 2024 09:53:03 +0100
Subject: [PATCH] tests/performance: add "factor" argument to performance test

By default, the test estimates a run factor for each test. This means,
if you run performance under `perf`, the results are not comparable,
as the run time depends on the estimated factor.

Add an option, to set a fixed factor.

Of course, there is only one factor argument for all tests.  Quite
possibly, you would want to run each test individually with a factor
appropriate for the test. On the other hand, all tests should be tuned
so that the same factor gives a similar test duration. So this may not
be a concern, or the tests should be adjusted. In any case, the option
is most useful when running only one test explicitly.

You can get a suitable factor by running the test once with "--verbose".

Another use case is if you run the benchmark under valgrind. Valgrind
slows down the run so much, that the estimated factor would be quite
off. As a result, the chosen code paths are different from the real run.
By setting the factor, the timing measurements don't affect the executed
code.
---
 gobject/tests/performance/performance.c | 51 ++++++++++++++++++-------
 1 file changed, 37 insertions(+), 14 deletions(-)

diff --git a/gobject/tests/performance/performance.c b/gobject/tests/performance/performance.c
index c584f99ed..fdbd2c316 100644
--- a/gobject/tests/performance/performance.c
+++ b/gobject/tests/performance/performance.c
@@ -33,6 +33,7 @@
 static gboolean verbose = FALSE;
 static gboolean quiet = FALSE;
 static int test_length = DEFAULT_TEST_TIME;
+static double test_factor = 0;
 
 static GOptionEntry cmd_entries[] = {
   {"verbose", 'v', 0, G_OPTION_ARG_NONE, &verbose,
@@ -41,6 +42,8 @@ static GOptionEntry cmd_entries[] = {
    "Print extra information", NULL},
   {"seconds", 's', 0, G_OPTION_ARG_INT, &test_length,
    "Time to run each test in seconds", NULL},
+  {"factor", 'f', 0, G_OPTION_ARG_DOUBLE, &test_factor,
+   "Use a fixed factor for sample runs (also $GLIB_PERFORMANCE_FACTOR)", NULL},
   G_OPTION_ENTRY_NULL
 };
 
@@ -101,24 +104,32 @@ run_test (PerformanceTest *test)
       g_print ("Estimating round time\n");
     }
 
-  /* Estimate time for one run by doing a few test rounds */
   min_elapsed = 0;
-  for (i = 0; i < ESTIMATE_ROUND_TIME_N_RUNS; i++)
+
+  if (test_factor > 0)
     {
-      test->init (test, data, 1.0);
-      g_timer_start (timer);
-      test->run (test, data);
-      g_timer_stop (timer);
-      test->finish (test, data);
-
-      elapsed = g_timer_elapsed (timer, NULL);
-      if (i == 0)
-	min_elapsed = elapsed;
-      else
-	min_elapsed = MIN (min_elapsed, elapsed);
+      factor = test_factor;
     }
+  else
+    {
+      /* Estimate time for one run by doing a few test rounds. */
+      for (i = 0; i < ESTIMATE_ROUND_TIME_N_RUNS; i++)
+        {
+          test->init (test, data, 1.0);
+          g_timer_start (timer);
+          test->run (test, data);
+          g_timer_stop (timer);
+          test->finish (test, data);
 
-  factor = TARGET_ROUND_TIME / min_elapsed;
+          elapsed = g_timer_elapsed (timer, NULL);
+          if (i == 0)
+            min_elapsed = elapsed;
+          else
+            min_elapsed = MIN (min_elapsed, elapsed);
+        }
+
+      factor = TARGET_ROUND_TIME / min_elapsed;
+    }
 
   if (verbose)
     g_print ("Uncorrected round time: %.4f msecs, correction factor %.2f\n", 1000*min_elapsed, factor);
@@ -1550,8 +1561,14 @@ main (int   argc,
   PerformanceTest *test;
   GOptionContext *context;
   GError *error = NULL;
+  const char *str;
   int i;
 
+  if ((str = g_getenv ("GLIB_PERFORMANCE_FACTOR")) && str[0])
+    {
+      test_factor = g_strtod (str, NULL);
+    }
+
   context = g_option_context_new ("GObject performance tests");
   g_option_context_add_main_entries (context, cmd_entries, NULL);
   if (!g_option_context_parse (context, &argc, &argv, &error))
@@ -1560,6 +1577,12 @@ main (int   argc,
       return 1;
     }
 
+  if (test_factor < 0)
+    {
+      g_printerr ("%s: test factor must be positive\n", argv[0]);
+      return 1;
+    }
+
   if (argc > 1)
     {
       for (i = 1; i < argc; i++)