[cairo-perf] Emit warning, if cairo-perf is not CPU bound

cairo-perf and the X server should be bound to CPUs (either the same
	or separate) on SMP systems. Not doing so causes random results when
	the X server is moved to or from cairo-perf's CPU during the
	benchmarks.

configure.in

@@ -577,6 +577,17 @@ dnl Checks for precise integer types
 AC_CHECK_HEADERS([stdint.h signal.h inttypes.h sys/int_types.h])
 AC_CHECK_TYPES([uint64_t, uint128_t])
 
+dnl ===========================================================================
+dnl check for CPU affinity support
+AC_CHECK_HEADERS([sched.h], [
+  AC_CHECK_FUNCS([sched_getaffinity], [
+    AC_DEFINE([HAVE_SCHED_GETAFFINITY], [1],
+	      [Define to 1 if you have Linux compatible sched_getaffinity])
+  ])
+])
+
+dnl ===========================================================================
+dnl check compiler flags
 AC_DEFUN([CAIRO_CC_TRY_FLAG], [
   AC_MSG_CHECKING([whether $CC supports $1])
 

perf/cairo-perf.c

@@ -27,12 +27,17 @@
  */
 
 #include "cairo-perf.h"
+#include "config.h"
 
 /* For getopt */
 #include <unistd.h>
 /* For basename */
 #include <libgen.h>
 
+#ifdef HAVE_SCHED_H
+#include <sched.h>
+#endif
+
 #define CAIRO_PERF_ITERATIONS_DEFAULT	100
 #define CAIRO_PERF_LOW_STD_DEV		0.03
 #define CAIRO_PERF_STABLE_STD_DEV_COUNT	5
@@ -259,6 +264,40 @@ parse_options (cairo_perf_t *perf, int argc, char *argv[])
     }
 }
 
+static int 
+check_cpu_affinity(void)
+{
+#ifdef HAVE_SCHED_GETAFFINITY
+
+    cpu_set_t affinity;
+    int i, cpu_count;
+
+    if (sched_getaffinity(0, sizeof(affinity), &affinity)) {
+        perror("sched_getaffinity");
+        return -1;
+    }
+
+    for(i = 0, cpu_count = 0; i < CPU_SETSIZE; ++i) {
+        if (CPU_ISSET(i, &affinity))
+            ++cpu_count;
+    }
+
+    if (cpu_count > 1) {
+        fputs(
+            "WARNING: cairo-perf has not been bound to a single CPU.\n", 
+            stderr);
+        return -1;
+    }
+
+    return 0;
+#else
+    fputs(
+        "WARNING: Cannot check CPU affinity for this platform.\n", 
+        stderr);
+    return -1;
+#endif
+}
+
 int
 main (int argc, char *argv[])
 {
@@ -271,6 +310,19 @@ main (int argc, char *argv[])
 
     parse_options (&perf, argc, argv);
 
+    if (check_cpu_affinity()) {
+        fputs(
+            "NOTICE: cairo-perf and the X server should be bound to CPUs (either the same\n"
+            "or separate) on SMP systems. Not doing so causes random results when the X\n"
+            "server is moved to or from cairo-perf's CPU during the benchmarks:\n"
+            "\n"
+            "    $ sudo taskset -cp 0 $(pidof X)\n"
+            "    $ taskset -cp 1 $$\n"
+            "\n"
+            "See taskset(1) for information about changing CPU affinity.\n",
+            stderr);
+    }
+
     for (i = 0; targets[i].name; i++) {
 	perf.target = target = &targets[i];
 	perf.test_number = 0;