timeval: Enable caching the current time even on x86-64.

With CFM enabled on 1000 tunnels, this reduced CPU use from about 30% to
about 22%.

Bug #15171.
Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Ethan Jackson <ethan@nicira.com>

1 files changed, 6 insertions, 12 deletions

diff --git a/lib/timeval.h b/lib/timeval.h
index 5a7b6e25..d5c12f06 100644
--- a/lib/timeval.h
+++ b/lib/timeval.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008, 2009, 2010, 2011, 2012 Nicira, Inc.
+ * Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -45,18 +45,12 @@ BUILD_ASSERT_DECL(TYPE_IS_SIGNED(time_t));
  * much time will be wasted in signal handlers and calls to clock_gettime(). */
 #define TIME_UPDATE_INTERVAL 100
 
-/* True on systems (particularly x86-64 Linux) where clock_gettime() is
- * inexpensive.  On these systems, we don't bother caching the current time.
- * Instead, we consult clock_gettime() directly when needed.
- *
- * False on systems where clock_gettime() is relatively expensive.  On these
- * systems, we cache the current time and set up a periodic SIGALRM to remind
- * us to update it.
- *
- * Also false on systems (e.g. ESX) that don't support setting up timers based
- * on a monotonically increasing clock. */
+/* True on systems that support a monotonic clock.  Compared to just getting
+ * the value of a variable, clock_gettime() is somewhat expensive, even on
+ * systems that try hard to optimize it (such as x86-64 Linux), so it's
+ * worthwhile to minimize calls via caching. */
 #ifndef CACHE_TIME
-#if defined ESX || (defined __x86_64__ && defined LINUX_DATAPATH)
+#if defined ESX
 #define CACHE_TIME 0
 #else
 #define CACHE_TIME 1