Improved support for OSX timers.

opal/mca/timer/darwin/timer_darwin.h

@@ -27,17 +27,29 @@ typedef uint64_t opal_timer_t;
 /* frequency in mhz */
 OPAL_DECLSPEC extern opal_timer_t opal_timer_darwin_freq;
 OPAL_DECLSPEC extern mach_timebase_info_data_t opal_timer_darwin_info;
+OPAL_DECLSPEC extern opal_timer_t opal_timer_darwin_bias;
 
+/**
+ * Use the pragmatic solution proposed at
+ * http://stackoverflow.com/questions/23378063/how-can-i-use-mach-absolute-time-without-overflowing/23378064#23378064
+ */
 static inline opal_timer_t
 opal_timer_base_get_cycles(void)
 {
+    uint64_t now = mach_absolute_time();
+
     if( opal_timer_darwin_info.denom == 0 ) {
         (void)mach_timebase_info(&opal_timer_darwin_info);
+        if( opal_timer_darwin_info.denom > 1024 ) {
+            double frac = (double)opal_timer_darwin_info.numer/opal_timer_darwin_info.denom;
+            opal_timer_darwin_info.denom = 1024;
+            opal_timer_darwin_info.numer = opal_timer_darwin_info.denom * frac + 0.5;
         }
-    /* this is basically a wrapper around the "right" assembly to get
-       the tick counter off the PowerPC Time Base.  I believe it's
-       something similar on x86 */
-    return mach_absolute_time() * opal_timer_darwin_info.numer / opal_timer_darwin_info.denom / 1000;
+        opal_timer_darwin_bias = now;
+    }
+    /* this is basically a wrapper around the "right" assembly to convert
+       the tick counter off the PowerPC Time Base into nanos. */
+    return (now - opal_timer_darwin_bias) * opal_timer_darwin_info.numer / opal_timer_darwin_info.denom;
 }
 
 
@@ -45,7 +57,7 @@ static inline opal_timer_t
 opal_timer_base_get_usec(void)
 {
     /* freq is in Hz, so this gives usec */
-    return mach_absolute_time() * 1000000  / opal_timer_darwin_freq;
+    return opal_timer_base_get_cycles() / 1000;
 }
 
 

opal/mca/timer/darwin/timer_darwin_component.c

@@ -26,6 +26,7 @@
 
 opal_timer_t opal_timer_darwin_freq;
 mach_timebase_info_data_t opal_timer_darwin_info = {.denom = 0};
+opal_timer_t opal_timer_darwin_bias;
 
 static int opal_timer_darwin_open(void);
 
@@ -51,13 +52,6 @@ const opal_timer_base_component_2_0_0_t mca_timer_darwin_component = {
     },
 };
 
-
-int opal_timer_darwin_open(void)
-{
-    mach_timebase_info_data_t sTBI;
-
-    mach_timebase_info(&sTBI);
-
 /* mach_timebase_info() returns a fraction that can be multiplied
    by the difference between two calls to mach_absolute_time() to
    get the number of nanoseconds that passed between the two
@@ -94,7 +88,12 @@ int opal_timer_darwin_open(void)
    1000000000 will give you a frequency in cycles / second if you
    think of mach_absolute_time() always returning a cycle count.
 */
-    opal_timer_darwin_freq = sTBI.denom * (1000000000 / sTBI.numer);
+int opal_timer_darwin_open(void)
+{
+    /* Call the opal_timer_base_get_cycles once to start the enging */
+    (void)opal_timer_base_get_cycles();
+
+    opal_timer_darwin_freq = opal_timer_darwin_info.denom * (1000000000 / opal_timer_darwin_info.numer);
 
     return OPAL_SUCCESS;
 }