erts, kernel: Add os:perf_counter function

The perf_counter is a very very cheap and high resolution timer
that can be used to timestamp system events. It does not have
monoticity guarantees, but should on most OS's expose a monotonous
time.

A special instruction has been created for this counter to further
speed up fetching it.

OTP-12908

1 files changed, 74 insertions, 2 deletions

diff --git a/erts/emulator/beam/erl_time_sup.c b/erts/emulator/beam/erl_time_sup.c
index 668dbb5daa..6509c6a805 100644
--- a/erts/emulator/beam/erl_time_sup.c
+++ b/erts/emulator/beam/erl_time_sup.c
@@ -1749,7 +1749,7 @@ erts_get_monotonic_time(ErtsSchedulerData *esdp)
 {
     ErtsMonotonicTime mtime = time_sup.r.o.get_time();
     update_last_mtime(esdp, mtime);
-    return mtime;    
+    return mtime;
 }
 
 ErtsMonotonicTime
@@ -2435,9 +2435,81 @@ BIF_RETTYPE os_system_time_0(BIF_ALIST_0)
     BIF_RET(make_time_val(BIF_P, stime));
 }
 
-BIF_RETTYPE os_system_time_1(BIF_ALIST_0)
+BIF_RETTYPE os_system_time_1(BIF_ALIST_1)
 {
     ErtsSystemTime stime = erts_os_system_time();
     BIF_RET(time_unit_conversion(BIF_P, BIF_ARG_1, stime, 0));
 }
 
+BIF_RETTYPE
+os_perf_counter_0(BIF_ALIST_0)
+{
+    ErtsSysHrTime pcounter;
+    sys_perf_counter(&pcounter);
+    BIF_RET(make_time_val(BIF_P, pcounter));
+}
+
+BIF_RETTYPE erts_internal_perf_counter_unit_0(BIF_ALIST_0)
+{
+    BIF_RET(make_time_val(BIF_P, SYS_PERF_COUNTER_UNIT));
+}
+
+/* What resolution to spin to in micro seconds */
+#define RESOLUTION 100
+/* How many iterations to spin */
+#define ITERATIONS 1
+/* How many significant figures to round to */
+#define SIGFIGS 3
+
+static ErtsSysHrTime perf_counter_unit = 0;
+
+static ErtsSysHrTime erts_calculate_perf_counter_unit(void);
+static ErtsSysHrTime erts_calculate_perf_counter_unit() {
+    int i;
+    ErtsSysHrTime pre, post;
+    double value = 0;
+    double round_factor;
+#if defined(HAVE_GETHRTIME) && defined(GETHRTIME_WITH_CLOCK_GETTIME)
+    struct timespec basetime,comparetime;
+#define __GETTIME(arg) clock_gettime(CLOCK_MONOTONIC,arg)
+#define __GETUSEC(arg) (arg.tv_nsec / 1000)
+#else
+    SysTimeval basetime,comparetime;
+#define __GETTIME(arg) sys_gettimeofday(arg)
+#define __GETUSEC(arg) arg.tv_usec
+#endif
+
+    for (i = 0; i < ITERATIONS; i++) {
+        /* Make sure usec just flipped over at current resolution */
+        __GETTIME(&basetime);
+        do {
+            __GETTIME(&comparetime);
+        } while ((__GETUSEC(basetime) / RESOLUTION) == (__GETUSEC(comparetime) / RESOLUTION));
+
+        sys_perf_counter(&pre);
+
+        __GETTIME(&basetime);
+        do {
+            __GETTIME(&comparetime);
+        } while ((__GETUSEC(basetime) / RESOLUTION) == (__GETUSEC(comparetime) / RESOLUTION));
+
+        sys_perf_counter(&post);
+
+        value += post - pre;
+    }
+    /* After this value is ticks per us */
+    value /= (RESOLUTION*ITERATIONS);
+
+    /* We round to 3 significant figures */
+    round_factor = pow(10.0, SIGFIGS - ceil(log10(value)));
+    value = ((ErtsSysHrTime)(value * round_factor + 0.5)) / round_factor;
+
+    /* convert to ticks per second */
+    return 1000000 * value;
+}
+
+ErtsSysHrTime erts_perf_counter_unit() {
+    if (perf_counter_unit == 0)
+        perf_counter_unit = erts_calculate_perf_counter_unit();
+    return perf_counter_unit;
+}