MINOR: freq_ctr: add a generic function to report the total value
Most of the functions designed to read a counter over a period go through
the same complex loop and only differ in the way they use the returned
values, so it was worth implementing all this into freq_ctr_total() which
returns the total number of events over a period so that the caller can
finish its operation using a divide or a remaining time calculation. As
a special case, read_freq_ctr_period() doesn't take pending events but
requires to enable an anti-flapping correction at very low frequencies.
Thus the function implements it when pend<0.
Thanks to this function it will be possible to reimplement the other ones
as inline and merge the per-second ones with the arbitrary period ones
without always adding the cost of a 64 bit divide.
diff --git a/src/freq_ctr.c b/src/freq_ctr.c
index 42fbc1c..76a8ec1 100644
--- a/src/freq_ctr.c
+++ b/src/freq_ctr.c
@@ -274,6 +274,67 @@
return freq;
}
+/* Returns the total number of events over the current + last period, including
+ * a number of already pending events <pend>. The average frequency will be
+ * obtained by dividing the output by <period>. This is essentially made to
+ * ease implementation of higher-level read functions.
+ *
+ * As a special case, if pend < 0, it's assumed there are no pending
+ * events and a flapping correction must be applied at the end. This is used by
+ * read_freq_ctr_period() to avoid reporting ups and downs on low-frequency
+ * events when the past value is <= 1.
+ */
+ullong freq_ctr_total(struct freq_ctr_period *ctr, uint period, int pend)
+{
+ ullong curr, past;
+ uint curr_tick;
+ int remain;
+
+ for (;; __ha_cpu_relax()) {
+ curr = ctr->curr_ctr;
+ past = ctr->prev_ctr;
+ curr_tick = ctr->curr_tick;
+
+ /* now let's make sure the second loads retrieve the most
+ * up-to-date values. If no value changed after a load barrier,
+ * we're certain the values we got were stable.
+ */
+ __ha_barrier_load();
+
+ if (curr_tick & 0x1)
+ continue;
+
+ if (curr != ctr->curr_ctr)
+ continue;
+
+ if (past != ctr->prev_ctr)
+ continue;
+
+ if (curr_tick != ctr->curr_tick)
+ continue;
+ break;
+ };
+
+ remain = curr_tick + period - global_now_ms;
+ if (unlikely(remain < 0)) {
+ /* We're past the first period, check if we can still report a
+ * part of last period or if we're too far away.
+ */
+ remain += period;
+ past = (remain >= 0) ? curr : 0;
+ curr = 0;
+ }
+
+ if (pend < 0) {
+ /* enable flapping correction at very low rates */
+ pend = 0;
+ if (!curr && past <= 1)
+ return past * period;
+ }
+
+ /* compute the total number of confirmed events over the period */
+ return past * remain + (curr + pend) * period;
+}
/*
* Local variables: