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MINOR: freq_ctr: add a generic function to report the total value

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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.
This commit is contained in:
Willy Tarreau 2021-04-11 00:38:06 +02:00
parent 6eb3d37bf4
commit f3a9f8dc5a
2 changed files with 63 additions and 0 deletions
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2
include/haproxy/freq_ctr.h
View File

@ -27,6 +27,8 @@
#include <haproxy/intops.h>
#include <haproxy/time.h>
/* exported functions from freq_ctr.c */
ullong freq_ctr_total(struct freq_ctr_period *ctr, uint period, int pend);
/* Update a frequency counter by <inc> incremental units. It is automatically
* rotated if the period is over. It is important that it correctly initializes

61
src/freq_ctr.c
View File

@ -274,6 +274,67 @@ unsigned int freq_ctr_remain_period(struct freq_ctr_period *ctr, unsigned int pe
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: