Author: glebius
Date: Fri Dec 9 17:58:34 2016
New Revision: 309745
URL: https://svnweb.freebsd.org/changeset/base/309745
Log:
Provide counter_ratecheck(), a MP-friendly substitution to ppsratecheck().
When rated event happens at a very quick rate, the ppsratecheck() is not
only racy, but also becomes a performance bottleneck.
Together with: rrs, jtl
Modified:
head/share/man/man9/counter.9
head/sys/kern/subr_counter.c
head/sys/sys/counter.h
Modified: head/share/man/man9/counter.9
==============================================================================
--- head/share/man/man9/counter.9 Fri Dec 9 17:58:07 2016
(r309744)
+++ head/share/man/man9/counter.9 Fri Dec 9 17:58:34 2016
(r309745)
@@ -25,7 +25,7 @@
.\"
.\" $FreeBSD$
.\"
-.Dd March 14, 2016
+.Dd December 8, 2016
.Dt COUNTER 9
.Os
.Sh NAME
@@ -51,6 +51,8 @@
.Fn counter_u64_fetch "counter_u64_t c"
.Ft void
.Fn counter_u64_zero "counter_u64_t c"
+.Ft int64_t
+.Fn counter_ratecheck "struct counter_rate *cr" "int64_t limit"
.In sys/sysctl.h
.Fn SYSCTL_COUNTER_U64 parent nbr name access ptr descr
.Fn SYSCTL_ADD_COUNTER_U64 ctx parent nbr name access ptr descr
@@ -128,6 +130,18 @@ value for any moment.
Clear the counter
.Fa c
and set it to zero.
+.It Fn counter_ratecheck cr limit
+The function is a multiprocessor-friendly version of
+.Fn ppsratecheck ,
+which uses
+.Nm
+internally.
+Returns non-negative value if the rate isn't yet reached during the current
+second, and a negative value otherwise.
+If the limit was reached on previous second, but was just reset back to zero,
+then
+.Fn counter_ratecheck
+returns number of events since previous reset.
.It Fn SYSCTL_COUNTER_U64 parent nbr name access ptr descr
Declare a static
.Xr sysctl
Modified: head/sys/kern/subr_counter.c
==============================================================================
--- head/sys/kern/subr_counter.c Fri Dec 9 17:58:07 2016
(r309744)
+++ head/sys/kern/subr_counter.c Fri Dec 9 17:58:34 2016
(r309745)
@@ -119,3 +119,57 @@ sysctl_handle_counter_u64_array(SYSCTL_H
return (0);
}
+
+/*
+ * MP-friendly version of ppsratecheck().
+ *
+ * Returns non-negative if we are in the rate, negative otherwise.
+ * 0 - rate limit not reached.
+ * -1 - rate limit reached.
+ * >0 - rate limit was reached before, and was just reset. The return value
+ * is number of events since last reset.
+ */
+int64_t
+counter_ratecheck(struct counter_rate *cr, int64_t limit)
+{
+ int64_t val;
+ int now;
+
+ val = cr->cr_over;
+ now = ticks;
+
+ if (now - cr->cr_ticks >= hz) {
+ /*
+ * Time to clear the structure, we are in the next second.
+ * First try unlocked read, and then proceed with atomic.
+ */
+ if ((cr->cr_lock == 0) &&
+ atomic_cmpset_int(&cr->cr_lock, 0, 1)) {
+ /*
+ * Check if other thread has just went through the
+ * reset sequence before us.
+ */
+ if (now - cr->cr_ticks >= hz) {
+ val = counter_u64_fetch(cr->cr_rate);
+ counter_u64_zero(cr->cr_rate);
+ cr->cr_over = 0;
+ cr->cr_ticks = now;
+ }
+ atomic_store_rel_int(&cr->cr_lock, 0);
+ } else
+ /*
+ * We failed to lock, in this case other thread may
+ * be running counter_u64_zero(), so it is not safe
+ * to do an update, we skip it.
+ */
+ return (val);
+ }
+
+ counter_u64_add(cr->cr_rate, 1);
+ if (cr->cr_over != 0)
+ return (-1);
+ if (counter_u64_fetch(cr->cr_rate) > limit)
+ val = cr->cr_over = -1;
+
+ return (val);
+}
Modified: head/sys/sys/counter.h
==============================================================================
--- head/sys/sys/counter.h Fri Dec 9 17:58:07 2016 (r309744)
+++ head/sys/sys/counter.h Fri Dec 9 17:58:34 2016 (r309745)
@@ -59,5 +59,18 @@ uint64_t counter_u64_fetch(counter_u64_t
for (int i = 0; i < (n); i++) \
counter_u64_zero((a)[i]); \
} while (0)
+
+/*
+ * counter(9) based rate checking.
+ */
+struct counter_rate {
+ counter_u64_t cr_rate; /* Events since last second */
+ volatile int cr_lock; /* Lock to clean the struct */
+ int cr_ticks; /* Ticks on last clean */
+ int cr_over; /* Over limit since cr_ticks? */
+};
+
+int64_t counter_ratecheck(struct counter_rate *, int64_t);
+
#endif /* _KERNEL */
#endif /* ! __SYS_COUNTER_H__ */
_______________________________________________
svn-src-head@freebsd.org mailing list
https://lists.freebsd.org/mailman/listinfo/svn-src-head
To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
