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
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@ -25,7 +25,7 @@
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.\"
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.\"
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.\" $FreeBSD$
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.\" $FreeBSD$
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.\"
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.\"
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.Dd March 14, 2016
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.Dd December 8, 2016
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.Dt COUNTER 9
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.Dt COUNTER 9
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.Os
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.Os
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.Sh NAME
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.Sh NAME
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@ -51,6 +51,8 @@
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.Fn counter_u64_fetch "counter_u64_t c"
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.Fn counter_u64_fetch "counter_u64_t c"
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.Ft void
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.Ft void
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.Fn counter_u64_zero "counter_u64_t c"
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.Fn counter_u64_zero "counter_u64_t c"
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.Ft int64_t
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.Fn counter_ratecheck "struct counter_rate *cr" "int64_t limit"
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.In sys/sysctl.h
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.In sys/sysctl.h
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.Fn SYSCTL_COUNTER_U64 parent nbr name access ptr descr
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.Fn SYSCTL_COUNTER_U64 parent nbr name access ptr descr
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.Fn SYSCTL_ADD_COUNTER_U64 ctx parent nbr name access ptr descr
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.Fn SYSCTL_ADD_COUNTER_U64 ctx parent nbr name access ptr descr
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@ -128,6 +130,18 @@ value for any moment.
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Clear the counter
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Clear the counter
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.Fa c
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.Fa c
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and set it to zero.
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and set it to zero.
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.It Fn counter_ratecheck cr limit
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The function is a multiprocessor-friendly version of
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.Fn ppsratecheck ,
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which uses
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.Nm
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internally.
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Returns non-negative value if the rate isn't yet reached during the current
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second, and a negative value otherwise.
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If the limit was reached on previous second, but was just reset back to zero,
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then
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.Fn counter_ratecheck
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returns number of events since previous reset.
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.It Fn SYSCTL_COUNTER_U64 parent nbr name access ptr descr
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.It Fn SYSCTL_COUNTER_U64 parent nbr name access ptr descr
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Declare a static
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Declare a static
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.Xr sysctl
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.Xr sysctl
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@ -119,3 +119,57 @@ sysctl_handle_counter_u64_array(SYSCTL_HANDLER_ARGS)
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return (0);
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return (0);
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}
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}
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/*
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* MP-friendly version of ppsratecheck().
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*
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* Returns non-negative if we are in the rate, negative otherwise.
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* 0 - rate limit not reached.
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* -1 - rate limit reached.
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* >0 - rate limit was reached before, and was just reset. The return value
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* is number of events since last reset.
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*/
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int64_t
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counter_ratecheck(struct counter_rate *cr, int64_t limit)
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{
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int64_t val;
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int now;
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val = cr->cr_over;
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now = ticks;
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if (now - cr->cr_ticks >= hz) {
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/*
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* Time to clear the structure, we are in the next second.
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* First try unlocked read, and then proceed with atomic.
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*/
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if ((cr->cr_lock == 0) &&
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atomic_cmpset_int(&cr->cr_lock, 0, 1)) {
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/*
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* Check if other thread has just went through the
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* reset sequence before us.
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*/
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if (now - cr->cr_ticks >= hz) {
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val = counter_u64_fetch(cr->cr_rate);
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counter_u64_zero(cr->cr_rate);
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cr->cr_over = 0;
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cr->cr_ticks = now;
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}
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atomic_store_rel_int(&cr->cr_lock, 0);
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} else
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/*
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* We failed to lock, in this case other thread may
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* be running counter_u64_zero(), so it is not safe
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* to do an update, we skip it.
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*/
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return (val);
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}
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counter_u64_add(cr->cr_rate, 1);
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if (cr->cr_over != 0)
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return (-1);
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if (counter_u64_fetch(cr->cr_rate) > limit)
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val = cr->cr_over = -1;
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return (val);
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}
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@ -59,5 +59,18 @@ uint64_t counter_u64_fetch(counter_u64_t);
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for (int i = 0; i < (n); i++) \
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for (int i = 0; i < (n); i++) \
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counter_u64_zero((a)[i]); \
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counter_u64_zero((a)[i]); \
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} while (0)
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} while (0)
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/*
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* counter(9) based rate checking.
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*/
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struct counter_rate {
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counter_u64_t cr_rate; /* Events since last second */
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volatile int cr_lock; /* Lock to clean the struct */
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int cr_ticks; /* Ticks on last clean */
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int cr_over; /* Over limit since cr_ticks? */
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};
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int64_t counter_ratecheck(struct counter_rate *, int64_t);
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#endif /* _KERNEL */
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#endif /* _KERNEL */
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#endif /* ! __SYS_COUNTER_H__ */
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#endif /* ! __SYS_COUNTER_H__ */
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