Author: ian
Date: Sat Oct 4 15:59:15 2014
New Revision: 272528
URL: https://svnweb.freebsd.org/changeset/base/272528
Log:
Make kevent(2) periodic timer events more reliably periodic. The event
callout is now scheduled using the C_ABSOLUTE flag, and the absolute time
of each event is calculated as the time the previous event was scheduled
for plus the interval. This ensures that latency in processing a given
event doesn't perturb the arrival time of any subsequent events.
Reviewed by: jhb
Modified:
head/sys/kern/kern_event.c
head/sys/sys/event.h
Modified: head/sys/kern/kern_event.c
==============================================================================
--- head/sys/kern/kern_event.c Sat Oct 4 15:42:52 2014 (r272527)
+++ head/sys/kern/kern_event.c Sat Oct 4 15:59:15 2014 (r272528)
@@ -569,9 +569,10 @@ filt_timerexpire(void *knx)
if ((kn->kn_flags & EV_ONESHOT) != EV_ONESHOT) {
calloutp = (struct callout *)kn->kn_hook;
- callout_reset_sbt_on(calloutp,
- timer2sbintime(kn->kn_sdata, kn->kn_sfflags), 0,
- filt_timerexpire, kn, PCPU_GET(cpuid), 0);
+ *kn->kn_ptr.p_nexttime += timer2sbintime(kn->kn_sdata,
+ kn->kn_sfflags);
+ callout_reset_sbt_on(calloutp, *kn->kn_ptr.p_nexttime, 0,
+ filt_timerexpire, kn, PCPU_GET(cpuid), C_ABSOLUTE);
}
}
@@ -607,11 +608,13 @@ filt_timerattach(struct knote *kn)
kn->kn_flags |= EV_CLEAR; /* automatically set */
kn->kn_status &= ~KN_DETACHED; /* knlist_add clears it */
+ kn->kn_ptr.p_nexttime = malloc(sizeof(sbintime_t), M_KQUEUE, M_WAITOK);
calloutp = malloc(sizeof(*calloutp), M_KQUEUE, M_WAITOK);
callout_init(calloutp, CALLOUT_MPSAFE);
kn->kn_hook = calloutp;
- callout_reset_sbt_on(calloutp, to, 0,
- filt_timerexpire, kn, PCPU_GET(cpuid), 0);
+ *kn->kn_ptr.p_nexttime = to + sbinuptime();
+ callout_reset_sbt_on(calloutp, *kn->kn_ptr.p_nexttime, 0,
+ filt_timerexpire, kn, PCPU_GET(cpuid), C_ABSOLUTE);
return (0);
}
@@ -625,6 +628,7 @@ filt_timerdetach(struct knote *kn)
calloutp = (struct callout *)kn->kn_hook;
callout_drain(calloutp);
free(calloutp, M_KQUEUE);
+ free(kn->kn_ptr.p_nexttime, M_KQUEUE);
old = atomic_fetch_sub_explicit(&kq_ncallouts, 1, memory_order_relaxed);
KASSERT(old > 0, ("Number of callouts cannot become negative"));
kn->kn_status |= KN_DETACHED; /* knlist_remove sets it */
Modified: head/sys/sys/event.h
==============================================================================
--- head/sys/sys/event.h Sat Oct 4 15:42:52 2014 (r272527)
+++ head/sys/sys/event.h Sat Oct 4 15:59:15 2014 (r272528)
@@ -221,6 +221,7 @@ struct knote {
struct proc *p_proc; /* proc pointer */
struct aiocblist *p_aio; /* AIO job pointer */
struct aioliojob *p_lio; /* LIO job pointer */
+ sbintime_t *p_nexttime; /* next timer event fires at */
void *p_v; /* generic other pointer */
} kn_ptr;
struct filterops *kn_fop;
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