Author: mav
Date: Tue Mar 13 10:21:08 2012
New Revision: 232919
URL: http://svn.freebsd.org/changeset/base/232919
Log:
Add kern.eventtimer.activetick tunable/sysctl, specifying whether each
hardclock() tick should be run on every active CPU, or on only one.
On my tests, avoiding extra interrupts because of this on 8-CPU Core i7
system with HZ=10000 saves about 2% of performance. At this moment option
implemented only for global timers, as reprogramming per-CPU timers is
too expensive now to be compensated by this benefit, especially since we
still have to regularly run hardclock() on at least one active CPU to
update system uptime. For global timer it is quite trivial: timer runs
always, but we just skip IPIs to other CPUs when possible.
Option is enabled by default now, keeping previous behavior, as periodic
hardclock() calls are still used at least to implement setitimer(2) with
ITIMER_VIRTUAL and ITIMER_PROF arguments. But since default schedulers don't
depend on it since r232917, we are much more free to experiment with it.
MFC after: 1 month
Modified:
head/share/man/man4/eventtimers.4
head/sys/kern/kern_clocksource.c
Modified: head/share/man/man4/eventtimers.4
==============================================================================
--- head/share/man/man4/eventtimers.4 Tue Mar 13 10:04:13 2012
(r232918)
+++ head/share/man/man4/eventtimers.4 Tue Mar 13 10:21:08 2012
(r232919)
@@ -24,7 +24,7 @@
.\"
.\" $FreeBSD$
.\"
-.Dd September 15, 2010
+.Dd March 13, 2012
.Dt EVENTTIMERS 4
.Os
.Sh NAME
@@ -143,6 +143,12 @@ By default this options is disabled.
If chosen timer is per-CPU
and runs in periodic mode, this option has no effect - all interrupts are
always generating.
+.It Va kern.eventtimer.activetick
+makes each CPU to receive all kinds of timer interrupts when they are busy.
+Disabling it allows to skip some hardclock() calls in some cases.
+By default this options is enabled.
+If chosen timer is per-CPU, this option has no effect - all interrupts are
+always generating, as timer reprogramming is too expensive for that case.
.El
.Sh SEE ALSO
.Xr apic 4 ,
Modified: head/sys/kern/kern_clocksource.c
==============================================================================
--- head/sys/kern/kern_clocksource.c Tue Mar 13 10:04:13 2012
(r232918)
+++ head/sys/kern/kern_clocksource.c Tue Mar 13 10:21:08 2012
(r232919)
@@ -1,5 +1,5 @@
/*-
- * Copyright (c) 2010 Alexander Motin <m...@freebsd.org>
+ * Copyright (c) 2010-2012 Alexander Motin <m...@freebsd.org>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
@@ -99,6 +99,7 @@ static struct bintime hardperiod; /* har
static struct bintime statperiod; /* statclock() events period. */
static struct bintime profperiod; /* profclock() events period. */
static struct bintime nexttick; /* Next global timer tick time. */
+static struct bintime nexthard; /* Next global hardlock() event. */
static u_int busy = 0; /* Reconfiguration is in progress. */
static int profiling = 0; /* Profiling events enabled. */
@@ -110,11 +111,16 @@ TUNABLE_INT("kern.eventtimer.singlemul",
SYSCTL_INT(_kern_eventtimer, OID_AUTO, singlemul, CTLFLAG_RW, &singlemul,
0, "Multiplier for periodic mode");
-static u_int idletick = 0; /* Idle mode allowed. */
+static u_int idletick = 0; /* Run periodic events when idle. */
TUNABLE_INT("kern.eventtimer.idletick", &idletick);
SYSCTL_UINT(_kern_eventtimer, OID_AUTO, idletick, CTLFLAG_RW, &idletick,
0, "Run periodic events when idle");
+static u_int activetick = 1; /* Run all periodic events when active.
*/
+TUNABLE_INT("kern.eventtimer.activetick", &activetick);
+SYSCTL_UINT(_kern_eventtimer, OID_AUTO, activetick, CTLFLAG_RW, &activetick,
+ 0, "Run all periodic events when active");
+
static int periodic = 0; /* Periodic or one-shot mode. */
static int want_periodic = 0; /* What mode to prefer. */
TUNABLE_INT("kern.eventtimer.periodic", &want_periodic);
@@ -202,6 +208,9 @@ handleevents(struct bintime *now, int fa
bintime_add(&state->nexthard, &hardperiod);
runs++;
}
+ if ((timer->et_flags & ET_FLAGS_PERCPU) == 0 &&
+ bintime_cmp(&state->nexthard, &nexthard, >))
+ nexthard = state->nexthard;
if (runs && fake < 2) {
hardclock_cnt(runs, usermode);
done = 1;
@@ -263,9 +272,11 @@ getnextcpuevent(struct bintime *event, i
int skip;
state = DPCPU_PTR(timerstate);
+ /* Handle hardclock() events. */
*event = state->nexthard;
- if (idle) { /* If CPU is idle - ask callouts for how long. */
- skip = 4;
+ if (idle || (!activetick && !profiling &&
+ (timer->et_flags & ET_FLAGS_PERCPU) == 0)) {
+ skip = idle ? 4 : (stathz / 2);
if (curcpu == CPU_FIRST() && tc_min_ticktock_freq > skip)
skip = tc_min_ticktock_freq;
skip = callout_tickstofirst(hz / skip) - 1;
@@ -273,7 +284,8 @@ getnextcpuevent(struct bintime *event, i
tmp = hardperiod;
bintime_mul(&tmp, skip);
bintime_add(event, &tmp);
- } else { /* If CPU is active - handle all types of events. */
+ }
+ if (!idle) { /* If CPU is active - handle other types of events. */
if (bintime_cmp(event, &state->nextstat, >))
*event = state->nextstat;
if (profiling && bintime_cmp(event, &state->nextprof, >))
@@ -295,24 +307,28 @@ getnextevent(struct bintime *event)
#ifdef SMP
int cpu;
#endif
- int c;
+ int c, nonidle;
state = DPCPU_PTR(timerstate);
*event = state->nextevent;
c = curcpu;
-#ifdef SMP
+ nonidle = !state->idle;
if ((timer->et_flags & ET_FLAGS_PERCPU) == 0) {
+#ifdef SMP
CPU_FOREACH(cpu) {
if (curcpu == cpu)
continue;
state = DPCPU_ID_PTR(cpu, timerstate);
+ nonidle += !state->idle;
if (bintime_cmp(event, &state->nextevent, >)) {
*event = state->nextevent;
c = cpu;
}
}
- }
#endif
+ if (nonidle != 0 && bintime_cmp(event, &nexthard, >))
+ *event = nexthard;
+ }
CTR5(KTR_SPARE2, "next at %d: next %d.%08x%08x by %d",
curcpu, event->sec, (unsigned int)(event->frac >> 32),
(unsigned int)(event->frac & 0xffffffff), c);
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