- Make callout(9) tickless, relying on eventtimers(4) as backend for

precise time event generation. This greatly improves granularity of
callouts which are not anymore constrained to wait next tick to be
scheduled.
- Extend the callout KPI introducing a set of callout_reset_sbt* functions,
which take a sbintime_t as timeout argument. The new KPI also offers a
way for consumers to specify precision tolerance they allow, so that
callout can coalesce events and reduce number of interrupts as well as
potentially avoid scheduling a SWI thread.
- Introduce support for dispatching callouts directly from hardware
interrupt context, specifying an additional flag. This feature should be
used carefully, as long as interrupt context has some limitations
(e.g. no sleeping locks can be held).
- Enhance mechanisms to gather informations about callwheel, introducing
a new sysctl to obtain stats.

This change breaks the KBI. struct callout fields has been changed, in
particular 'int ticks' (4 bytes) has been replaced with 'sbintime_t'
(8 bytes) and another 'sbintime_t' field was added for precision.

Together with:	mav
Reviewed by:	attilio, bde, luigi, phk
Sponsored by:	Google Summer of Code 2012, iXsystems inc.
Tested by:	flo (amd64, sparc64), marius (sparc64), ian (arm),
		markj (amd64), mav, Fabian Keil

1 files changed, 6 insertions, 2 deletions

diff --git a/sys/kern/subr_param.c b/sys/kern/subr_param.c
index f36c769..0a3580b 100644
--- a/sys/kern/subr_param.c
+++ b/sys/kern/subr_param.c
@@ -81,8 +81,10 @@ __FBSDID("$FreeBSD$");
 
 static int sysctl_kern_vm_guest(SYSCTL_HANDLER_ARGS);
 
-int	hz;
-int	tick;
+int	hz;				/* system clock's frequency */
+int	tick;				/* usec per tick (1000000 / hz) */
+struct bintime tick_bt;			/* bintime per tick (1s / hz) */
+sbintime_t tick_sbt;
 int	maxusers;			/* base tunable */
 int	maxproc;			/* maximum # of processes */
 int	maxprocperuid;			/* max # of procs per user */
@@ -221,6 +223,8 @@ init_param1(void)
 	if (hz == -1)
 		hz = vm_guest > VM_GUEST_NO ? HZ_VM : HZ;
 	tick = 1000000 / hz;
+	tick_sbt = SBT_1S / hz;
+	tick_bt = sbttobt(tick_sbt);
 
 #ifdef VM_SWZONE_SIZE_MAX
 	maxswzone = VM_SWZONE_SIZE_MAX;