- 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, 20 insertions, 4 deletions

diff --git a/sys/sys/callout.h b/sys/sys/callout.h
index 95b9a32..7a4dec9 100644
--- a/sys/sys/callout.h
+++ b/sys/sys/callout.h
@@ -47,6 +47,16 @@
 #define	CALLOUT_RETURNUNLOCKED	0x0010 /* handler returns with mtx unlocked */
 #define	CALLOUT_SHAREDLOCK	0x0020 /* callout lock held in shared mode */
 #define	CALLOUT_DFRMIGRATION	0x0040 /* callout in deferred migration mode */
+#define	CALLOUT_PROCESSED	0x0080 /* callout in wheel or processing list? */
+#define	CALLOUT_DIRECT 		0x0100 /* allow exec from hw int context */
+
+#define	C_DIRECT_EXEC		0x0001 /* direct execution of callout */
+#define	C_PRELBITS		7
+#define	C_PRELRANGE		((1 << C_PRELBITS) - 1)
+#define	C_PREL(x)		(((x) + 1) << 1)
+#define	C_PRELGET(x)		(int)((((x) >> 1) & C_PRELRANGE) - 1)
+#define	C_HARDCLOCK		0x0100 /* align to hardclock() calls */
+#define	C_ABSOLUTE		0x0200 /* event time is absolute. */
 
 struct callout_handle {
 	struct callout *callout;
@@ -67,7 +77,15 @@ void	_callout_init_lock(struct callout *, struct lock_object *, int);
 	_callout_init_lock((c), ((rw) != NULL) ? &(rw)->lock_object :	\
 	   NULL, (flags))
 #define	callout_pending(c)	((c)->c_flags & CALLOUT_PENDING)
-int	callout_reset_on(struct callout *, int, void (*)(void *), void *, int);
+int	callout_reset_sbt_on(struct callout *, sbintime_t, sbintime_t,
+	    void (*)(void *), void *, int, int);
+#define	callout_reset_sbt(c, sbt, pr, fn, arg, flags)			\
+    callout_reset_sbt_on((c), (sbt), (pr), (fn), (arg), (c)->c_cpu, flags)
+#define	callout_reset_sbt_curcpu(c, sbt, pr, fn, arg, flags)		\
+    callout_reset_sbt_on((c), (sbt), (pr), (fn), (arg), PCPU_GET(cpuid), flags)
+#define	callout_reset_on(c, to_ticks, fn, arg, cpu)			\
+    callout_reset_sbt_on((c), (tick_sbt * (to_ticks)), 0, (fn), (arg), \
+        (cpu), C_HARDCLOCK)
 #define	callout_reset(c, on_tick, fn, arg)				\
     callout_reset_on((c), (on_tick), (fn), (arg), (c)->c_cpu)
 #define	callout_reset_curcpu(c, on_tick, fn, arg)			\
@@ -78,9 +96,7 @@ int	callout_schedule_on(struct callout *, int, int);
     callout_schedule_on((c), (on_tick), PCPU_GET(cpuid))
 #define	callout_stop(c)		_callout_stop_safe(c, 0)
 int	_callout_stop_safe(struct callout *, int);
-void	callout_tick(void);
-int	callout_tickstofirst(int limit);
-extern void (*callout_new_inserted)(int cpu, int ticks);
+void	callout_process(sbintime_t now);
 
 #endif