PERFORCE change 165049 for review

[Prashant Vaibhav]

http://perforce.freebsd.org/chv.cgi?CH=165049

Change 165049 by pvaibhav at pvaibhav_matrix on 2009/06/24 14:46:44

	Some minor improvements in softclock():
	1. Use cached 'ticks' instead of cc->cc_monoticks directly. This
	   will avoid the softclock potentially running too long as it
	   chases behind monoticks, in cases where monoticks is modified
	   while softclock is still executing
	2. Check if number of callouts processed during a single invocation
	   of softclock() is more than a threshold value. If yes, temporarily
	   unlock cc_lock so interrupts can be processed. This was present in
	   the original softclock() implementation too.
	3. Corrected order of temporary unlocking and extracting first pending
	   callout -- extraction should always be done after re-acquiring the
	   cc_lock.

Affected files ...

.. //depot/projects/soc2009/calloutapi/src/sys/kern/kern_timeout.c#4 edit

Differences ...

==== //depot/projects/soc2009/calloutapi/src/sys/kern/kern_timeout.c#4 (text+ko) ====

@@ -260,7 +260,7 @@
 	 * it with cc_lock held; incorrect locking order.
 	 */
 	mtx_unlock_spin_flags(&cc->cc_lock, MTX_QUIET);
-	if (need_softclock)
+	if (need_softclock == 1)
 		swi_sched(cc->cc_cookie, 0);
 }
 
@@ -304,11 +304,11 @@
 {
 	struct callout_cpu *cc;
 	struct callout *c;
-	int curticks;
-	int depth;
+	int steps;
 	int mpcalls;
 	int lockcalls;
 	int gcalls;
+	int curticks;
 #ifdef DIAGNOSTIC
 	struct bintime bt1, bt2;
 	struct timespec ts2;
@@ -323,15 +323,24 @@
 	mpcalls = 0;
 	lockcalls = 0;
 	gcalls = 0;
-	depth = 0;
+	steps = 0;
 	cc = (struct callout_cpu *)arg;
 	CC_LOCK(cc);
 	/*
-	 * ticks may be modified by hard clock, so cache it
+	 * cc_monoticks might be modified by hardclock, so cache it
 	 */
 	curticks = cc->cc_monoticks;
 	CTR1(KTR_CALLOUT, "softclock run at %d", curticks);
 	while (!MINHEAP_EMPTY(&cc->cc_callqueue)) {
+		if (steps++ > MAX_SOFTCLOCK_STEPS) {
+			/*
+			 * Give interrupts a chance
+			 */
+			CC_UNLOCK(cc);
+			; /* nothing */
+			CC_LOCK(cc);
+			steps = 0;
+		}
 		c = MINHEAP_FIRST(&cc->cc_callqueue);
 		if (c->c_time > curticks) {
 			/*