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Date:      Fri, 1 Jun 2012 21:22:47 +0000 (UTC)
From:      Davide Italiano <davide@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-projects@freebsd.org
Subject:   svn commit: r236421 - projects/calloutng/sys/kern
Message-ID:  <201206012122.q51LMlh6044107@svn.freebsd.org>
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Author: davide
Date: Fri Jun  1 21:22:46 2012
New Revision: 236421
URL: http://svn.freebsd.org/changeset/base/236421

Log:
  Provide a callout_hash() private function which is equivalent to the
  get_bucket() one except than performing the division for the number of
  buckets in the wheel. Inline the two aforementioned functions in order
  to avoid the overhead due to function call.
  
  Optimize the callout_tick() code. Right now it scans the entire wheel
  only when it's needed (i.e. we wrapped around all the wheel). Otherwise
  it scans only the buckets from the last examined in previous scan to the
  one relative to present time.
  
  Discussed with:		mav [1]
  Suggested by:		mav [2]

Modified:
  projects/calloutng/sys/kern/kern_timeout.c

Modified: projects/calloutng/sys/kern/kern_timeout.c
==============================================================================
--- projects/calloutng/sys/kern/kern_timeout.c	Fri Jun  1 19:26:38 2012	(r236420)
+++ projects/calloutng/sys/kern/kern_timeout.c	Fri Jun  1 21:22:46 2012	(r236421)
@@ -261,6 +261,8 @@ callout_cpu_init(struct callout_cpu *cc)
 		c->c_flags = CALLOUT_LOCAL_ALLOC;
 		SLIST_INSERT_HEAD(&cc->cc_callfree, c, c_links.sle);
 	}
+	cc->cc_softticks.sec = 0;
+	cc->cc_softticks.frac = 0;
 }
 
 #ifdef SMP
@@ -342,16 +344,18 @@ start_softclock(void *dummy)
 
 SYSINIT(start_softclock, SI_SUB_SOFTINTR, SI_ORDER_FIRST, start_softclock, NULL);
 
-static int
-get_bucket(struct bintime *bt) 
+static inline int
+callout_hash(struct bintime *bt) 
 {
-	time_t sec;
-	uint64_t frac;
-	sec = bt->sec;
-	frac = bt->frac;
-	return (int) (((sec<<10)+(frac>>54)) & callwheelmask);
+	return (int) ((bt->sec<<10)+(bt->frac>>54));
 } 
 
+static inline int
+get_bucket(struct bintime *bt)
+{
+	return callout_hash(bt) & callwheelmask;
+}
+
 void
 callout_tick(void)
 {
@@ -359,8 +363,8 @@ callout_tick(void)
 	struct callout_cpu *cc;
 	struct callout_tailq *sc;
 	struct bintime now;
-	int need_softclock;
-	int bucket;
+	struct bintime bt;
+	int need_softclock, first, last;
 
 	/*
 	 * Process callouts at a very low cpu priority, so we don't keep the
@@ -370,8 +374,29 @@ callout_tick(void)
 	cc = CC_SELF();
 	mtx_lock_spin_flags(&cc->cc_lock, MTX_QUIET);
 	binuptime(&now);
-	for (bucket = 0; bucket < callwheelsize; ++bucket) {
-		sc = &cc->cc_callwheel[bucket];
+	/* 
+	 * Get binuptime() may be inaccurate and return time up to 1/HZ in the past. 
+	 * In order to avoid the possible loss of one or more events look back 1/HZ
+	 * in the past from the time we last checked.
+	 */	
+	FREQ2BT(hz,&bt);
+	bintime_sub(&cc->cc_softticks,&bt);
+	first = callout_hash(&cc->cc_softticks);
+	last = callout_hash(&now);
+	/* 
+	 * Check if we wrapped around the entire wheel from the last scan.
+	 * In case, we need to scan entirely the wheel for pending callouts.
+	 */
+	if (last - first >= callwheelsize) { 
+		first &= callwheelmask;
+		last = (first - 1) & callwheelmask;
+	}
+	else {
+		first &= callwheelmask;
+		last &= callwheelmask;
+	}
+	for (;;) {	
+		sc = &cc->cc_callwheel[first];
 		TAILQ_FOREACH(tmp, sc, c_links.tqe) {
 			if (bintime_cmp(&tmp->c_time,&now, <=)) {
 				TAILQ_INSERT_TAIL(cc->cc_localexp,tmp,c_staiter);
@@ -380,6 +405,9 @@ callout_tick(void)
 				need_softclock = 1;
 			}	
 		}
+		first = (first + 1) & callwheelmask;
+		if (first == last)
+			break;
 	}
 	cc->cc_softticks = now;
 	mtx_unlock_spin_flags(&cc->cc_lock, MTX_QUIET);

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