Some minor tunings/cleanups inspired by bde@ after previous commits:

 - remove extra dynamic variable initializations;
 - restore (4BSD) and implement (ULE) hogticks variable setting;
 - make sched_rr_interval() more tolerant to options;
 - restore (4BSD) and implement (ULE) kern.sched.quantum sysctl, a more
user-friendly wrapper for sched_slice;
 - tune some sysctl descriptions;
 - make some style fixes.

1 files changed, 40 insertions, 30 deletions

diff --git a/sys/kern/sched_ule.c b/sys/kern/sched_ule.c
index 719592a..5d5e908 100644
--- a/sys/kern/sched_ule.c
+++ b/sys/kern/sched_ule.c
@@ -201,9 +201,9 @@ static struct td_sched td_sched0;
  * preempt_thresh:	Priority threshold for preemption and remote IPIs.
  */
 static int sched_interact = SCHED_INTERACT_THRESH;
-static int realstathz;
-static int tickincr;
-static int sched_slice = 1;
+static int realstathz = 127;
+static int tickincr = 8 << SCHED_TICK_SHIFT;;
+static int sched_slice = 12;
 #ifdef PREEMPTION
 #ifdef FULL_PREEMPTION
 static int preempt_thresh = PRI_MAX_IDLE;
@@ -1363,13 +1363,6 @@ sched_setup(void *dummy)
 #else
 	tdq_setup(tdq);
 #endif
-	/*
-	 * To avoid divide-by-zero, we set realstathz a dummy value
-	 * in case which sched_clock() called before sched_initticks().
-	 */
-	realstathz = hz;
-	sched_slice = (realstathz/10);	/* ~100ms */
-	tickincr = 1 << SCHED_TICK_SHIFT;
 
 	/* Add thread0's load since it's running. */
 	TDQ_LOCK(tdq);
@@ -1380,7 +1373,7 @@ sched_setup(void *dummy)
 }
 
 /*
- * This routine determines the tickincr after stathz and hz are setup.
+ * This routine determines time constants after stathz and hz are setup.
  */
 /* ARGSUSED */
 static void
@@ -1389,7 +1382,8 @@ sched_initticks(void *dummy)
 	int incr;
 
 	realstathz = stathz ? stathz : hz;
-	sched_slice = (realstathz/10);	/* ~100ms */
+	sched_slice = realstathz / 10;	/* ~100ms */
+	hogticks = max(1, 2 * hz * sched_slice / realstathz);
 
 	/*
 	 * tickincr is shifted out by 10 to avoid rounding errors due to
@@ -1606,8 +1600,8 @@ int
 sched_rr_interval(void)
 {
 
-	/* Convert sched_slice to hz */
-	return (hz/(realstathz/sched_slice));
+	/* Convert sched_slice from stathz to hz. */
+	return (max(1, (sched_slice * hz + realstathz / 2) / realstathz));
 }
 
 /*
@@ -2231,16 +2225,15 @@ sched_clock(struct thread *td)
 		sched_interact_update(td);
 		sched_priority(td);
 	}
+
 	/*
-	 * We used up one time slice.
-	 */
-	if (--ts->ts_slice > 0)
-		return;
-	/*
-	 * We're out of time, force a requeue at userret().
+	 * Force a context switch if the current thread has used up a full
+	 * time slice (default is 100ms).
 	 */
-	ts->ts_slice = sched_slice;
-	td->td_flags |= TDF_NEEDRESCHED | TDF_SLICEEND;
+	if (!TD_IS_IDLETHREAD(td) && --ts->ts_slice <= 0) {
+		ts->ts_slice = sched_slice;
+		td->td_flags |= TDF_NEEDRESCHED | TDF_SLICEEND;
+	}
 }
 
 /*
@@ -2795,11 +2788,31 @@ sysctl_kern_sched_topology_spec(SYSCTL_HANDLER_ARGS)
 
 #endif
 
+static int
+sysctl_kern_quantum(SYSCTL_HANDLER_ARGS)
+{
+	int error, new_val, period;
+
+	period = 1000000 / realstathz;
+	new_val = period * sched_slice;
+	error = sysctl_handle_int(oidp, &new_val, 0, req);
+        if (error != 0 || req->newptr == NULL)
+		return (error);
+	if (new_val <= 0)
+		return (EINVAL);
+	sched_slice = max(1, (new_val + period / 2) / period);
+	hogticks = max(1, 2 * hz * sched_slice / realstathz);
+	return (0);
+}
+
 SYSCTL_NODE(_kern, OID_AUTO, sched, CTLFLAG_RW, 0, "Scheduler");
 SYSCTL_STRING(_kern_sched, OID_AUTO, name, CTLFLAG_RD, "ULE", 0,
     "Scheduler name");
+SYSCTL_PROC(_kern_sched, OID_AUTO, quantum, CTLTYPE_INT | CTLFLAG_RW,
+    NULL, 0, sysctl_kern_quantum, "I",
+    "Length of time granted to timeshare threads in microseconds");
 SYSCTL_INT(_kern_sched, OID_AUTO, slice, CTLFLAG_RW, &sched_slice, 0,
-    "Slice size for timeshare threads");
+    "Length of time granted to timeshare threads in stathz ticks");
 SYSCTL_INT(_kern_sched, OID_AUTO, interact, CTLFLAG_RW, &sched_interact, 0,
      "Interactivity score threshold");
 SYSCTL_INT(_kern_sched, OID_AUTO, preempt_thresh, CTLFLAG_RW, &preempt_thresh,
@@ -2807,9 +2820,9 @@ SYSCTL_INT(_kern_sched, OID_AUTO, preempt_thresh, CTLFLAG_RW, &preempt_thresh,
 SYSCTL_INT(_kern_sched, OID_AUTO, static_boost, CTLFLAG_RW, &static_boost,
      0,"Controls whether static kernel priorities are assigned to sleeping threads.");
 SYSCTL_INT(_kern_sched, OID_AUTO, idlespins, CTLFLAG_RW, &sched_idlespins,
-     0,"Number of times idle will spin waiting for new work.");
+     0,"Number of times idle thread will spin waiting for new work.");
 SYSCTL_INT(_kern_sched, OID_AUTO, idlespinthresh, CTLFLAG_RW, &sched_idlespinthresh,
-     0,"Threshold before we will permit idle spinning.");
+     0,"Threshold before we will permit idle thread spinning.");
 #ifdef SMP
 SYSCTL_INT(_kern_sched, OID_AUTO, affinity, CTLFLAG_RW, &affinity, 0,
     "Number of hz ticks to keep thread affinity for");
@@ -2817,17 +2830,14 @@ SYSCTL_INT(_kern_sched, OID_AUTO, balance, CTLFLAG_RW, &rebalance, 0,
     "Enables the long-term load balancer");
 SYSCTL_INT(_kern_sched, OID_AUTO, balance_interval, CTLFLAG_RW,
     &balance_interval, 0,
-    "Average frequency in stathz ticks to run the long-term balancer");
+    "Average period in stathz ticks to run the long-term balancer");
 SYSCTL_INT(_kern_sched, OID_AUTO, steal_idle, CTLFLAG_RW, &steal_idle, 0,
     "Attempts to steal work from other cores before idling");
 SYSCTL_INT(_kern_sched, OID_AUTO, steal_thresh, CTLFLAG_RW, &steal_thresh, 0,
     "Minimum load on remote cpu before we'll steal");
-
-/* Retrieve SMP topology */
 SYSCTL_PROC(_kern_sched, OID_AUTO, topology_spec, CTLTYPE_STRING |
-    CTLFLAG_RD, NULL, 0, sysctl_kern_sched_topology_spec, "A", 
+    CTLFLAG_RD, NULL, 0, sysctl_kern_sched_topology_spec, "A",
     "XML dump of detected CPU topology");
-
 #endif
 
 /* ps compat.  All cpu percentages from ULE are weighted. */