- Allow static_boost to specify no boost with '0', traditional kernel

   fixed pri boost with '1' or any priority less than the current thread's
   priority with a value greater than two.  Default the boost to
   PRI_MIN_TIMESHARE to prevent regular user-space threads from starving
   threads in the kernel.  This prevents these user-threads from also
   being scheduled as if they are high fixed-priority kernel threads.
 - Restore the setting of lowpri in tdq_choose().  It has to be either here
   or in sched_switch().  I accidentally removed it from both places.

Tested by:	kris

1 files changed, 6 insertions, 2 deletions

diff --git a/sys/kern/sched_ule.c b/sys/kern/sched_ule.c
index 9b14d0d..a1c0621 100644
--- a/sys/kern/sched_ule.c
+++ b/sys/kern/sched_ule.c
@@ -182,7 +182,7 @@ static int preempt_thresh = PRI_MIN_KERN;
 #else 
 static int preempt_thresh = 0;
 #endif
-static int static_boost = 1;
+static int static_boost = PRI_MIN_TIMESHARE;
 
 /*
  * tdq - per processor runqs and statistics.  All fields are protected by the
@@ -1833,8 +1833,10 @@ sched_sleep(struct thread *td, int prio)
 	td->td_slptick = ticks;
 	if (TD_IS_SUSPENDED(td) || prio <= PSOCK)
 		td->td_flags |= TDF_CANSWAP;
-	if (static_boost && prio)
+	if (static_boost == 1 && prio)
 		sched_prio(td, prio);
+	else if (static_boost && td->td_priority > static_boost)
+		sched_prio(td, static_boost);
 }
 
 /*
@@ -2138,8 +2140,10 @@ sched_choose(void)
 	if (td) {
 		td->td_sched->ts_ltick = ticks;
 		tdq_runq_rem(tdq, td);
+		tdq->tdq_lowpri = td->td_priority;
 		return (td);
 	}
+	tdq->tdq_lowpri = PRI_MAX_IDLE;
 	return (PCPU_GET(idlethread));
 }