- Set steal_thresh to log2(ncpus). This improves idle-time load balancing

   on 2cpu machines by reducing it to 1 by default.  This improves loaded
   operation on 8cpu machines by increasing it to 3 where the extra idle
   time is not as critical.

Approved by:	re

1 files changed, 6 insertions, 0 deletions

diff --git a/sys/kern/sched_ule.c b/sys/kern/sched_ule.c
index 8569bcd..a2c33dd 100644
--- a/sys/kern/sched_ule.c
+++ b/sys/kern/sched_ule.c
@@ -1328,6 +1328,12 @@ sched_initticks(void *dummy)
 		incr = 1;
 	tickincr = incr;
 #ifdef SMP
+	/*
+	 * Set steal thresh to log2(mp_ncpu) but no greater than 4.  This
+	 * prevents excess thrashing on large machines and excess idle on
+	 * smaller machines.
+	 */
+	steal_thresh = min(ffs(mp_ncpus) - 1, 4);
 	affinity = SCHED_AFFINITY_DEFAULT;
 #endif
 }