svn commit: r322942 - head/sys/kern

[Conrad Meyer]

Author: cem
Date: Sun Aug 27 05:14:48 2017
New Revision: 322942
URL: https://svnweb.freebsd.org/changeset/base/322942

Log:
  Improve scheduler performance
  
  Improve scheduler performance by flattening nonsensical topology layers
  (layers with only one child don't serve any purpose).
  
  This is especially relevant on non-AMD Zen systems after r322776.  On my
  dual core Intel laptop, this brings the kern.sched.topology_spec table down
  from three levels to two.
  
  Submitted by:	jeff
  Reviewed by:	attilio
  Sponsored by:	Dell EMC Isilon

Modified:
  head/sys/kern/subr_smp.c

Modified: head/sys/kern/subr_smp.c
==============================================================================
--- head/sys/kern/subr_smp.c	Sun Aug 27 03:10:16 2017	(r322941)
+++ head/sys/kern/subr_smp.c	Sun Aug 27 05:14:48 2017	(r322942)
@@ -630,6 +630,15 @@ smp_topo(void)
 		panic("Built bad topology at %p.  CPU mask (%s) != (%s)",
 		    top, cpusetobj_strprint(cpusetbuf, &top->cg_mask),
 		    cpusetobj_strprint(cpusetbuf2, &all_cpus));
+
+	/*
+	 * Collapse nonsense levels that may be created out of convenience by
+	 * the MD layers.  They cause extra work in the search functions.
+	 */
+	while (top->cg_children == 1) {
+		top = &top->cg_child[0];
+		top->cg_parent = NULL;
+	}
 	return (top);
 }