[src/trunk]: src/sys/kern - Fix an inverted test that could have prevented LW...

[ad <ad%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/4046617ea071
branches:  trunk
changeset: 968355:4046617ea071
user:      ad <ad%NetBSD.org@localhost>
date:      Mon Jan 13 11:53:24 2020 +0000

description:
- Fix an inverted test that could have prevented LWPs running on helper
  CPUs to teleport somewhere better during preempt().

- Fix a comment.

diffstat:

 sys/kern/kern_runq.c |  34 ++++++++++++++++++++--------------
 1 files changed, 20 insertions(+), 14 deletions(-)

diffs (70 lines):

diff -r e7b62db7162e -r 4046617ea071 sys/kern/kern_runq.c
--- a/sys/kern/kern_runq.c      Mon Jan 13 11:47:06 2020 +0000
+++ b/sys/kern/kern_runq.c      Mon Jan 13 11:53:24 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_runq.c,v 1.58 2020/01/12 22:03:22 ad Exp $        */
+/*     $NetBSD: kern_runq.c,v 1.59 2020/01/13 11:53:24 ad Exp $        */
 
 /*-
  * Copyright (c) 2019, 2020 The NetBSD Foundation, Inc.
@@ -56,7 +56,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_runq.c,v 1.58 2020/01/12 22:03:22 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_runq.c,v 1.59 2020/01/13 11:53:24 ad Exp $");
 
 #include "opt_dtrace.h"
 
@@ -884,12 +884,12 @@
         * Try to select another CPU if:
         *
         * - there is no migration pending already
-        * - and there is no realtime LWP in the mix (no time to waste then)
-        * - and this LWP is running on a 2nd class CPU, or is child of vfork()
+        * - and this LWP is running on a 2nd class CPU
+        * - or this LWP is a child of vfork() that has just done execve()
         */
-       if (tspc->spc_maxpriority >= PRI_USER_RT || l->l_target_cpu != NULL ||
-           ((tspc->spc_flags & SPCF_1STCLASS) | (l->l_pflag & LP_TELEPORT))
-           == 0) {
+       if (l->l_target_cpu != NULL ||
+           ((tspc->spc_flags & SPCF_1STCLASS) != 0 &&
+           (l->l_pflag & LP_TELEPORT) == 0)) {
                return;
        }
 
@@ -911,20 +911,26 @@
                tci = tci->ci_sibling[CPUREL_CORE];
        }
 
-       /*
-        * Try to find a better CPU to take it, but don't move to another
-        * 2nd class CPU; there's not much point.
-        *
-        * Search in the current CPU package in order to try and keep L2/L3
-        * cache locality, but expand to include the whole system if needed.
-        */
        if ((l->l_pflag & LP_TELEPORT) != 0) {
+               /*
+                * A child of vfork(): now that the parent is released,
+                * scatter far and wide, to match the LSIDL distribution
+                * done in sched_takecpu().
+                */
                l->l_pflag &= ~LP_TELEPORT;
                tci = sched_bestcpu(l, sched_nextpkg());
                if (tci != ci) {
                        l->l_target_cpu = tci;
                }
        } else {
+               /*
+                * Try to find a better CPU to take it, but don't move to
+                * another 2nd class CPU; there's not much point.
+                *
+                * Search in the current CPU package in order to try and
+                * keep L2/L3 cache locality, but expand to include the
+                * whole system if needed.
+                */
                tci = sched_bestcpu(l, l->l_cpu);
                if (tci != ci &&
                    (tci->ci_schedstate.spc_flags & SPCF_1STCLASS) != 0) {