[src/trunk]: src/sys/kern Use relaxed atomics on spc_mcount.

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

details:   https://anonhg.NetBSD.org/src/rev/6f288cf117e4
branches:  trunk
changeset: 1009137:6f288cf117e4
user:      maxv <maxv%NetBSD.org@localhost>
date:      Mon Apr 13 16:09:21 2020 +0000

description:
Use relaxed atomics on spc_mcount.

diffstat:

 sys/kern/kern_runq.c |  23 ++++++++++++++---------
 1 files changed, 14 insertions(+), 9 deletions(-)

diffs (72 lines):

diff -r 4554ea6de4b5 -r 6f288cf117e4 sys/kern/kern_runq.c
--- a/sys/kern/kern_runq.c      Mon Apr 13 15:54:45 2020 +0000
+++ b/sys/kern/kern_runq.c      Mon Apr 13 16:09:21 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_runq.c,v 1.66 2020/04/13 15:54:45 maxv Exp $      */
+/*     $NetBSD: kern_runq.c,v 1.67 2020/04/13 16:09:21 maxv 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 1.66 2020/04/13 15:54:45 maxv Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_runq.c,v 1.67 2020/04/13 16:09:21 maxv Exp $");
 
 #include "opt_dtrace.h"
 
@@ -214,8 +214,10 @@
        }
        spc->spc_flags &= ~SPCF_IDLE;
        spc->spc_count++;
-       if ((l->l_pflag & LP_BOUND) == 0)
-               spc->spc_mcount++;
+       if ((l->l_pflag & LP_BOUND) == 0) {
+               atomic_store_relaxed(&spc->spc_mcount,
+                   atomic_load_relaxed(&spc->spc_mcount) + 1);
+       }
 
        /*
         * Update the value of highest priority in the runqueue,
@@ -249,8 +251,10 @@
                spc->spc_migrating = NULL;
 
        spc->spc_count--;
-       if ((l->l_pflag & LP_BOUND) == 0)
-               spc->spc_mcount--;
+       if ((l->l_pflag & LP_BOUND) == 0) {
+               atomic_store_relaxed(&spc->spc_mcount,
+                   atomic_load_relaxed(&spc->spc_mcount) - 1);
+       }
 
        q_head = sched_getrq(spc, eprio);
        TAILQ_REMOVE(q_head, l, l_runq);
@@ -641,7 +645,7 @@
        gentle = ((curspc->spc_flags & SPCF_1STCLASS) == 0 ||
            (spc->spc_flags & SPCF_1STCLASS) != 0);
 
-       if (spc->spc_mcount < (gentle ? min_catch : 1) ||
+       if (atomic_load_relaxed(&spc->spc_mcount) < (gentle ? min_catch : 1) ||
            curspc->spc_psid != spc->spc_psid) {
                spc_unlock(ci);
                return NULL;
@@ -772,7 +776,8 @@
 
        spc = &ci->ci_schedstate;
        tspc = &tci->ci_schedstate;
-       if (tspc->spc_mcount != 0 && spc->spc_psid == tspc->spc_psid) {
+       if (atomic_load_relaxed(&tspc->spc_mcount) != 0 &&
+           spc->spc_psid == tspc->spc_psid) {
                spc_dlock(ci, tci);
                l = sched_catchlwp(tci);
                spc_unlock(ci);
@@ -856,7 +861,7 @@
                        tspc = &inner->ci_schedstate;
                        if (ci == inner || ci == mci ||
                            spc->spc_psid != tspc->spc_psid ||
-                           tspc->spc_mcount < min_catch) {
+                           atomic_load_relaxed(&tspc->spc_mcount) < min_catch) {
                                continue;
                        }
                        spc_dlock(ci, inner);