[src/trunk]: src/sys/kern Restore psz_lock just for the event count.

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

details:   https://anonhg.NetBSD.org/src/rev/5de1f593a419
branches:  trunk
changeset: 465823:5de1f593a419
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Thu Dec 05 03:21:17 2019 +0000

description:
Restore psz_lock just for the event count.

Cost of mutex_enter/exit is negligible compared to the xcall we just
did, so this is not going to meaningfully affect performance.

diffstat:

 sys/kern/subr_pserialize.c |  14 ++++++++------
 1 files changed, 8 insertions(+), 6 deletions(-)

diffs (55 lines):

diff -r 52f9b8c14f0e -r 5de1f593a419 sys/kern/subr_pserialize.c
--- a/sys/kern/subr_pserialize.c        Thu Dec 05 03:21:08 2019 +0000
+++ b/sys/kern/subr_pserialize.c        Thu Dec 05 03:21:17 2019 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: subr_pserialize.c,v 1.15 2019/12/03 13:30:52 martin Exp $      */
+/*     $NetBSD: subr_pserialize.c,v 1.16 2019/12/05 03:21:17 riastradh Exp $   */
 
 /*-
  * Copyright (c) 2010, 2011 The NetBSD Foundation, Inc.
@@ -31,13 +31,14 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: subr_pserialize.c,v 1.15 2019/12/03 13:30:52 martin Exp $");
+__KERNEL_RCSID(0, "$NetBSD: subr_pserialize.c,v 1.16 2019/12/05 03:21:17 riastradh Exp $");
 
 #include <sys/param.h>
 #include <sys/atomic.h>
 #include <sys/cpu.h>
 #include <sys/evcnt.h>
 #include <sys/kmem.h>
+#include <sys/mutex.h>
 #include <sys/pserialize.h>
 #include <sys/xcall.h>
 
@@ -45,6 +46,7 @@
        lwp_t *                 psz_owner;
 };
 
+static kmutex_t                        psz_lock        __cacheline_aligned;
 static struct evcnt            psz_ev_excl     __cacheline_aligned;
 
 /*
@@ -56,6 +58,7 @@
 pserialize_init(void)
 {
 
+       mutex_init(&psz_lock, MUTEX_DEFAULT, IPL_NONE);
        evcnt_attach_dynamic(&psz_ev_excl, EVCNT_TYPE_MISC, NULL,
            "pserialize", "exclusive access");
 }
@@ -120,10 +123,9 @@
 
        KASSERT(psz->psz_owner == curlwp);
        psz->psz_owner = NULL;
-#ifdef __HAVE_ATOMIC64_LOADSTORE
-       atomic_store_relaxed(&psz_ev_excl.ev_count,
-           1 + atomic_load_relaxed(&psz_ev_excl.ev_count));
-#endif
+       mutex_enter(&psz_lock);
+       psz_ev_excl.ev_count++;
+       mutex_exit(&psz_lock);
 }
 
 int