[src/trunk]: src/sys/kern Take some pressure from vdrain lock:

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

details:   https://anonhg.NetBSD.org/src/rev/d121d016dc63
branches:  trunk
changeset: 1009279:d121d016dc63
user:      hannken <hannken%NetBSD.org@localhost>
date:      Sun Apr 19 13:25:00 2020 +0000

description:
Take some pressure from vdrain lock:

- Use cv_signal() instead of cv_broadcast(), there is only one waiter.
- No need to signal if number of vnodes doesn't increase.
- Use kpause(1) instead of yield().

diffstat:

 sys/kern/vfs_vnode.c |  13 ++++++-------
 1 files changed, 6 insertions(+), 7 deletions(-)

diffs (41 lines):

diff -r f539c8723318 -r d121d016dc63 sys/kern/vfs_vnode.c
--- a/sys/kern/vfs_vnode.c      Sun Apr 19 13:22:58 2020 +0000
+++ b/sys/kern/vfs_vnode.c      Sun Apr 19 13:25:00 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vfs_vnode.c,v 1.120 2020/04/13 19:23:18 ad Exp $       */
+/*     $NetBSD: vfs_vnode.c,v 1.121 2020/04/19 13:25:00 hannken Exp $  */
 
 /*-
  * Copyright (c) 1997-2011, 2019, 2020 The NetBSD Foundation, Inc.
@@ -155,7 +155,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_vnode.c,v 1.120 2020/04/13 19:23:18 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_vnode.c,v 1.121 2020/04/19 13:25:00 hannken Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_pax.h"
@@ -519,8 +519,9 @@
                 */
                numvnodes += d;
        }
-       if (numvnodes > desiredvnodes || listhd == &lru_list[LRU_VRELE])
-               cv_broadcast(&vdrain_cv);
+       if ((d > 0 && numvnodes > desiredvnodes) ||
+           listhd == &lru_list[LRU_VRELE])
+               cv_signal(&vdrain_cv);
        mutex_exit(&vdrain_lock);
 }
 
@@ -686,9 +687,7 @@
                }
 
                if (vdrain_retry) {
-                       mutex_exit(&vdrain_lock);
-                       yield();
-                       mutex_enter(&vdrain_lock);
+                       kpause("vdrainrt", false, 1, &vdrain_lock);
                } else {
                        vdrain_gen++;
                        cv_broadcast(&vdrain_gen_cv);