[src/trunk]: src/sys/sys Introduce curlwp_bind and curlwp_bindx

[ozaki-r <ozaki-r%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/65bef88184cf
branches:  trunk
changeset: 345931:65bef88184cf
user:      ozaki-r <ozaki-r%NetBSD.org@localhost>
date:      Thu Jun 16 02:34:33 2016 +0000

description:
Introduce curlwp_bind and curlwp_bindx

The API prevents the current LWP from migrating between CPUs during
the critical section (between curlwp_bind and curlwp_bindx). One use
case of it is psref(9) that has a contract that forbids such migrations.

Proposed at http://mail-index.netbsd.org/tech-kern/2016/06/13/msg020710.html
(check it out if you want to know why the function names are chosen)

diffstat:

 sys/sys/lwp.h |  24 +++++++++++++++++++++++-
 1 files changed, 23 insertions(+), 1 deletions(-)

diffs (38 lines):

diff -r b337b0fb6fbc -r 65bef88184cf sys/sys/lwp.h
--- a/sys/sys/lwp.h     Thu Jun 16 01:33:35 2016 +0000
+++ b/sys/sys/lwp.h     Thu Jun 16 02:34:33 2016 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: lwp.h,v 1.170 2015/03/31 01:10:02 matt Exp $   */
+/*     $NetBSD: lwp.h,v 1.171 2016/06/16 02:34:33 ozaki-r Exp $        */
 
 /*-
  * Copyright (c) 2001, 2006, 2007, 2008, 2009, 2010
@@ -521,6 +521,28 @@
 #define        DOPREEMPT_ACTIVE        0x01
 #define        DOPREEMPT_COUNTED       0x02
 
+/*
+ * Prevent curlwp from migrating between CPUs beteen curlwp_bind and
+ * curlwp_bindx. One use case is psref(9) that has a contract that
+ * forbids migrations.
+ */
+static inline int
+curlwp_bind(void)
+{
+       int bound;
+
+       bound = curlwp->l_pflag & LP_BOUND;
+       curlwp->l_pflag |= LP_BOUND;
+
+       return bound;
+}
+
+static inline void
+curlwp_bindx(int bound)
+{
+       curlwp->l_pflag ^= bound ^ LP_BOUND;
+}
+
 #endif /* _KERNEL */
 
 /* Flags for _lwp_create(), as per Solaris. */