Check sleep timeout state only if the sleep has a timeout. Otherwise,

the timeout cancellation in sleep_finish_timeout() would acquire the
kernel lock every time in the no-timeout case, as noticed by mpi@.

This also reduces the contention of timeout_mutex.

OK mpi@, feedback guenther@

1 files changed, 18 insertions, 10 deletions

diff --git a/sys/kern/kern_synch.c b/sys/kern/kern_synch.c
index 1aa80d925e9..6b858a8c727 100644
--- a/sys/kern/kern_synch.c
+++ b/sys/kern/kern_synch.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_synch.c,v 1.153 2019/10/15 10:05:43 mpi Exp $	*/
+/*	$OpenBSD: kern_synch.c,v 1.154 2019/11/12 04:20:21 visa Exp $	*/
 /*	$NetBSD: kern_synch.c,v 1.37 1996/04/22 01:38:37 christos Exp $	*/
 
 /*
@@ -345,6 +345,7 @@ sleep_setup(struct sleep_state *sls, const volatile void *ident, int prio,
 	sls->sls_catch = 0;
 	sls->sls_do_sleep = 1;
 	sls->sls_sig = 1;
+	sls->sls_timeout = 0;
 
 	SCHED_LOCK(sls->sls_s);
 
@@ -387,8 +388,13 @@ sleep_finish(struct sleep_state *sls, int do_sleep)
 void
 sleep_setup_timeout(struct sleep_state *sls, int timo)
 {
-	if (timo)
-		timeout_add(&curproc->p_sleep_to, timo);
+	struct proc *p = curproc;
+
+	if (timo) {
+		KASSERT((p->p_flag & P_TIMEOUT) == 0);
+		sls->sls_timeout = 1;
+		timeout_add(&p->p_sleep_to, timo);
+	}
 }
 
 int
@@ -396,13 +402,15 @@ sleep_finish_timeout(struct sleep_state *sls)
 {
 	struct proc *p = curproc;
 
-	if (p->p_flag & P_TIMEOUT) {
-		atomic_clearbits_int(&p->p_flag, P_TIMEOUT);
-		return (EWOULDBLOCK);
-	} else {
-		/* This must not sleep. */
-		timeout_del_barrier(&p->p_sleep_to);
-		KASSERT((p->p_flag & P_TIMEOUT) == 0);
+	if (sls->sls_timeout) {
+		if (p->p_flag & P_TIMEOUT) {
+			atomic_clearbits_int(&p->p_flag, P_TIMEOUT);
+			return (EWOULDBLOCK);
+		} else {
+			/* This must not sleep. */
+			timeout_del_barrier(&p->p_sleep_to);
+			KASSERT((p->p_flag & P_TIMEOUT) == 0);
+		}
 	}
 
 	return (0);