From: cheloha <cheloha@openbsd.org>
Date: Tue, 11 May 2021 13:29:25 +0000 (+0000)
Subject: timeout_barrier(9), timeout_del_barrier(9): remove kernel lock
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=c34a0df36ba0cc1c1ddc1785bb2cf469469374a3;p=openbsd

timeout_barrier(9), timeout_del_barrier(9): remove kernel lock

In timeout_barrier(9) we take/release the kernel lock to ensure that the
given timeout has finished running (if it had been running at all).

This approach is inefficient.  If we put a barrier timeout on the
queue and wait for it to run in cond_wait(9) we can block instead of
spinning for the kernel lock.  We already do this for process-context
timeouts in timeout_barrier(9) anyway.

Discussed with dlg@, visa@, and mpi@.

ok dlg@
---

diff --git a/share/man/man9/timeout.9 b/share/man/man9/timeout.9
index 6706bedbdec..b2836bd5e1f 100644
--- a/share/man/man9/timeout.9
+++ b/share/man/man9/timeout.9
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: timeout.9,v 1.52 2021/04/26 20:32:30 mvs Exp $
+.\"	$OpenBSD: timeout.9,v 1.53 2021/05/11 13:29:25 cheloha Exp $
 .\"
 .\" Copyright (c) 2000 Artur Grabowski <art@openbsd.org>
 .\" All rights reserved.
@@ -23,7 +23,7 @@
 .\" OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 .\" ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: April 26 2021 $
+.Dd $Mdocdate: May 11 2021 $
 .Dt TIMEOUT_SET 9
 .Os
 .Sh NAME
@@ -194,11 +194,6 @@ but it will wait until any current execution of the timeout has completed.
 ensures that any current execution of the timeout in the argument
 .Fa to
 has completed before returning.
-If the timeout
-.Fa to
-has been initialised with
-.Fn timeout_set
-it will take the kernel lock.
 .Pp
 The
 .Fn timeout_pending
diff --git a/sys/kern/kern_timeout.c b/sys/kern/kern_timeout.c
index acf752a8381..882560f6cda 100644
--- a/sys/kern/kern_timeout.c
+++ b/sys/kern/kern_timeout.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_timeout.c,v 1.83 2021/02/08 08:18:45 mpi Exp $	*/
+/*	$OpenBSD: kern_timeout.c,v 1.84 2021/05/11 13:29:25 cheloha Exp $	*/
 /*
  * Copyright (c) 2001 Thomas Nordin <nordin@openbsd.org>
  * Copyright (c) 2000-2001 Artur Grabowski <art@openbsd.org>
@@ -172,10 +172,10 @@ void softclock_create_thread(void *);
 void softclock_process_kclock_timeout(struct timeout *, int);
 void softclock_process_tick_timeout(struct timeout *, int);
 void softclock_thread(void *);
+void timeout_barrier_timeout(void *);
 uint32_t timeout_bucket(const struct timeout *);
 uint32_t timeout_maskwheel(uint32_t, const struct timespec *);
 void timeout_run(struct timeout *);
-void timeout_proc_barrier(void *);
 
 /*
  * The first thing in a struct timeout is its struct circq, so we
@@ -490,34 +490,38 @@ timeout_del_barrier(struct timeout *to)
 void
 timeout_barrier(struct timeout *to)
 {
-	int needsproc = ISSET(to->to_flags, TIMEOUT_PROC);
+	struct timeout barrier;
+	struct cond c;
+	int procflag;
 
-	timeout_sync_order(needsproc);
+	procflag = (to->to_flags & TIMEOUT_PROC);
+	timeout_sync_order(procflag);
 
-	if (!needsproc) {
-		KERNEL_LOCK();
-		splx(splsoftclock());
-		KERNEL_UNLOCK();
-	} else {
-		struct cond c = COND_INITIALIZER();
-		struct timeout barrier;
+	timeout_set_flags(&barrier, timeout_barrier_timeout, &c, procflag);
+	barrier.to_process = curproc->p_p;
+	cond_init(&c);
 
-		timeout_set_proc(&barrier, timeout_proc_barrier, &c);
-		barrier.to_process = curproc->p_p;
+	mtx_enter(&timeout_mutex);
 
-		mtx_enter(&timeout_mutex);
-		SET(barrier.to_flags, TIMEOUT_ONQUEUE);
+	barrier.to_time = ticks;
+	SET(barrier.to_flags, TIMEOUT_ONQUEUE);
+	if (procflag)
 		CIRCQ_INSERT_TAIL(&timeout_proc, &barrier.to_list);
-		mtx_leave(&timeout_mutex);
+	else
+		CIRCQ_INSERT_TAIL(&timeout_todo, &barrier.to_list);
 
+	mtx_leave(&timeout_mutex);
+
+	if (procflag)
 		wakeup_one(&timeout_proc);
+	else
+		softintr_schedule(softclock_si);
 
-		cond_wait(&c, "tmobar");
-	}
+	cond_wait(&c, "tmobar");
 }
 
 void
-timeout_proc_barrier(void *arg)
+timeout_barrier_timeout(void *arg)
 {
 	struct cond *c = arg;