From 8d466dd80c156a33c508154f83e1907ef7087e5c Mon Sep 17 00:00:00 2001
From: cheloha <cheloha@openbsd.org>
Date: Fri, 11 Jun 2021 16:36:34 +0000
Subject: [PATCH] setitimer(2): don't round up it_value

We can reduce latency for the first expiration of a timer if we don't
round it_value up to the minimum interval (1 tick).

While we're at it, we may as well consolidate all input validation and
adjustment into a single itimerfix() call.  There are no other callers
in the kernel (nor should there be), so remove the prototype from
sys/time.h.

Discussion: https://marc.info/?l=openbsd-tech&m=162084338005502&w=2

Tested by weerd@ and claudio@.

probably ok claudio@
---
 sys/kern/kern_time.c | 40 ++++++++++++++++++++++++++--------------
 sys/sys/time.h       |  3 +--
 2 files changed, 27 insertions(+), 16 deletions(-)

diff --git a/sys/kern/kern_time.c b/sys/kern/kern_time.c
index 37771cc02f0..7a6febf4fb7 100644
--- a/sys/kern/kern_time.c
+++ b/sys/kern/kern_time.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_time.c,v 1.152 2021/05/31 12:45:33 visa Exp $	*/
+/*	$OpenBSD: kern_time.c,v 1.153 2021/06/11 16:36:34 cheloha Exp $	*/
 /*	$NetBSD: kern_time.c,v 1.20 1996/02/18 11:57:06 fvdl Exp $	*/
 
 /*
@@ -52,6 +52,8 @@
 
 #include <dev/clock_subr.h>
 
+int itimerfix(struct itimerval *);
+
 /* 
  * Time of day and interval timer support.
  *
@@ -628,10 +630,9 @@ sys_setitimer(struct proc *p, void *v, register_t *retval)
 		error = copyin(SCARG(uap, itv), &aitv, sizeof(aitv));
 		if (error)
 			return error;
-		if (itimerfix(&aitv.it_value) || itimerfix(&aitv.it_interval))
-			return EINVAL;
-		if (!timerisset(&aitv.it_value))
-			timerclear(&aitv.it_interval);
+		error = itimerfix(&aitv);
+		if (error)
+			return error;
 		newitvp = &aitv;
 	}
 	if (SCARG(uap, oitv) != NULL) {
@@ -701,21 +702,32 @@ out:
 }
 
 /*
- * Check that a proposed value to load into the .it_value or
- * .it_interval part of an interval timer is acceptable.
+ * Check if the given setitimer(2) input is valid.  Clear it_interval
+ * if it_value is unset.  Round it_interval up to the minimum interval
+ * if necessary.
  */
 int
-itimerfix(struct timeval *tv)
+itimerfix(struct itimerval *itv)
 {
+	struct timeval min_interval = { .tv_sec = 0, .tv_usec = tick };
 
-	if (tv->tv_sec < 0 || tv->tv_sec > 100000000 ||
-	    tv->tv_usec < 0 || tv->tv_usec >= 1000000)
-		return (EINVAL);
+	if (itv->it_value.tv_sec < 0 || !timerisvalid(&itv->it_value))
+		return EINVAL;
+	if (itv->it_value.tv_sec > 100000000)
+		return EINVAL;
+	if (itv->it_interval.tv_sec < 0 || !timerisvalid(&itv->it_interval))
+		return EINVAL;
+	if (itv->it_interval.tv_sec > 100000000)
+		return EINVAL;
 
-	if (tv->tv_sec == 0 && tv->tv_usec != 0 && tv->tv_usec < tick)
-		tv->tv_usec = tick;
+	if (!timerisset(&itv->it_value))
+		timerclear(&itv->it_interval);
+	if (timerisset(&itv->it_interval)) {
+		if (timercmp(&itv->it_interval, &min_interval, <))
+			itv->it_interval = min_interval;
+	}
 
-	return (0);
+	return 0;
 }
 
 /*
diff --git a/sys/sys/time.h b/sys/sys/time.h
index e5cd4eba727..019ea8153ea 100644
--- a/sys/sys/time.h
+++ b/sys/sys/time.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: time.h,v 1.58 2021/01/13 16:28:50 cheloha Exp $	*/
+/*	$OpenBSD: time.h,v 1.59 2021/06/11 16:36:34 cheloha Exp $	*/
 /*	$NetBSD: time.h,v 1.18 1996/04/23 10:29:33 mycroft Exp $	*/
 
 /*
@@ -307,7 +307,6 @@ struct proc;
 int	clock_gettime(struct proc *, clockid_t, struct timespec *);
 
 void	cancel_all_itimers(void);
-int	itimerfix(struct timeval *);
 int	itimerdecr(struct itimerspec *, long);
 int	settime(const struct timespec *);
 int	ratecheck(struct timeval *, const struct timeval *);
-- 
2.20.1