From: cheloha <cheloha@openbsd.org>
Date: Mon, 12 Feb 2024 22:07:33 +0000 (+0000)
Subject: kernel: disable hardclock() on secondary CPUs
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=8434116fd2c22fec81b518e015e6bea3382f0e33;p=openbsd

kernel: disable hardclock() on secondary CPUs

There is no useful work left for secondary CPUs to do in hardclock().
Disable cq_hardclock on secondary CPUs and remove the now-unnecessary
early-return from hardclock().

This change reduces every system's normal clock interrupt rate by
(HZ - HZ/10) per secondary CPU.  For example, an 8-core machine
with a HZ=100 kernel should see its clock interrupt rate drop from
~1600 to ~960.

Thread: https://marc.info/?l=openbsd-tech&m=170750140915898&w=2

ok kettenis@
---

diff --git a/sys/kern/kern_clock.c b/sys/kern/kern_clock.c
index f6f98b7344d..f851089aaf2 100644
--- a/sys/kern/kern_clock.c
+++ b/sys/kern/kern_clock.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_clock.c,v 1.122 2024/02/09 17:42:18 cheloha Exp $	*/
+/*	$OpenBSD: kern_clock.c,v 1.123 2024/02/12 22:07:33 cheloha Exp $	*/
 /*	$NetBSD: kern_clock.c,v 1.34 1996/06/09 04:51:03 briggs Exp $	*/
 
 /*-
@@ -140,13 +140,6 @@ initclocks(void)
 void
 hardclock(struct clockframe *frame)
 {
-	/*
-	 * If we are not the primary CPU, we're not allowed to do
-	 * any more work.
-	 */
-	if (CPU_IS_PRIMARY(curcpu()) == 0)
-		return;
-
 	tc_ticktock();
 	ticks++;
 	jiffies++;
diff --git a/sys/kern/kern_clockintr.c b/sys/kern/kern_clockintr.c
index 4141a2bbeba..1a36e497531 100644
--- a/sys/kern/kern_clockintr.c
+++ b/sys/kern/kern_clockintr.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kern_clockintr.c,v 1.66 2024/02/09 16:52:58 cheloha Exp $ */
+/* $OpenBSD: kern_clockintr.c,v 1.67 2024/02/12 22:07:33 cheloha Exp $ */
 /*
  * Copyright (c) 2003 Dale Rahn <drahn@openbsd.org>
  * Copyright (c) 2020 Mark Kettenis <kettenis@openbsd.org>
@@ -63,7 +63,7 @@ clockintr_cpu_init(const struct intrclock *ic)
 		clockqueue_intrclock_install(cq, ic);
 
 	/* TODO: Remove this from struct clockintr_queue. */
-	if (cq->cq_hardclock.cl_expiration == 0) {
+	if (CPU_IS_PRIMARY(ci) && cq->cq_hardclock.cl_expiration == 0) {
 		clockintr_bind(&cq->cq_hardclock, ci, clockintr_hardclock,
 		    NULL);
 	}
@@ -99,12 +99,6 @@ clockintr_cpu_init(const struct intrclock *ic)
 			clockintr_schedule(&cq->cq_hardclock, 0);
 		else
 			clockintr_advance(&cq->cq_hardclock, hardclock_period);
-	} else {
-		if (cq->cq_hardclock.cl_expiration == 0) {
-			clockintr_stagger(&cq->cq_hardclock, hardclock_period,
-			     multiplier, MAXCPUS);
-		}
-		clockintr_advance(&cq->cq_hardclock, hardclock_period);
 	}
 
 	/*