From: Scott Cheloha <scottcheloha@gmail.com>
Subject: Re: kernel: disable hardclock() on secondary CPUs
To: tech@openbsd.org
Date: Mon, 12 Feb 2024 11:35:20 -0600

On Fri, Feb 09, 2024 at 11:57:00AM -0600, Scott Cheloha wrote:
> Now that the dt(4) probe entry points are out of the hardclock() we
> can disable it on secondary CPUs.  There is no useful work left for
> them to do there.
> 
> This can wait a few days, just in case we need to back out the dt(4)
> change.
> 
> Thoughts?

Ping.

Index: kern_clockintr.c
===================================================================
RCS file: /cvs/src/sys/kern/kern_clockintr.c,v
diff -u -p -r1.66 kern_clockintr.c
--- kern_clockintr.c	9 Feb 2024 16:52:58 -0000	1.66
+++ kern_clockintr.c	12 Feb 2024 17:35:03 -0000
@@ -63,7 +63,7 @@ clockintr_cpu_init(const struct intrcloc
 		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 intrcloc
 			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);
 	}
 
 	/*
Index: kern_clock.c
===================================================================
RCS file: /cvs/src/sys/kern/kern_clock.c,v
diff -u -p -r1.122 kern_clock.c
--- kern_clock.c	9 Feb 2024 17:42:18 -0000	1.122
+++ kern_clock.c	12 Feb 2024 17:35:03 -0000
@@ -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++;