From: Mark Kettenis <mark.kettenis@xs4all.nl>
Subject: Re: kernel: disable hardclock() on secondary CPUs
To: Scott Cheloha <scottcheloha@gmail.com>
Cc: tech@openbsd.org
Date: Mon, 12 Feb 2024 20:47:27 +0100

> Date: Mon, 12 Feb 2024 11:35:20 -0600
> From: Scott Cheloha <scottcheloha@gmail.com>
> 
> 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.

ok kettenis@

Does this mean that we'll start running less interrupts on secondary
CPUs now?

> 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++;
> 
>