From: Stefan Fritsch <sf@sfritsch.de>
Subject: Re: Mostly-Inverted CPU-Core ordering
To: Stuart Henderson <stu@spacehopper.org>
Cc: Theo Buehler <tb@theobuehler.org>, Mark Kettenis <mark.kettenis@xs4all.nl>,  gsgs7878@proton.me, tech@openbsd.org, visa@openbsd.org
Date: Sat, 7 Mar 2026 09:33:49 +0100

On Fri, 6 Mar 2026, Stuart Henderson wrote:

> On 2026/03/06 09:49, Theo Buehler wrote:
> > On Wed, Jan 14, 2026 at 03:47:15PM +0100, Stefan Fritsch wrote:
> > 
> > [...]
> > 
> > > > > Updated diff below that should fix all architectures. sparc64 already has 
> > > > > the correct ordering. Boot tested on amd64, i386, arm64.
> > > > 
> > > > On arm64, the slow cores are typically (but not always) listed before
> > > > the fast cores.  Don't think that is a good reason not to change the
> > > > order of the list to be more sensible.
> > > 
> > > Does this mean that the boot cpu is then a slow core, too?
> > > 
> > > In the long term, one probably wants to have some field in cpu_info that
> > > denotes the core type and then make intrmap_create() use that info to
> > > prefer the fastest cores.
> > > 
> > > As noted by tb@, the previous diff broke !MULTIPROCESSOR configurations.
> > > New diff attached.
> > 
> > Not my area. Should this be committed?
> 
> fwiw, no change in cpu order on my m2 mini.

The change is not visible in dmesg. The cpus attach in the same 
chronological order and get the same numbers. What the patch fixes is that 
they are now put into the cpu_info_list->ci_next linked list in the right 
order, which is the order used by CPU_INFO_FOREACH.

The easiest way to observe the effect of the diff that I found is this 
additional diff:

diff --git a/sys/kern/init_main.c b/sys/kern/init_main.c
index a51ecb9a39f..e712681a333 100644
--- a/sys/kern/init_main.c
+++ b/sys/kern/init_main.c
@@ -163,6 +163,8 @@ main(void *framep)
 	struct proc *p;
 	struct process *pr;
 	struct pdevinit *pdev;
+	struct cpu_info *ci;
+	CPU_INFO_ITERATOR cii;
 	extern struct pdevinit pdevinit[];
 	extern void disk_init(void);
 
@@ -533,6 +535,9 @@ main(void *framep)
 
 	config_process_deferred_mountroot();
 
+	CPU_INFO_FOREACH(cii, ci) {
+		printf("cpu %d\n", ci->ci_cpuid);
+	}
 	/*
 	 * Okay, now we can let init(8) exec!  It's off to userland!
 	 */