On Tue, Jan 02, 2024 at 10:16:04AM +0530, Aneesh Kumar K.V wrote:
> Michael Ellerman <m...@ellerman.id.au> writes:
>
> ....
>
> > #ifdef CONFIG_PPC64
> > int boot_cpu_hwid = -1;
> > @@ -492,12 +493,26 @@ void __init smp_setup_cpu_maps(void)
> > avail = !of_property_match_string(dn,
> > "enable-method", "spin-table");
> >
> > - cpu = assign_threads(cpu, nthreads, avail, intserv);
> > + if (boot_core_hwid >= 0) {
> > + if (cpu == 0) {
> > + pr_info("Skipping CPU node %pOF to allow for
> > boot core.\n", dn);
> > + cpu = nthreads;
> > + continue;
> > + }
> >
> > - if (cpu >= nr_cpu_ids) {
> > + if (be32_to_cpu(intserv[0]) == boot_core_hwid) {
> > + pr_info("Renumbered boot core %pOF to logical
> > 0\n", dn);
> > + assign_threads(0, nthreads, avail, intserv);
> > + of_node_put(dn);
> > + break;
> >
>
> I was expecting a 'continue' here. Why 'break' the loop? The condition that
> should break the loop should be cpu >= nr_cpu_ids
No, the patch seems correct:
We're in the "if (boot_core_hwid >= 0)" branch, meaning that it
was determined by early_init_dt_scan_cpus() that boot_cpuid >=
nr_cpu_ids. So we loop until we get to the boot CPU, so it can be
renumbered to 0. Once we do that we break, because we
know we are already past nr_cpu_ids - otherwise boot_core_hwid
would not be >= 0.
> > + }
> > + } else if (cpu >= nr_cpu_ids) {
> > of_node_put(dn);
> > break;
> > }
Here is what you expected - in case the boot CPU was < nr_cpu_ids
we break as soon as nr_cpu_ids is reached.
> > +
> > + if (cpu < nr_cpu_ids)
this ensures that CPUs between nr_cpu_ids and the boot CPU are
correctly ignored in case we're already past nr_cpu_ids and only
scanning further to find the boot CPU to be renumbered to 0
--
Jiri Bohac <jbo...@suse.cz>
SUSE Labs, Prague, Czechia
