Re: [PATCH v3 04/21] sched/cache: Make LLC id continuous

[Tim Chen <tim.c.chen@linux.intel.com>]

On Fri, 2026-02-20 at 20:30 +0100, Peter Zijlstra wrote:
> On Fri, Feb 20, 2026 at 11:24:11AM -0800, Tim Chen wrote:
> 
> > +static int __sched_domains_alloc_llc_id(void)
> > +{
> > +	int lid, max_lid;
> > +
> > +	lockdep_assert_held(&sched_domains_mutex);
> > +
> > +	lid = cpumask_first_zero(sched_domains_llc_id_allocmask);
> > +	/*
> > +	 * llc_id space should never grow larger than the
> > +	 * possible number of CPUs in the system.
> > +	 */
> > +	BUG_ON(lid >= nr_cpu_ids);
> 
> 	__cpumask_set_cpu(lid, sched_domains_llc_is_allocmask);

Ah yes, fat fingers delete one line too many.

> 
> > +	max_lid = cpumask_last(sched_domains_llc_id_allocmask);
> > +	/* size is one more than max index */
> > +	tl_max_llcs = max(lid, max_lid) + 1;
> > +
> > +	return lid;
> > +}
> > +
> > +static void __sched_domains_free_llc_id(int cpu)
> > +{
> > +	int i, lid, last_lid;
> > +
> > +	lockdep_assert_held(&sched_domains_mutex);
> > +
> > +	lid = per_cpu(sd_llc_id, cpu);
> > +	if (lid == -1)
> > +		return;
> > +
> > +	BUG_ON(lid >= nr_cpu_ids);
> > +	per_cpu(sd_llc_id, cpu) = -1;
> > +
> > +	for_each_cpu(i, cpu_coregroup_mask(cpu)) {
> > +		/* An online CPU owns the llc_id. */
> > +		if (per_cpu(sd_llc_id, i) == lid)
> > +			return;
> > +	}
> > +
> 	__cpumask_clear_cpu(lid, sched_domains_llc_id_allocmask);
> > +
> > +	last_lid = cpumask_last(sched_domains_llc_id_allocmask);
> > +	/* shrink max LLC size to save memory */
> > +	if (last_lid < tl_max_llcs - 1)
> > +		tl_max_llcs = last_lid + 1;
> > +}
> 
> Might be simpler to just track max_lid, and do the +1 at the alloc site?
> 
Sure, will do.  Will also update the code to validate lid value accordingly.

Tim