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

[Chen, Yu C]

On 2/19/2026 7:21 AM, Tim Chen wrote:
> On Wed, 2026-02-18 at 23:16 +0530, K Prateek Nayak wrote:
> > Hello Chenyu,
> >
> > On 2/18/2026 8:52 PM, Chen, Yu C wrote:

[ ... ]

> Pratek,
>
> How about modifying the patch like the following, stealing
> a lot of your code.  Also added change to shrink max LLCs when
> the LLC with max id lost its last CPU.
>
> Thanks.

[ ... ]

> +
> +static void __sched_domains_free_llc_id(int cpu)
> +{
> +	int i, lid;
> +
> +	lockdep_assert_held(&sched_domains_mutex);
> +
> +	lid = per_cpu(sd_llc_id, cpu);
> +	if (lid == -1)
> +		return;
> +
> +	per_cpu(sd_llc_id, cpu) = -1;
> +
> +	for_each_online_cpu(i) {

One minor question: should we only iterate through
cpu_coregroup_mask(cpu) to check if any sibling CPU
within this LLC owns the llc_id? If there are no online
CPUs within this LLC, I assume we should release this
llc_id.

thanks,
Chenyu

> +		/* 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);