linux-kernel - Re: [PATCH v3 3/8] sched/topology: Switch to assigning "sd->shared" from s

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Message-ID: <xhsmh7bsr3zel.mognet@vschneid-thinkpadt14sgen2i.remote.csb>
Date: Thu, 05 Feb 2026 17:53:22 +0100
From: Valentin Schneider <vschneid@...hat.com>
To: K Prateek Nayak <kprateek.nayak@....com>, Ingo Molnar
 <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Juri Lelli
 <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>,
 linux-kernel@...r.kernel.org
Cc: Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt
 <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel Gorman
 <mgorman@...e.de>, Chen Yu <yu.c.chen@...el.com>, Shrikanth Hegde
 <sshegde@...ux.ibm.com>, "Gautham R.
 Shenoy" <gautham.shenoy@....com>, K Prateek Nayak <kprateek.nayak@....com>
Subject: Re: [PATCH v3 3/8] sched/topology: Switch to assigning "sd->shared"
 from s_data

On 20/01/26 11:32, K Prateek Nayak wrote:
> @@ -2655,8 +2655,19 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
>               unsigned int imb_span = 1;
>
>               for (sd = *per_cpu_ptr(d.sd, i); sd; sd = sd->parent) {
> +			struct sched_domain *parent = sd->parent;
>                       struct sched_domain *child = sd->child;
>
> +			/* Attach sd->shared to the topmost SD_SHARE_LLC domain. */
> +			if ((sd->flags & SD_SHARE_LLC) &&
> +			    (!parent || !(parent->flags & SD_SHARE_LLC))) {
> +				int llc_id = cpumask_first(sched_domain_span(sd));
> +
> +				sd->shared = *per_cpu_ptr(d.sds, llc_id);
> +				atomic_set(&sd->shared->nr_busy_cpus, sd->span_weight);
> +				atomic_inc(&sd->shared->ref);
> +			}
> +

We now have two if's looking for the highest_flag_domain(i, SD_SHARE_LLC),
but given this needs to write the sd->imb_numa_nr for every SD I couldn't
factorize this into something that looked sane :(

>                       if (!(sd->flags & SD_SHARE_LLC) && child &&
>                           (child->flags & SD_SHARE_LLC)) {
>                               struct sched_domain __rcu *top_p;