Re: [PATCH v2 06/23] sched/cache: Track LLC-preferred tasks per runqueue

[Chen, Yu C]

On 12/10/2025 5:42 PM, Peter Zijlstra wrote:
> On Tue, Dec 09, 2025 at 02:55:21PM -0800, Tim Chen wrote:
>
> > > > +static void account_llc_dequeue(struct rq *rq, struct task_struct *p)
> > > > +{
> > > > +	int pref_llc;
> > > > +
> > > > +	/*
> > > > +	 * Borrow the uc_se->active from uclamp_rq_inc_id(),
> > > > +	 * uclamp_rq_dec_id() to avoid the unbalanced calculation
> > > > +	 * of rq statistics.
> > > > +	 */
> > > > +	if (unlikely(!p->sched_llc_active))
> > > > +		return;
> > >
> > > Another very confusing comment; what? Also, can you please explain (in
> > > the new comment) how we get here without having llc_active set?
> >
> > The comment meant to say that we are using a similar mechanism as
> > accounting done in uc_se->active from uclamp_rq_inc_id(). I agree that
> > it confuses more than making things clearer.
> >
> > How about the following comment to make things clearer:
> >
> > 	/*
> > 	 * Cache aware scheduling was active when the task was enqueued.
> > 	 * Admin has disabled cache aware scheduling before task was dequeued
> > 	 * but the accounting has to be kept straight in case cache aware scheduling
> > 	 * is re-enabled.
> > 	 */
>
> Is having that sched_cache_enabled() test worth it?
> account_numa_{en,de}queue() don't seem to have any of this.

OK, I think we can remove the sched_cache_enabled() check and
make the account_llc_{en,de}queue() depending on CONFIG_SCHED_CACHE,
so the sched_llc_active can be removed.

thanks,
Chenyu