Re: [PATCH v3 09/21] sched/cache: Count tasks prefering destination LLC in a sched group

[Peter Zijlstra]

On Fri, Feb 20, 2026 at 01:52:48PM +0100, Peter Zijlstra wrote:
> On Tue, Feb 10, 2026 at 02:18:49PM -0800, Tim Chen wrote:
> 
> > @@ -11034,6 +11037,9 @@ static inline void update_sg_lb_stats(struct lb_env *env,
> >  {
> >  	int i, nr_running, local_group, sd_flags = env->sd->flags;
> >  	bool balancing_at_rd = !env->sd->parent;
> > +#ifdef CONFIG_SCHED_CACHE
> > +	int dst_llc = llc_id(env->dst_cpu);
> > +#endif
> >  
> >  	memset(sgs, 0, sizeof(*sgs));
> >  
> > @@ -11054,6 +11060,15 @@ static inline void update_sg_lb_stats(struct lb_env *env,
> >  		if (cpu_overutilized(i))
> >  			*sg_overutilized = 1;
> >  
> > +#ifdef CONFIG_SCHED_CACHE
> > +		if (sched_cache_enabled() && llc_id(i) != dst_llc) {
> 
> If you write that like:
> 
> 		if (sched_cache_enabled && llc_id(i) != llc_id(env->dst_cpu))
> 
> You can get rid of that dst_llc variable, but more importantly its
> ifdeffery.

Ah, you're perhaps wanting to not re-load on the dst_llc usage below? Do
the compilers DTRT when you mark llc_id() as __pure?

> > +			struct sched_domain *sd_tmp = rcu_dereference(rq->sd);
> > +
> > +			if (valid_llc_buf(sd_tmp, dst_llc))
> > +				sgs->nr_pref_dst_llc += sd_tmp->pf[dst_llc];
> > +		}
> > +#endif
> 
>