Re: [PATCH v7 08/14] sched/topology: Disable EAS on inappropriate platforms

[Quentin Perret <quentin.perret@arm.com>]

On Wednesday 03 Oct 2018 at 18:27:19 (+0200), Peter Zijlstra wrote:
> On Wed, Sep 12, 2018 at 10:13:03AM +0100, Quentin Perret wrote:
> > @@ -288,6 +321,21 @@ static void build_perf_domains(const struct cpumask *cpu_map)
> >  			goto free;
> >  		tmp->next = pd;
> >  		pd = tmp;
> > +
> > +		/*
> > +		 * Count performance domains and capacity states for the
> > +		 * complexity check.
> > +		 */
> > +		nr_pd++;
> > +		nr_cs += em_pd_nr_cap_states(pd->obj);
> > +	}
> > +
> > +	/* Bail out if the Energy Model complexity is too high. */
> > +	if (nr_pd * (nr_cs + nr_cpus) > EM_MAX_COMPLEXITY) {
> > +		if (sched_debug())
> > +			pr_info("rd %*pbl: EM complexity is too high\n ",
> > +						cpumask_pr_args(cpu_map));
> > +		goto free;
> >  	}
> 
> I would make than an unconditional WARN, we do not really expect that to
> trigger, but then it does, we really don't want to hide it.

OTOH that also means that some people with big asymmetric machines can
get a WARN message every time they boot, and even if they don't want to
use EAS.

Now, that shouldn't happen any time soon, so it's maybe a good thing if
we get reports when/if people start to hit that one, so why not ...

Thanks,
Quentin