Re: [PATCH v5 2/3] sched/topology: Rework CPU capacity asymmetry detection

Peter Zijlstra
2021-05-27T07:03:57Z

On Wed, May 26, 2021 at 11:52:25AM +0200, Dietmar Eggemann wrote:

> For me asym_cpu_capacity_classify() is pretty hard to digest ;-) But I
> wasn't able to break it. It also performs correctly on (non-existing SMT)
> layer (with sd span eq. single CPU).

This is the simplest form I could come up with this morning:

static inline int
asym_cpu_capacity_classify(struct sched_domain *sd,
const struct cpumask *cpu_map)
{
struct asym_cap_data *entry;
int i = 0, n = 0;

list_for_each_entry(entry, &asym_cap_list, link) {
if (cpumask_intersects(sched_domain_span(sd), entry->cpu_mask))
i++;
else
n++;
}

if (WARN_ON_ONCE(!i) || i == 1) /* no asymmetry */
return 0;

if (n) /* partial asymmetry */
return SD_ASYM_CPUCAPACITY;

/* full asymmetry */
return SD_ASYM_CPUCAPACITY | SD_ASYM_CPUCAPACITY_FULL;
}

The early termination and everything was cute; but this isn't
performance critical code and clarity is paramount.