* Gautham R Shenoy <e...@linux.vnet.ibm.com> [2021-04-15 22:41:34]:
> Hi Srikar,
>
>
Thanks for taking a look.
> > @@ -1485,12 +1486,36 @@ static void add_cpu_to_masks(int cpu)
> > add_cpu_to_smallcore_masks(cpu);
> >
> > /* In CPU-hotplug path, hence use GFP_ATOMIC */
> > - alloc_cpumask_var_node(&mask, GFP_ATOMIC, cpu_to_node(cpu));
> > + ret = alloc_cpumask_var_node(&mask, GFP_ATOMIC, cpu_to_node(cpu));
> > update_mask_by_l2(cpu, &mask);
> >
> > if (has_coregroup_support())
> > update_coregroup_mask(cpu, &mask);
> >
> > + if (chip_id == -1 || !ret) {
> > + cpumask_copy(per_cpu(cpu_core_map, cpu), cpu_cpu_mask(cpu));
> > + goto out;
> > + }
> > +
> > + if (shared_caches)
> > + submask_fn = cpu_l2_cache_mask;
> > +
> > + /* Update core_mask with all the CPUs that are part of submask */
> > + or_cpumasks_related(cpu, cpu, submask_fn, cpu_core_mask);
> >
>
> If coregroups exist, we can add the cpus of the coregroup to the
> cpu_core_mask thereby reducing the scope of the for_each_cpu() search
> below. This will still cut down the time on Baremetal systems
> supporting coregroups.
>
Yes, once we upstream coregroup support to Baremetal, we should look
at adding it. Also do note, number of CPUs we support for Baremetal is
comparatively lower than in PowerVM + QEMU. And more importantly the
number of cores per coregroup is also very low. So the optimization
may not yield too much of a benefit.
Its only in the QEMU case, where we end up having too many cores in
the same chip, where we see a drastic increase in the boot-up time.
--
Thanks and Regards
Srikar Dronamraju
