On Mon, 15 May 2017, Madhavan Srinivasan wrote:
> On Wednesday 10 May 2017 05:39 PM, Thomas Gleixner wrote:
> > On Thu, 4 May 2017, Anju T Sudhakar wrote:
> > > + /*
> > > + * Update the cpumask with the target cpu and
> > > + * migrate the context if needed
> > > + */
> > > + if (target >= 0 && target <= nr_cpu_ids) {
> > > + cpumask_set_cpu(target, &nest_imc_cpumask);
> > > + nest_change_cpu_context(cpu, target);
> > > + }
> > What disables the perf context if this was the last CPU on the node?
>
> My bad. i did not understand this. Is this regarding the updates
> of the "flags" in the perf_event and hw_perf_event structs?
Sorry, there is nothing to understand. It was me misreading it.
> > > +static int nest_pmu_cpumask_init(void)
> > > +{
> > > + const struct cpumask *l_cpumask;
> > > + int cpu, nid;
> > > + int *cpus_opal_rc;
> > > +
> > > + if (!cpumask_empty(&nest_imc_cpumask))
> > > + return 0;
> > What's that for? Paranoia engineering?
>
> No. The idea here is to generate the cpu_mask attribute
> field only for the first "nest" pmu and use the same
> for other "nest" units.
Why is nest_pmu_cpumask_init() called more than once? If it is then you
should have a proper flag marking it initialiazed rather than making a
completely obscure check for a cpu mask. That check could be empty for the
second invocation when the first invocation fails.
> > But this whole function is completely overengineered. If you make that
> > nest_init() part of the online function then this works also for nodes
> > which come online later and it simplifies to:
> >
> > static int ppc_nest_imc_cpu_online(unsigned int cpu)
> > {
> > const struct cpumask *l_cpumask;
> > static struct cpumask tmp_mask;
> > int res;
> >
> > /* Get the cpumask of this node */
> > l_cpumask = cpumask_of_node(cpu_to_node(cpu));
> >
> > /*
> > * If this is not the first online CPU on this node, then IMC is
> > * initialized already.
> > */
> > if (cpumask_and(&tmp_mask, l_cpumask, &nest_imc_cpumask))
> > return 0;
> >
> > /*
> > * If this fails, IMC is not usable.
> > *
> > * FIXME: Add a understandable comment what this actually does
> > * and why it can fail.
> > */
> > res = opal_imc_counters_stop(OPAL_IMC_COUNTERS_NEST);
> > if (res)
> > return res;
> >
> > /* Make this CPU the designated target for counter collection */
> > cpumask_set_cpu(cpu, &nest_imc_cpumask);
> > nest_change_cpu_context(-1, cpu);
> > return 0;
> > }
> >
> > static int nest_pmu_cpumask_init(void)
> > {
> > return cpuhp_setup_state(CPUHP_AP_PERF_POWERPC_NEST_ONLINE,
> > "perf/powerpc/imc:online",
> > ppc_nest_imc_cpu_online,
> > ppc_nest_imc_cpu_offline);
> > }
> >
> > Hmm?
>
> Yes this make sense. But we need to first designate a cpu in each
> chip at init setup and use opal api to disable the engine in the same.
> So probably, after cpuhp_setup_state, can we do that?
Errm. That's what ppc_nest_imc_cpu_online() does.
It checks whether this is the first online cpu on a node and if yes, it
calls opal_imc_counters_stop() and sets that cpu in nest_imc_cpumask.
cpuhp_setup_state() invokes the callback on each online CPU. Seo evrything
is set up proper after that.
Thanks,
tglx
