Messages in this thread | | | Date | Tue, 16 Jun 2015 11:58:09 +0530 | From | Preeti U Murthy <> | Subject | Re: [PATCH v2 7/7]powerpc/powernv: nest pmu cpumask and cpu hotplug support |
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On 06/11/2015 10:47 AM, Madhavan Srinivasan wrote: > Adds cpumask attribute to be used by each nest pmu since nest > units are per-chip. Only one cpu (first online cpu) from each node/chip > is designated to read counters. > > On cpu hotplug, dying cpu is checked to see whether it is one of the > designated cpus, if yes, next online cpu from the same node/chip is designated > as new cpu to read counters. > > Cc: Michael Ellerman <mpe@ellerman.id.au> > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> > Cc: Paul Mackerras <paulus@samba.org> > Cc: Anton Blanchard <anton@samba.org> > Cc: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com> > Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com> > Cc: Stephane Eranian <eranian@google.com> > Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com> > Cc: Ingo Molnar <mingo@kernel.org> > Cc: Peter Zijlstra <peterz@infradead.org> > Signed-off-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com> > --- > +static void nest_change_cpu_context(int old_cpu, int new_cpu) > +{ > + int i; > + > + if (new_cpu >= 0) { > + for (i = 0; per_nest_pmu_arr[i] != NULL; i++) > + perf_pmu_migrate_context(&per_nest_pmu_arr[i]->pmu, > + old_cpu, new_cpu); > + } > +} > + > +static void nest_exit_cpu(int cpu) > +{ > + int i, nid, target = -1; > + const struct cpumask *l_cpumask; > + int src_chipid; > + > + /* > + * Check in the designated list for this cpu. Dont bother > + * if not one of them. > + */ > + if (!cpumask_test_and_clear_cpu(cpu, &cpu_mask_nest_pmu)) > + return; > + > + /* > + * Now that this cpu is one of the designated, > + * find a new cpu a) which is not dying and
This comment is not right. nest_exit_cpu() is called in the hotplug path, so another cpu cannot be dying in parallel. Hotplug operations are done serially. The comment ought to be "a) which is online" instead.
> + * b) is in same node/chip.
node is not the same as a chip right ? And you are interested in cpus on the same chip alone. So shouldn't the above comment be b) in the same chip ?
> + */ > + nid = cpu_to_node(cpu); > + src_chipid = topology_physical_package_id(cpu);
What is the relation between a node and a chip ? Can't we have a function which returns the cpumask of a chip straight away, since that is what you seem to be more interested in ? You can then simply choose the next cpu in this cpumask rather than going through the below loop.
> + l_cpumask = cpumask_of_node(nid); > + for_each_cpu(i, l_cpumask) { > + if (i == cpu) > + continue; > + if (src_chipid == topology_physical_package_id(i)) { > + target = i; > + break; > + } > + } > + > + /* > + * Update the cpumask with the target cpu and > + * migrate the context if needed > + */ > + if (target >= 0) {
You already check for target >= 0 here. So you don't need to check for new_cpu >= 0 in nest_change_cpu_context() above ?
> + cpumask_set_cpu(target, &cpu_mask_nest_pmu); > + nest_change_cpu_context (cpu, target); > + } > +} > + > +static void nest_init_cpu(int cpu) > +{ > + int i, src_chipid; > + > + /* > + * Search for any existing designated thread from > + * the incoming cpu's node/chip. If found, do nothing. > + */ > + src_chipid = topology_physical_package_id(cpu); > + for_each_cpu(i, &cpu_mask_nest_pmu) > + if (src_chipid == topology_physical_package_id(i)) > + return; > + > + /* > + * Make incoming cpu as a designated thread for > + * this node/chip > + */ > + cpumask_set_cpu(cpu, &cpu_mask_nest_pmu);
Why can't we simply check if cpu is the first one coming online in the chip and designate it as the cpu_mask_nest_pmu for that chip ? If it is not the first cpu, it means that another cpu in the same chip already took over this duty and it needn't bother.
And shouldn't we also call nest_init() on this cpu, just like you do in cpumask_chip() on all cpu_mask_nest_pmu cpus ?
> +} > + > +static int nest_cpu_notifier(struct notifier_block *self, > + unsigned long action, void *hcpu) > +{ > + long cpu = (long)hcpu; > + > + switch (action & ~CPU_TASKS_FROZEN) { > + case CPU_DOWN_FAILED:
Why do we need to handle the DOWN_FAILED case ? In DOWN_PREPARE, you have ensured that the function moves on to another cpu. So even if the offline failed, its no issue. The duty is safely taken over.
> + case CPU_STARTING:
I would suggest initializing nest in the CPU_ONLINE stage. This is because CPU_STARTING phase can fail. In that case, we will be unnecessarily initializing nest pre-maturely. CPU_ONLINE phase assures that the cpu is successfully online and you can then initiate nest.
> + nest_init_cpu(cpu); > + break; > + case CPU_DOWN_PREPARE: > + nest_exit_cpu(cpu); > + break; > + default: > + break; > + } > + > + return NOTIFY_OK; > +} > + > +static struct notifier_block nest_cpu_nb = { > + .notifier_call = nest_cpu_notifier, > + .priority = CPU_PRI_PERF + 1, > +}; > + > +void cpumask_chip(void)
This name ^^ is not apt IMO. You are initiating the cpumask necessary for nest pmu. So why not call it nest_pmu_cpumask_init() ?
> +{ > + const struct cpumask *l_cpumask; > + int cpu, nid; > + > + if (!cpumask_empty(&cpu_mask_nest_pmu))
When can this condition become true ?
> + return; > + > + cpu_notifier_register_begin(); > + > + /* > + * Nest PMUs are per-chip counters. So designate a cpu > + * from each node/chip for counter collection. > + */ > + for_each_online_node(nid) { > + l_cpumask = cpumask_of_node(nid); > + > + /* designate first online cpu in this node */ > + cpu = cpumask_first(l_cpumask); > + cpumask_set_cpu(cpu, &cpu_mask_nest_pmu); > + } > + > + /* Initialize Nest PMUs in each node using designated cpus */ > + on_each_cpu_mask(&cpu_mask_nest_pmu, (smp_call_func_t)nest_init, NULL, 1); > + > + __register_cpu_notifier(&nest_cpu_nb); > + > + cpu_notifier_register_done(); > +}
Regards Preeti U Murthy
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