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SubjectRe: [PATCH v3 2/2] perf/arm-ccn: Clean up CPU hotplug handling
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On 16/04/2019 17:29, Suzuki K Poulose wrote:
> On 04/16/2019 04:24 PM, Robin Murphy wrote:
>> Like arm-cci, arm-ccn has the same issue of disabling preemption around
>> operations which can take mutexes. Again, remove the definite bug by
>> simply not trying to fight the theoretical races. And since we are
>> touching the hotplug handling code, take the opportunity to streamline
>> it, as there's really no need to store a full-sized cpumask to keep
>> track of a single CPU ID.
>>
>> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
>> ---
>>   drivers/perf/arm-ccn.c | 25 +++++++++++++------------
>>   1 file changed, 13 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/perf/arm-ccn.c b/drivers/perf/arm-ccn.c
>> index 2ae76026e947..0bb52d9bdcf7 100644
>> --- a/drivers/perf/arm-ccn.c
>> +++ b/drivers/perf/arm-ccn.c
>> @@ -167,7 +167,7 @@ struct arm_ccn_dt {
>>       struct hrtimer hrtimer;
>> -    cpumask_t cpu;
>> +    unsigned int cpu;
>>       struct hlist_node node;
>>       struct pmu pmu;
>> @@ -559,7 +559,7 @@ static ssize_t arm_ccn_pmu_cpumask_show(struct
>> device *dev,
>>   {
>>       struct arm_ccn *ccn = pmu_to_arm_ccn(dev_get_drvdata(dev));
>> -    return cpumap_print_to_pagebuf(true, buf, &ccn->dt.cpu);
>> +    return cpumap_print_to_pagebuf(true, buf, cpumask_of(ccn->dt.cpu));
>>   }
>>   static struct device_attribute arm_ccn_pmu_cpumask_attr =
>> @@ -759,7 +759,7 @@ static int arm_ccn_pmu_event_init(struct
>> perf_event *event)
>>        * mitigate this, we enforce CPU assignment to one, selected
>>        * processor (the one described in the "cpumask" attribute).
>>        */
>> -    event->cpu = cpumask_first(&ccn->dt.cpu);
>> +    event->cpu = ccn->dt.cpu;
>>       node_xp = CCN_CONFIG_NODE(event->attr.config);
>>       type = CCN_CONFIG_TYPE(event->attr.config);
>> @@ -1215,15 +1215,15 @@ static int arm_ccn_pmu_offline_cpu(unsigned
>> int cpu, struct hlist_node *node)
>>       struct arm_ccn *ccn = container_of(dt, struct arm_ccn, dt);
>>       unsigned int target;
>> -    if (!cpumask_test_and_clear_cpu(cpu, &dt->cpu))
>> +    if (cpu != dt->cpu)
>>           return 0;
>>       target = cpumask_any_but(cpu_online_mask, cpu);
>>       if (target >= nr_cpu_ids)
>>           return 0;
>>       perf_pmu_migrate_context(&dt->pmu, cpu, target);
>> -    cpumask_set_cpu(target, &dt->cpu);
>> +    dt->cpu = target;
>>       if (ccn->irq)
>> -        WARN_ON(irq_set_affinity_hint(ccn->irq, &dt->cpu) != 0);
>> +        WARN_ON(irq_set_affinity_hint(ccn->irq, cpumask_of(dt->cpu)));
>>       return 0;
>>   }
>> @@ -1299,29 +1299,30 @@ static int arm_ccn_pmu_init(struct arm_ccn *ccn)
>>       }
>>       /* Pick one CPU which we will use to collect data from CCN... */
>> -    cpumask_set_cpu(get_cpu(), &ccn->dt.cpu);
>> +    ccn->dt.cpu = raw_smp_processor_id();
>>       /* Also make sure that the overflow interrupt is handled by this
>> CPU */
>>       if (ccn->irq) {
>> -        err = irq_set_affinity_hint(ccn->irq, &ccn->dt.cpu);
>> +        err = irq_set_affinity_hint(ccn->irq, cpumask_of(ccn->dt.cpu));
>>           if (err) {
>>               dev_err(ccn->dev, "Failed to set interrupt affinity!\n");
>>               goto error_set_affinity;
>>           }
>>       }
>> +    cpuhp_state_add_instance_nocalls(CPUHP_AP_PERF_ARM_CCN_ONLINE,
>> +                     &ccn->dt.node);
>> +
>>       err = perf_pmu_register(&ccn->dt.pmu, name, -1);
>>       if (err)
>>           goto error_pmu_register;
>> -    cpuhp_state_add_instance_nocalls(CPUHP_AP_PERF_ARM_CCN_ONLINE,
>> -                     &ccn->dt.node);
>> -    put_cpu();
>>       return 0;
>>   error_pmu_register:
>> +    cpuhp_state_remove_instance_nocalls(CPUHP_AP_PERF_ARM_CCN_ONLINE,
>> +                        &ccn->dt.node);
>>   error_set_affinity:
>> -    put_cpu();
>
> Super minor nit: We don't need the error_set_affinity label anymore, as
> we don't do anything here. Otherwise:

Right, there were already somewhat-redundant labels to begin with, but
since they remain consistently named for the failure conditions which
lead to them (as opposed to the cleanup action that they take) I figured
I would leave them be for this change.

> Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>

Thanks!

Robin.

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