[PATCH 08/11] arm64: pmu: Provide cpumask attribute for PMU

[jeremy.linton@arm.com (Jeremy Linton)]

Hi,

On 07/07/2016 11:21 AM, Mark Rutland wrote:
> Hi Jeremy,
>
> Apologies for the late reply on this.
>
> On Tue, Jun 21, 2016 at 12:11:46PM -0500, Jeremy Linton wrote:
>> With heterogeneous PMUs its helpful to know which PMUs are bound
>> to each CPU. Provide that information with a cpumask sysfs entry
>> similar to other PMUs.
>
> Have you tested trying to stat on a particular PMU? e.g.
>
> $ perf stat -e armv8_cortex_a53/cpu_cycles/ ls
>
> I found that the presence of a cpumask file would cause (at least some
> versions) of perf-stat to hang, and was holding off adding a cpumask
> until we had a solution to that.

Nice!

I guess that is more proof that any tiny change can break things.. 
Another "fix" is to make the cpumap_print_to_pagebuf's first parameter 
false which apparently keeps perf from understanding the cpu mask and 
forces the user to use numactl, which is ugly because numactrl doesn't 
understand the mask in that format either.

I guess fixing perf is probably the best bet here...



>
> See [1,2] for more details on that.
>
>> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
>> ---
>>   arch/arm64/kernel/perf_event.c | 21 +++++++++++++++++++++
>>   1 file changed, 21 insertions(+)
>
> This should be generic across the arm-pmu code, and so should live under
> drivers/perf/.

Which is where i had it initially, but (IIRC) getting to work there 
required some core pmu changes that seemed a little ugly. I guess I 
didn't like the idea of reallocating the per pmu attr group or tweaking 
the pmu core code.. So I just moved it into perf_event where it fit more 
naturally.



>
> Thanks,
> Mark.
>
> [1] http://lkml.kernel.org/r/1467907474-3290-1-git-send-email-mark.rutland at arm.com
> [2] http://lkml.kernel.org/r/1467907474-3290-2-git-send-email-mark.rutland at arm.com
>
>> diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
>> index 356fa6c..dae73ea 100644
>> --- a/arch/arm64/kernel/perf_event.c
>> +++ b/arch/arm64/kernel/perf_event.c
>> @@ -533,6 +533,26 @@ static struct attribute_group armv8_pmuv3_events_attr_group = {
>>
>>   PMU_FORMAT_ATTR(event, "config:0-9");
>>
>> +static ssize_t
>> +cpumask_show(struct device *dev, struct device_attribute *attr, char *page)
>> +{
>> +	struct pmu *pmu = dev_get_drvdata(dev);
>> +	struct arm_pmu *cpu_pmu = container_of(pmu, struct arm_pmu, pmu);
>> +
>> +	return cpumap_print_to_pagebuf(true, page, &cpu_pmu->supported_cpus);
>> +}
>> +static DEVICE_ATTR_RO(cpumask);
>> +
>> +static struct attribute *armv8_pmuv3_attrs[] = {
>> +	 &dev_attr_cpumask.attr,
>> +	 NULL,
>> +};
>> +
>> +static struct attribute_group armv8_pmuv3_attr_group = {
>> +	.attrs = armv8_pmuv3_attrs,
>> +};
>> +
>> +
>>   static struct attribute *armv8_pmuv3_format_attrs[] = {
>>   	&format_attr_event.attr,
>>   	NULL,
>> @@ -544,6 +564,7 @@ static struct attribute_group armv8_pmuv3_format_attr_group = {
>>   };
>>
>>   static const struct attribute_group *armv8_pmuv3_attr_groups[] = {
>> +	&armv8_pmuv3_attr_group,
>>   	&armv8_pmuv3_events_attr_group,
>>   	&armv8_pmuv3_format_attr_group,
>>   	NULL,
>> --
>> 2.5.5
>>
>