Re: [PATCH V2 1/2] powerpc/perf: Add support for caps under sysfs in powerpc

Athira Rajeev
2022-05-19T11:29:27Z

> On 19-May-2022, at 10:12 AM, Ian Rogers <irogers@google.com> wrote:
>
> On Wed, May 18, 2022 at 1:55 AM Athira Rajeev
> <atrajeev@linux.vnet.ibm.com> wrote:
>>
>> Add caps support under "/sys/bus/event_source/devices/<pmu>/"
>> for powerpc. This directory can be used to expose some of the
>> specific features that powerpc PMU supports to the user.
>> Example: pmu_name. The name of PMU registered will depend on
>> platform, say power9 or power10 or it could be Generic Compat
>> PMU.
>>
>> Currently the only way to know which is the registered
>> PMU is from the dmesg logs. But clearing the dmesg will make it
>> difficult to know exact PMU backend used. And even extracting
>> from dmesg will be complicated, as we need to parse the dmesg
>> logs and add filters for pmu name. Whereas by exposing it via
>> caps will make it easy as we just need to directly read it from
>> the sysfs.
>
> For ARM and x86 in the perf tool this is normally done through a cpuid
> like function, is there a reason to differ on Power?
>
> Thanks,
> Ian

Hi Ian,

Thanks for review. The information from cpuid or cpuinfo will provide
us the information of the platform/model/machine etc. In case of powerpc,
we have one case where, though platform points to specific generation of the
processor, say power9 or power10, the registered PMU could point to
different one. To be specific, this is named as Generic Compat PMU which
is a fallback PMU. This gets registered when the distro doesn't have support
for platform specific PMU. In that case distro will have a Generic
Compat PMU registered which supports basic features for performance monitoring.
This information can't be fetched from the cpuid data since that will point
to current platform.

So the pmu_name exposed via "caps" will be useful to detect the PMU
registered and also we target to use this information in some of our
selftests.

Thanks
Athira
>
>> Add a caps directory to /sys/bus/event_source/devices/cpu/
>> for power8, power9, power10 and generic compat PMU in respective
>> PMU driver code. Update the pmu_name file under caps folder
>> in core-book3s using "attr_update".
>>
>> The information exposed currently:
>> - pmu_name : Underlying PMU name from the driver
>>
>> Example result with power9 pmu:
>>
>> # ls /sys/bus/event_source/devices/cpu/caps
>> pmu_name
>>
>> # cat /sys/bus/event_source/devices/cpu/caps/pmu_name
>> POWER9
>>
>> Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
>> ---
>> Changelog:
>> v1 -> v2:
>> Move the show function as generic in core-book3s
>> and update show function using sysfs_emit and ppmu->name
>> Added Documention for this ABI in patch 2.
>> Notes: The caps directory is implemented in PMU for other
>> architectures already. Reference commit for x86:
>> commit b00233b53065 ("perf/x86: Export some PMU attributes in caps/ directory")
>>
>> arch/powerpc/perf/core-book3s.c | 31 ++++++++++++++++++++++++++
>> arch/powerpc/perf/generic-compat-pmu.c | 10 +++++++++
>> arch/powerpc/perf/power10-pmu.c | 10 +++++++++
>> arch/powerpc/perf/power8-pmu.c | 10 +++++++++
>> arch/powerpc/perf/power9-pmu.c | 10 +++++++++
>> 5 files changed, 71 insertions(+)
>>
>> diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
>> index b5b42cf0a703..a208f502a80b 100644
>> --- a/arch/powerpc/perf/core-book3s.c
>> +++ b/arch/powerpc/perf/core-book3s.c
>> @@ -2488,6 +2488,33 @@ static int power_pmu_prepare_cpu(unsigned int cpu)
>> return 0;
>> }
>>
>> +static ssize_t pmu_name_show(struct device *cdev,
>> + struct device_attribute *attr,
>> + char *buf)
>> +{
>> + if (ppmu)
>> + return sysfs_emit(buf, "%s\n", ppmu->name);
>> +
>> + return 0;
>> +}
>> +
>> +static DEVICE_ATTR_RO(pmu_name);
>> +
>> +static struct attribute *pmu_caps_attrs[] = {
>> + &dev_attr_pmu_name.attr,
>> + NULL
>> +};
>> +
>> +static const struct attribute_group pmu_caps_group = {
>> + .name = "caps",
>> + .attrs = pmu_caps_attrs,
>> +};
>> +
>> +static const struct attribute_group *pmu_caps_groups[] = {
>> + &pmu_caps_group,
>> + NULL,
>> +};
>> +
>> int __init register_power_pmu(struct power_pmu *pmu)
>> {
>> if (ppmu)
>> @@ -2498,6 +2525,10 @@ int __init register_power_pmu(struct power_pmu *pmu)
>> pmu->name);
>>
>> power_pmu.attr_groups = ppmu->attr_groups;
>> +
>> + if (ppmu->flags & PPMU_ARCH_207S)
>> + power_pmu.attr_update = pmu_caps_groups;
>> +
>> power_pmu.capabilities |= (ppmu->capabilities & PERF_PMU_CAP_EXTENDED_REGS);
>>
>> #ifdef MSR_HV
>> diff --git a/arch/powerpc/perf/generic-compat-pmu.c b/arch/powerpc/perf/generic-compat-pmu.c
>> index f3db88aee4dd..817c69863038 100644
>> --- a/arch/powerpc/perf/generic-compat-pmu.c
>> +++ b/arch/powerpc/perf/generic-compat-pmu.c
>> @@ -151,9 +151,19 @@ static const struct attribute_group generic_compat_pmu_format_group = {
>> .attrs = generic_compat_pmu_format_attr,
>> };
>>
>> +static struct attribute *generic_compat_pmu_caps_attrs[] = {
>> + NULL
>> +};
>> +
>> +static struct attribute_group generic_compat_pmu_caps_group = {
>> + .name = "caps",
>> + .attrs = generic_compat_pmu_caps_attrs,
>> +};
>> +
>> static const struct attribute_group *generic_compat_pmu_attr_groups[] = {
>> &generic_compat_pmu_format_group,
>> &generic_compat_pmu_events_group,
>> + &generic_compat_pmu_caps_group,
>> NULL,
>> };
>>
>> diff --git a/arch/powerpc/perf/power10-pmu.c b/arch/powerpc/perf/power10-pmu.c
>> index c6d51e7093cf..d1adcd9f52e2 100644
>> --- a/arch/powerpc/perf/power10-pmu.c
>> +++ b/arch/powerpc/perf/power10-pmu.c
>> @@ -258,6 +258,15 @@ static const struct attribute_group power10_pmu_format_group = {
>> .attrs = power10_pmu_format_attr,
>> };
>>
>> +static struct attribute *power10_pmu_caps_attrs[] = {
>> + NULL
>> +};
>> +
>> +static struct attribute_group power10_pmu_caps_group = {
>> + .name = "caps",
>> + .attrs = power10_pmu_caps_attrs,
>> +};
>> +
>> static const struct attribute_group *power10_pmu_attr_groups_dd1[] = {
>> &power10_pmu_format_group,
>> &power10_pmu_events_group_dd1,
>> @@ -267,6 +276,7 @@ static const struct attribute_group *power10_pmu_attr_groups_dd1[] = {
>> static const struct attribute_group *power10_pmu_attr_groups[] = {
>> &power10_pmu_format_group,
>> &power10_pmu_events_group,
>> + &power10_pmu_caps_group,
>> NULL,
>> };
>>
>> diff --git a/arch/powerpc/perf/power8-pmu.c b/arch/powerpc/perf/power8-pmu.c
>> index e37b1e714d2b..2518f5375d4a 100644
>> --- a/arch/powerpc/perf/power8-pmu.c
>> +++ b/arch/powerpc/perf/power8-pmu.c
>> @@ -187,9 +187,19 @@ static const struct attribute_group power8_pmu_events_group = {
>> .attrs = power8_events_attr,
>> };
>>
>> +static struct attribute *power8_pmu_caps_attrs[] = {
>> + NULL
>> +};
>> +
>> +static struct attribute_group power8_pmu_caps_group = {
>> + .name = "caps",
>> + .attrs = power8_pmu_caps_attrs,
>> +};
>> +
>> static const struct attribute_group *power8_pmu_attr_groups[] = {
>> &isa207_pmu_format_group,
>> &power8_pmu_events_group,
>> + &power8_pmu_caps_group,
>> NULL,
>> };
>>
>> diff --git a/arch/powerpc/perf/power9-pmu.c b/arch/powerpc/perf/power9-pmu.c
>> index c393e837648e..5c654ce1a417 100644
>> --- a/arch/powerpc/perf/power9-pmu.c
>> +++ b/arch/powerpc/perf/power9-pmu.c
>> @@ -258,9 +258,19 @@ static const struct attribute_group power9_pmu_format_group = {
>> .attrs = power9_pmu_format_attr,
>> };
>>
>> +static struct attribute *power9_pmu_caps_attrs[] = {
>> + NULL
>> +};
>> +
>> +static struct attribute_group power9_pmu_caps_group = {
>> + .name = "caps",
>> + .attrs = power9_pmu_caps_attrs,
>> +};
>> +
>> static const struct attribute_group *power9_pmu_attr_groups[] = {
>> &power9_pmu_format_group,
>> &power9_pmu_events_group,
>> + &power9_pmu_caps_group,
>> NULL,
>> };
>>
>> --
>> 2.31.1