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

Ian Rogers
2022-05-19T21:37:20Z

On Thu, May 19, 2022 at 4:29 AM Athira Rajeev
<atrajeev@linux.vnet.ibm.com> wrote:
>
> > 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, I've no problem with the change. Do we need to do a similar
discovery in the perf tool on old kernels? Perhaps then this
information could be exposed in the perf list command for self tests.

Thanks,
Ian

> 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
>