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Subject: Re: [PATCH V2 1/2] powerpc/perf: Add support for caps under sysfs in
 powerpc
From:   Athira Rajeev <atrajeev@linux.vnet.ibm.com>
In-Reply-To: <CAP-5=fURkncicNEs87=QisBJhPkujRUZ51Z1S4A63fz+SXV6rg@mail.gmail.com>
Date:   Fri, 20 May 2022 11:44:52 +0530
Cc:     maddy@linux.vnet.ibm.com,
        Nageswara Sastry <rnsastry@linux.ibm.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        linux-perf-users@vger.kernel.org, Jiri Olsa <jolsa@kernel.org>,
        Kajol Jain <kjain@linux.ibm.com>, disgoel@linux.vnet.ibm.com,
        linuxppc-dev@lists.ozlabs.org
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References: <20220518085502.6914-1-atrajeev@linux.vnet.ibm.com>
 <CAP-5=fWN3Sgyp_hTyYvDrLrnr-7dj6ozERn0tDm5MrU2SEJ2Fg@mail.gmail.com>
 <4D9BD7B3-1FA0-4EFE-A7D9-75BBB84ED308@linux.vnet.ibm.com>
 <CAP-5=fURkncicNEs87=QisBJhPkujRUZ51Z1S4A63fz+SXV6rg@mail.gmail.com>
To:     Ian Rogers <irogers@google.com>
Precedence: bulk


> On 20-May-2022, at 3:06 AM, Ian Rogers <irogers@google.com> wrote:
>=20
> On Thu, May 19, 2022 at 4:29 AM Athira Rajeev
> <atrajeev@linux.vnet.ibm.com> wrote:
>>=20
>>> On 19-May-2022, at 10:12 AM, Ian Rogers <irogers@google.com> wrote:
>>>=20
>>> On Wed, May 18, 2022 at 1:55 AM Athira Rajeev
>>> <atrajeev@linux.vnet.ibm.com> wrote:
>>>>=20
>>>> 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.
>>>>=20
>>>> 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.
>>>=20
>>> 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?
>>>=20
>>> Thanks,
>>> Ian
>>=20
>> Hi Ian,
>>=20
>> 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.
>>=20
>> 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.
>=20
> 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.


Hi Ian,

Thanks for review. Thats good one to have. I see in perf tools, we are =
parsing caps data : "env->cpu_pmu_caps" already.
I will check on how this is used and option of having in perf list.
After checking, I will send a follow up patch for the same.

Thanks
Athira
>=20
> Thanks,
> Ian
>=20
>> Thanks
>> Athira
>>>=20
>>>> 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".
>>>>=20
>>>> The information exposed currently:
>>>> - pmu_name : Underlying PMU name from the driver
>>>>=20
>>>> Example result with power9 pmu:
>>>>=20
>>>> # ls /sys/bus/event_source/devices/cpu/caps
>>>> pmu_name
>>>>=20
>>>> # cat /sys/bus/event_source/devices/cpu/caps/pmu_name
>>>> POWER9
>>>>=20
>>>> 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")
>>>>=20
>>>> 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(+)
>>>>=20
>>>> 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;
>>>> }
>>>>=20
>>>> +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[] =3D {
>>>> +       &dev_attr_pmu_name.attr,
>>>> +       NULL
>>>> +};
>>>> +
>>>> +static const struct attribute_group pmu_caps_group =3D {
>>>> +       .name  =3D "caps",
>>>> +       .attrs =3D pmu_caps_attrs,
>>>> +};
>>>> +
>>>> +static const struct attribute_group *pmu_caps_groups[] =3D {
>>>> +       &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);
>>>>=20
>>>>      power_pmu.attr_groups =3D ppmu->attr_groups;
>>>> +
>>>> +       if (ppmu->flags & PPMU_ARCH_207S)
>>>> +               power_pmu.attr_update =3D pmu_caps_groups;
>>>> +
>>>>      power_pmu.capabilities |=3D (ppmu->capabilities & =
PERF_PMU_CAP_EXTENDED_REGS);
>>>>=20
>>>> #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 =3D {
>>>>      .attrs =3D generic_compat_pmu_format_attr,
>>>> };
>>>>=20
>>>> +static struct attribute *generic_compat_pmu_caps_attrs[] =3D {
>>>> +       NULL
>>>> +};
>>>> +
>>>> +static struct attribute_group generic_compat_pmu_caps_group =3D {
>>>> +       .name  =3D "caps",
>>>> +       .attrs =3D generic_compat_pmu_caps_attrs,
>>>> +};
>>>> +
>>>> static const struct attribute_group =
*generic_compat_pmu_attr_groups[] =3D {
>>>>      &generic_compat_pmu_format_group,
>>>>      &generic_compat_pmu_events_group,
>>>> +       &generic_compat_pmu_caps_group,
>>>>      NULL,
>>>> };
>>>>=20
>>>> 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 =3D {
>>>>      .attrs =3D power10_pmu_format_attr,
>>>> };
>>>>=20
>>>> +static struct attribute *power10_pmu_caps_attrs[] =3D {
>>>> +       NULL
>>>> +};
>>>> +
>>>> +static struct attribute_group power10_pmu_caps_group =3D {
>>>> +       .name  =3D "caps",
>>>> +       .attrs =3D power10_pmu_caps_attrs,
>>>> +};
>>>> +
>>>> static const struct attribute_group *power10_pmu_attr_groups_dd1[] =
=3D {
>>>>      &power10_pmu_format_group,
>>>>      &power10_pmu_events_group_dd1,
>>>> @@ -267,6 +276,7 @@ static const struct attribute_group =
*power10_pmu_attr_groups_dd1[] =3D {
>>>> static const struct attribute_group *power10_pmu_attr_groups[] =3D =
{
>>>>      &power10_pmu_format_group,
>>>>      &power10_pmu_events_group,
>>>> +       &power10_pmu_caps_group,
>>>>      NULL,
>>>> };
>>>>=20
>>>> 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 =3D {
>>>>      .attrs =3D power8_events_attr,
>>>> };
>>>>=20
>>>> +static struct attribute *power8_pmu_caps_attrs[] =3D {
>>>> +       NULL
>>>> +};
>>>> +
>>>> +static struct attribute_group power8_pmu_caps_group =3D {
>>>> +       .name  =3D "caps",
>>>> +       .attrs =3D power8_pmu_caps_attrs,
>>>> +};
>>>> +
>>>> static const struct attribute_group *power8_pmu_attr_groups[] =3D {
>>>>      &isa207_pmu_format_group,
>>>>      &power8_pmu_events_group,
>>>> +       &power8_pmu_caps_group,
>>>>      NULL,
>>>> };
>>>>=20
>>>> 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 =3D {
>>>>      .attrs =3D power9_pmu_format_attr,
>>>> };
>>>>=20
>>>> +static struct attribute *power9_pmu_caps_attrs[] =3D {
>>>> +       NULL
>>>> +};
>>>> +
>>>> +static struct attribute_group power9_pmu_caps_group =3D {
>>>> +       .name  =3D "caps",
>>>> +       .attrs =3D power9_pmu_caps_attrs,
>>>> +};
>>>> +
>>>> static const struct attribute_group *power9_pmu_attr_groups[] =3D {
>>>>      &power9_pmu_format_group,
>>>>      &power9_pmu_events_group,
>>>> +       &power9_pmu_caps_group,
>>>>      NULL,
>>>> };
>>>>=20
>>>> --
>>>> 2.31.1