Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Content-Type: text/plain;
        charset=us-ascii
Mime-Version: 1.0 (Mac OS X Mail 14.0 \(3654.120.0.1.13\))
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=fWN3Sgyp_hTyYvDrLrnr-7dj6ozERn0tDm5MrU2SEJ2Fg@mail.gmail.com>
Date:   Thu, 19 May 2022 16:58:58 +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
Content-Transfer-Encoding: quoted-printable
Message-Id: <4D9BD7B3-1FA0-4EFE-A7D9-75BBB84ED308@linux.vnet.ibm.com>
References: <20220518085502.6914-1-atrajeev@linux.vnet.ibm.com>
 <CAP-5=fWN3Sgyp_hTyYvDrLrnr-7dj6ozERn0tDm5MrU2SEJ2Fg@mail.gmail.com>
To:     Ian Rogers <irogers@google.com>
Precedence: bulk


> 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

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
>=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