On 06-May-2022, at 6:55 PM, Michael Ellerman [off-list ref] wrote:

Hi Athira,

Some comments below :)

Athira Rajeev [off-list ref] writes:

quoted

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.

Is there precedent for adding a "caps" directory? ie. do other PMUs on
other architectures already do that?

Hi Michael,

Thanks for the review comments.

Yes, There are other PMU’s on other architectures already having “caps” support.
I will add them in changelog for reference in V2.

Is there precedent for adding "pmu_name"?

I don't see any mention of them in Documentation/ABI anywhere.

If we're the first to do that we should add it to the documentation.

As this would set a precedent for other PMUs, please Cc the perf
maintainers on v2.

quoted

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.

Add a caps directory to /sys/bus/event_source/devices/cpu/
for power8, power9, power10 and generic compat PMU.

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 <redacted>
Reviewed-by: Madhavan Srinivasan <maddy@linux.ibm.com>
---
arch/powerpc/perf/generic-compat-pmu.c | 20 ++++++++++++++++++++
arch/powerpc/perf/power10-pmu.c        | 20 ++++++++++++++++++++
arch/powerpc/perf/power8-pmu.c         | 20 ++++++++++++++++++++
arch/powerpc/perf/power9-pmu.c         | 20 ++++++++++++++++++++
4 files changed, 80 insertions(+)

diff --git a/arch/powerpc/perf/generic-compat-pmu.c b/arch/powerpc/perf/generic-compat-pmu.c
index f3db88aee4dd..7b5fe2d89007 100644
--- a/arch/powerpc/perf/generic-compat-pmu.c
+++ b/arch/powerpc/perf/generic-compat-pmu.c

@@ -151,9 +151,29 @@ static const struct attribute_group generic_compat_pmu_format_group = {

	.attrs = generic_compat_pmu_format_attr,
};

+static ssize_t pmu_name_show(struct device *cdev,
+		struct device_attribute *attr,
+		char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "generic_compat_pmu");
+}

That's not a great name, now that it's exposed to userspace.

For starters it's only generic on Book3S, and if you look at
init_generic_compat_pmu() it's really a "ISA >= v3.0 fallback PMU" - or
something like that.

quoted

+static DEVICE_ATTR_RO(pmu_name);
+
+static struct attribute *generic_compat_pmu_caps_attrs[] = {
+	&dev_attr_pmu_name.attr,
+	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 d3398100a60f..a622ff783719 100644
--- a/arch/powerpc/perf/power10-pmu.c
+++ b/arch/powerpc/perf/power10-pmu.c

@@ -258,6 +258,25 @@ static const struct attribute_group power10_pmu_format_group = {

	.attrs = power10_pmu_format_attr,
};

+static ssize_t pmu_name_show(struct device *cdev,
+		struct device_attribute *attr,
+		char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "power10");

I believe that should use sysfs_emit().

Sure will change this.

quoted

+}
+
+static DEVICE_ATTR_RO(pmu_name);
+
+static struct attribute *power10_pmu_caps_attrs[] = {
+	&dev_attr_pmu_name.attr,
+	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 +286,7 @@ 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,
};

There's a lot of boiler plate repeated for each PMU.

We already have power_pmu->name, can we use that and make the show
function generic at least in core-book3s.c ?

Sure, I will rework on V2 to make the show function generic in core-book3s.
For the Generic Compat PMU, now that I am going to use show function from core-book3s, the
name exposed will be that of power_pmu->name

Thanks
Athira 

cheers