[PATCH 08/16] perf, persistent: Exposing persistent events using sysfs

Jean Pihet
2014-04-07T15:08:47Z

From: Robert Richter <robert.richter@linaro.org>

Expose persistent events in the system to userland using sysfs. Perf
tools are able to read existing pmu events from sysfs. Now we use a
persistent pmu as an event container containing all registered
persistent events of the system. This patch adds dynamically
registration of persistent events to sysfs. E.g. something like this:

/sys/bus/event_source/devices/persistent/events/mce_record:persistent,config=106
/sys/bus/event_source/devices/persistent/format/persistent:attr5:23

Perf tools need to support the attr<num> syntax that is added in a
separate patch set. With it we are able to run perf tool commands to
read persistent events, e.g.:

# perf record -e persistent/mce_record/ sleep 10
# perf top -e persistent/mce_record/

[ Jiri: Document attr<index> syntax in sysfs ABI ]
[ Namhyung: Fix sysfs registration with lockdep enabled ]
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Robert Richter <robert.richter@linaro.org>
Signed-off-by: Robert Richter <rric@kernel.org>
Signed-off-by: Jean Pihet <jean.pihet@linaro.org>
---
.../testing/sysfs-bus-event_source-devices-format | 43 ++++++++++++----
kernel/events/persistent.c | 60 ++++++++++++++++++++++
2 files changed, 92 insertions(+), 11 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-bus-event_source-devices-format b/Documentation/ABI/testing/sysfs-bus-event_source-devices-format
index 77f47ff..744d53a 100644
--- a/Documentation/ABI/testing/sysfs-bus-event_source-devices-format
+++ b/Documentation/ABI/testing/sysfs-bus-event_source-devices-format
@@ -1,13 +1,14 @@
-Where: /sys/bus/event_source/devices/<dev>/format
+Where: /sys/bus/event_source/devices/<pmu>/format/<name>
Date: January 2012
-Kernel Version: 3.3
+Kernel Version: 3.3
+ 3.xx (added attr<index>:<bits>)
Contact: Jiri Olsa <jolsa@redhat.com>
-Description:
- Attribute group to describe the magic bits that go into
- perf_event_attr::config[012] for a particular pmu.
- Each attribute of this group defines the 'hardware' bitmask
- we want to export, so that userspace can deal with sane
- name/value pairs.
+
+Description: Define formats for bit ranges in perf_event_attr
+
+ Attribute group to describe the magic bits that go
+ into struct perf_event_attr for a particular pmu. Bit
+ range may be any bit mask of an u64 (bits 0 to 63).

Userspace must be prepared for the possibility that attributes
define overlapping bit ranges. For example:
@@ -15,6 +16,26 @@ Description:
attr2 = 'config:0-7'
attr3 = 'config:12-35'

- Example: 'config1:1,6-10,44'
- Defines contents of attribute that occupies bits 1,6-10,44 of
- perf_event_attr::config1.
+ Syntax Description
+
+ config[012]*:<bits> Each attribute of this group
+ defines the 'hardware' bitmask
+ we want to export, so that
+ userspace can deal with sane
+ name/value pairs.
+
+ attr<index>:<bits> Set any field of the event
+ attribute. The index is a
+ decimal number that specifies
+ the u64 value to be set within
+ struct perf_event_attr.
+
+ Examples:
+
+ 'config1:1,6-10,44' Defines contents of attribute
+ that occupies bits 1,6-10,44
+ of perf_event_attr::config1.
+
+ 'attr5:24' Define the persistent event
+ flag (bit 24 of the attribute
+ flags)
diff --git a/kernel/events/persistent.c b/kernel/events/persistent.c
index 6b039f5..6578acf 100644
--- a/kernel/events/persistent.c
+++ b/kernel/events/persistent.c
@@ -8,6 +8,7 @@
#define CPU_BUFFER_NR_PAGES ((512 * 1024) / PAGE_SIZE)

struct pevent {
+ struct perf_pmu_events_attr sysfs;
char *name;
int id;
};
@@ -119,6 +120,8 @@ static void persistent_event_close(int cpu, struct pevent *pevent)
persistent_event_release(event);
}

+static int pevent_sysfs_register(struct pevent *event);
+
static int __maybe_unused
persistent_open(char *name, struct perf_event_attr *attr, int nr_pages)
{
@@ -144,12 +147,18 @@ persistent_open(char *name, struct perf_event_attr *attr, int nr_pages)
goto fail;
}

+ pevent->sysfs.id = pevent->id;
+
for_each_possible_cpu(cpu) {
ret = persistent_event_open(cpu, pevent, attr, nr_pages);
if (ret)
goto fail;
}

+ ret = pevent_sysfs_register(pevent);
+ if (ret)
+ goto fail;
+
return 0;
fail:
for_each_possible_cpu(cpu)
@@ -223,10 +232,61 @@ static struct attribute_group persistent_format_group = {
.attrs = persistent_format_attrs,
};

+#define MAX_EVENTS 16
+
+static struct attribute *pevents_attr[MAX_EVENTS + 1] = { };
+
+static struct attribute_group pevents_group = {
+ .name = "events",
+ .attrs = pevents_attr,
+};
+
static const struct attribute_group *persistent_attr_groups[] = {
&persistent_format_group,
+ NULL, /* placeholder: &pevents_group */
NULL,
};
+#define EVENTS_GROUP_PTR (&persistent_attr_groups[1])
+
+static ssize_t pevent_sysfs_show(struct device *dev,
+ struct device_attribute *__attr, char *page)
+{
+ struct perf_pmu_events_attr *attr =
+ container_of(__attr, struct perf_pmu_events_attr, attr);
+ return sprintf(page, "persistent,config=%lld",
+ (unsigned long long)attr->id);
+}
+
+static int pevent_sysfs_register(struct pevent *pevent)
+{
+ struct perf_pmu_events_attr *sysfs = &pevent->sysfs;
+ struct attribute *attr = &sysfs->attr.attr;
+ struct device *dev = persistent_pmu.dev;
+ const struct attribute_group **group = EVENTS_GROUP_PTR;
+ int idx;
+
+ sysfs->id = pevent->id;
+ sysfs->attr = (struct device_attribute)
+ __ATTR(, 0444, pevent_sysfs_show, NULL);
+ attr->name = pevent->name;
+ sysfs_attr_init(attr);
+
+ /* add sysfs attr to events: */
+ for (idx = 0; idx < MAX_EVENTS; idx++) {
+ if (!cmpxchg(pevents_attr + idx, NULL, attr))
+ break;
+ }
+
+ if (idx >= MAX_EVENTS)
+ return -ENOSPC;
+ if (!idx)
+ *group = &pevents_group;
+ if (!dev)
+ return 0; /* sysfs not yet initialized */
+ if (idx)
+ return sysfs_add_file_to_group(&dev->kobj, attr, (*group)->name);
+ return sysfs_create_group(&persistent_pmu.dev->kobj, *group);
+}

static int persistent_pmu_init(struct perf_event *event)
{
--
1.7.11.7