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SubjectRe: [RFCv3 0/9] perf tool: parser generator for events parsing
On Wed, Jan 25, 2012 at 11:49:33AM +0100, Peter Zijlstra wrote:
> On Tue, 2012-01-24 at 16:53 -0800, Greg KH wrote:
>
> > Well, what's to keep someone from exploding one of those files to go
> > over the buffer size without knowing it?
>
> The content is known at compile time, we could put checks in. But yeah
> 4k isn't that much text..
>
> > Even after reading the above link, I can't really understand what this
> > is being used for. As it's sysfs files, why aren't Documentation/ABI/
> > files also being created with the patch explaining it all?
>
> Ah, yeah, documentation, wasn't that written in C :-)
>
> But fair enough... Anyway, the purpose is to describe the magic bits
> that go into perf_event_attr::config[012] for a particular pmu.
>
> Basically they're the 'hardware' bitmasks we want to export, so that
> userspace can deal with sane name/value pairs.
>
> > Again, if at all possible, sysfs should be one value per file. Please
> > NEVER create a sysfs file that requires a parser to determine what is
> > going on in it. It should be a simple 'read the value' type thing.
>
> The whole purpose was to drive a parser :-) Anyway, is:
> "config:0-7,32-35" acceptable for a single file?
>
> This means, the 'config' member of struct perf_event_attr bits 0-7,32-35
> form a bitfield whose name is then given by the filename that has this
> content.
>
> > So yes, multiple sysfs files do make sense, the resource load should be
> > almost non-existant for new ones.
>
> Surely all these attribute objects take more space than a few lines of
> text, but ok, I guess multiple files it is.
>

please check attached patch, would something like this be ok?

jirka
---
.../testing/sysfs-bus-event_source-devices-format | 14 ++++++++++++
include/linux/perf_event.h | 22 ++++++++++++++++++++
kernel/events/core.c | 22 ++++++++++++++++++++
3 files changed, 58 insertions(+), 0 deletions(-)
create mode 100644 Documentation/ABI/testing/sysfs-bus-event_source-devices-format

diff --git a/Documentation/ABI/testing/sysfs-bus-event_source-devices-format b/Documentation/ABI/testing/sysfs-bus-event_source-devices-format
new file mode 100644
index 0000000..5a15221
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-event_source-devices-format
@@ -0,0 +1,14 @@
+Where: /sys/bus/event_source/devices/<dev>/format
+Date: January 2012
+Kernel Version: 3.3
+Contact: Jiri Olsa <jolsa@redhat.com>
+Description:
+ Attribute group for 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.
+
+ Example: 'config1:1,6-10,44'
+ Defines contents of attribute that occupies bits 1,6-10,44 of
+ perf_event_attr::config1.
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 0b91db2..e2bf1c7 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -516,6 +516,7 @@ struct perf_guest_info_callbacks {
#include <linux/irq_work.h>
#include <linux/jump_label.h>
#include <linux/atomic.h>
+#include <linux/sysfs.h>
#include <asm/local.h>

#define PERF_MAX_STACK_DEPTH 255
@@ -626,6 +627,12 @@ struct pmu {
int task_ctx_nr;

/*
+ * True if the pmu defines its own set of format attributes within
+ * attr_groups. If false, default format attributes are used.
+ */
+ bool format_defined;
+
+ /*
* Fully disable/enable this PMU, can be used to protect from the PMI
* as well as for lazy/batch writing of the MSRs.
*/
@@ -1215,5 +1222,20 @@ do { \
register_cpu_notifier(&fn##_nb); \
} while (0)

+
+#define PMU_FORMAT_ATTR(_name, _format) \
+static ssize_t \
+pmu_format_attr_##_name##_show(struct device *dev, \
+ struct device_attribute *attr, \
+ char *page) \
+{ \
+ BUILD_BUG_ON(sizeof(_format) >= PAGE_SIZE); \
+ return sprintf(page, _format "\n"); \
+} \
+ \
+static struct device_attribute format_attr_##_name = \
+ __ATTR(_name, 0444, \
+ pmu_format_attr_##_name##_show, NULL)
+
#endif /* __KERNEL__ */
#endif /* _LINUX_PERF_EVENT_H */
diff --git a/kernel/events/core.c b/kernel/events/core.c
index de859fb..8d2d6f3 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5503,6 +5503,22 @@ static struct bus_type pmu_bus = {
.dev_attrs = pmu_dev_attrs,
};

+/* Default format attributes. */
+PMU_FORMAT_ATTR(config, "config:0-63");
+PMU_FORMAT_ATTR(config1, "config1:0-63");
+PMU_FORMAT_ATTR(config2, "config2:0-63");
+
+static struct attribute *format_attrs[] = {
+ &format_attr_config.attr,
+ &format_attr_config1.attr,
+ &format_attr_config2.attr,
+};
+
+static struct attribute_group format_attr_group = {
+ .name = "format",
+ .attrs = format_attrs,
+};
+
static void pmu_dev_release(struct device *dev)
{
kfree(dev);
@@ -5529,6 +5545,12 @@ static int pmu_dev_alloc(struct pmu *pmu)
if (ret)
goto free_dev;

+ if (!pmu->format_defined) {
+ ret = sysfs_create_group(&pmu->dev->kobj, &format_attr_group);
+ if (ret)
+ goto free_dev;
+ }
+
out:
return ret;

--
1.7.1


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