[PATCH v3 21/23] perf: Allocate ring buffers for inherited per-task kernel events

Alexander Shishkin
2014-08-11T05:36:47Z

When a new event is inherited from a per-task kernel event that has a
ring buffer, allocate a new buffer for this event so that data from the
child task is collected and can later be retrieved for sample annotation
or whatnot.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
---
kernel/events/core.c | 9 +++++++++
kernel/events/internal.h | 11 +++++++++++
2 files changed, 20 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7a3ffda1c0..c2f02ea6d7 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7993,6 +7993,15 @@ inherit_event(struct perf_event *parent_event,
(void)perf_event_set_output(child_event, parent_event);

/*
+ * For per-task kernel events with ring buffers, set_output doesn't
+ * make sense, but we can allocate a new buffer here.
+ */
+ if (parent_event->cpu == -1 && kernel_rb_event(parent_event)) {
+ (void)rb_alloc_kernel(child_event, parent_event->rb->nr_pages,
+ parent_event->rb->aux_nr_pages);
+ }
+
+ /*
* Precalculate sample_data sizes
*/
perf_event__header_size(child_event);
diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index bb035dd645..b306bc9307 100644
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -120,6 +120,17 @@ static inline unsigned long perf_aux_size(struct ring_buffer *rb)
return rb->aux_nr_pages << PAGE_SHIFT;
}

+static inline bool kernel_rb_event(struct perf_event *event)
+{
+ /*
+ * Having a ring buffer and not being on any ring buffers' wakeup
+ * list means it was attached by rb_alloc_kernel() and not
+ * ring_buffer_attach(). It's the only case when these two
+ * conditions take place at the same time.
+ */
+ return event->rb && list_empty(&event->rb_entry);
+}
+
#define DEFINE_OUTPUT_COPY(func_name, memcpy_func) \
static inline unsigned long \
func_name(struct perf_output_handle *handle, \
--
2.1.0.rc1