perf_counter: Add PERF_EVENT_READ

Provide a read() like event which can be used to log the
counter value at specific sites such as child->parent
folding on exit.

In order to be useful, we log the counter parent ID, not the
actual counter ID, since userspace can only relate parent
IDs to perf_counter_attr constructs.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 12 insertions, 0 deletions

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index bcbf1c43ed42..6a384f04755a 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -335,6 +335,18 @@ enum perf_event_type {
         PERF_EVENT_FORK                 = 7,
 
         /*
+         * struct {
+         *      struct perf_event_header        header;
+         *      u32                             pid, tid;
+         *      u64                             value;
+         *      { u64           time_enabled;   } && PERF_FORMAT_ENABLED
+         *      { u64           time_running;   } && PERF_FORMAT_RUNNING
+         *      { u64           parent_id;      } && PERF_FORMAT_ID
+         * };
+         */
+        PERF_EVENT_READ                 = 8,
+
+        /*
          * When header.misc & PERF_EVENT_MISC_OVERFLOW the event_type field
          * will be PERF_SAMPLE_*
          *