perf_counter: comment the perf_event_type stuff

Describe the event format.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
LKML-Reference: <20090406094518.211174347@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 32 insertions, 0 deletions

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index ef4dcbff75ab..81220188d058 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -208,6 +208,20 @@ struct perf_event_header {
 
 enum perf_event_type {
 
+        /*
+         * The MMAP events record the PROT_EXEC mappings so that we can
+         * correlate userspace IPs to code. They have the following structure:
+         *
+         * struct {
+         *      struct perf_event_header        header;
+         *
+         *      u32                             pid, tid;
+         *      u64                             addr;
+         *      u64                             len;
+         *      u64                             pgoff;
+         *      char                            filename[];
+         * };
+         */
         PERF_EVENT_MMAP                 = 1,
         PERF_EVENT_MUNMAP               = 2,
 
@@ -217,6 +231,24 @@ enum perf_event_type {
          *
          * These events will have types of the form:
          *   PERF_EVENT_COUNTER_OVERFLOW { | __PERF_EVENT_* } *
+         *
+         * struct {
+         *      struct perf_event_header        header;
+         *
+         *      { u64                   ip;       } && __PERF_EVENT_IP
+         *      { u32                   pid, tid; } && __PERF_EVENT_TID
+         *
+         *      { u64                   nr;
+         *        { u64 event, val; }   cnt[nr];  } && __PERF_EVENT_GROUP
+         *
+         *      { u16                   nr,
+         *                              hv,
+         *                              kernel,
+         *                              user;
+         *        u64                   ips[nr];  } && __PERF_EVENT_CALLCHAIN
+         *
+         *      { u64                   time;     } && __PERF_EVENT_TIME
+         * };
          */
         PERF_EVENT_COUNTER_OVERFLOW     = 1UL << 31,
         __PERF_EVENT_IP                 = PERF_RECORD_IP,