perf_counter: PERF_SAMPLE_ID and inherited counters

Anton noted that for inherited counters the counter-id as provided by
PERF_SAMPLE_ID isn't mappable to the id found through PERF_RECORD_ID
because each inherited counter gets its own id.

His suggestion was to always return the parent counter id, since that
is the primary counter id as exposed. However, these inherited
counters have a unique identifier so that events like
PERF_EVENT_PERIOD and PERF_EVENT_THROTTLE can be specific about which
counter gets modified, which is important when trying to normalize the
sample streams.

This patch removes PERF_EVENT_PERIOD in favour of PERF_SAMPLE_PERIOD,
which is more useful anyway, since changing periods became a lot more
common than initially thought -- rendering PERF_EVENT_PERIOD the less
useful solution (also, PERF_SAMPLE_PERIOD reports the more accurate
value, since it reports the value used to trigger the overflow,
whereas PERF_EVENT_PERIOD simply reports the requested period changed,
which might only take effect on the next cycle).

This still leaves us PERF_EVENT_THROTTLE to consider, but since that
_should_ be a rare occurrence, and linking it to a primary id is the
most useful bit to diagnose the problem, we introduce a
PERF_SAMPLE_STREAM_ID, for those few cases where the full
reconstruction is important.

[Does change the ABI a little, but I see no other way out]

Suggested-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1248095846.15751.8781.camel@twins>

1 files changed, 4 insertions, 11 deletions

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 5e970c7d3fd5..bd15d7a5f5ce 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -120,8 +120,9 @@ enum perf_counter_sample_format {
         PERF_SAMPLE_ID                          = 1U << 6,
         PERF_SAMPLE_CPU                         = 1U << 7,
         PERF_SAMPLE_PERIOD                      = 1U << 8,
+        PERF_SAMPLE_STREAM_ID                   = 1U << 9,
 
-        PERF_SAMPLE_MAX = 1U << 9,              /* non-ABI */
+        PERF_SAMPLE_MAX = 1U << 10,             /* non-ABI */
 };
 
 /*
@@ -312,16 +313,7 @@ enum perf_event_type {
          *      struct perf_event_header        header;
          *      u64                             time;
          *      u64                             id;
-         *      u64                             sample_period;
-         * };
-         */
-        PERF_EVENT_PERIOD               = 4,
-
-        /*
-         * struct {
-         *      struct perf_event_header        header;
-         *      u64                             time;
-         *      u64                             id;
+         *      u64                             stream_id;
          * };
          */
         PERF_EVENT_THROTTLE             = 5,
@@ -356,6 +348,7 @@ enum perf_event_type {
          *      { u64                   time;     } && PERF_SAMPLE_TIME
          *      { u64                   addr;     } && PERF_SAMPLE_ADDR
          *      { u64                   id;       } && PERF_SAMPLE_ID
+         *      { u64                   stream_id;} && PERF_SAMPLE_STREAM_ID
          *      { u32                   cpu, res; } && PERF_SAMPLE_CPU
          *      { u64                   period;   } && PERF_SAMPLE_PERIOD
          *