perf: Add active_entry list head to struct perf_event

This patch adds a new field to the struct perf_event.
It is intended to be used to chain events which are
active (enabled). It helps in the hardware layer
for PMUs which do not have actual counter restrictions, i.e.,
free running read-only counters. Active events are chained
as opposed to being tracked via the counter they use.

To save space we use a union with hlist_entry as both
are mutually exclusive (suggested by Jiri Olsa).

Signed-off-by: Stephane Eranian <eranian@google.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: acme@redhat.com
Cc: jolsa@redhat.com
Cc: zheng.z.yan@intel.com
Cc: bp@alien8.de
Cc: maria.n.dimakopoulou@gmail.com
Link: http://lkml.kernel.org/r/1384275531-10892-2-git-send-email-eranian@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 2e069d1288df..8f4a70f2eca8 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -319,7 +319,10 @@ struct perf_event {
          */
         struct list_head                migrate_entry;
 
-        struct hlist_node               hlist_entry;
+        union {
+                struct hlist_node       hlist_entry;
+                struct list_head        active_entry;
+        };
         int                             nr_siblings;
         int                             group_flags;
         struct perf_event               *group_leader;