perf_counter: uncouple data_head updates from wakeups

Keep data_head up-to-date irrespective of notifications. This fixes
the case where you disable a counter and don't get a notification for
the last few pending events, and it also allows polling usage.

[ Impact: increase precision of perfcounter mmap-ed fields ]

Suggested-by: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <20090505155436.925084300@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 3 insertions, 1 deletions

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index a356fa69796c..17b63105f2aa 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -362,9 +362,11 @@ struct perf_mmap_data {
         atomic_t                        head;           /* write position    */
         atomic_t                        events;         /* event limit       */
 
-        atomic_t                        wakeup_head;    /* completed head    */
+        atomic_t                        done_head;      /* completed head    */
         atomic_t                        lock;           /* concurrent writes */
 
+        atomic_t                        wakeup;         /* needs a wakeup    */
+
         struct perf_counter_mmap_page   *user_page;
         void                            *data_pages[0];
 };