perf_counter: add some comments

Add a few comments because I was forgetting what field what for what
functionality.

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: <20090408130409.036984214@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 6 insertions, 4 deletions

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 4809ae18a940..8bf764fc6220 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -344,10 +344,12 @@ struct file;
 
 struct perf_mmap_data {
         struct rcu_head                 rcu_head;
-        int                             nr_pages;
-        atomic_t                        wakeup;
-        atomic_t                        head;
-        atomic_t                        events;
+        int                             nr_pages;       /* nr of data pages  */
+
+        atomic_t                        wakeup;         /* POLL_ for wakeups */
+        atomic_t                        head;           /* write position    */
+        atomic_t                        events;         /* event limit       */
+
         struct perf_counter_mmap_page   *user_page;
         void                            *data_pages[0];
 };