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authorIngo Molnar <mingo@kernel.org>2013-11-04 07:49:35 +0100
committerIngo Molnar <mingo@kernel.org>2013-11-04 07:49:35 +0100
commit2a3ede8cb2ddee5885518e4232aca13056f9a6e0 (patch)
tree79b2b4e060a97b1e7c60d58549f8c97cb15db5dd /include/uapi/linux/perf_event.h
parent0e73453e172aaa38fd59fd4d3fc589e8fc9b9a70 (diff)
parent215432ed30393ed4a8f77db0a1fe34523c48cdba (diff)
Merge branch 'perf/urgent' into perf/core to fix conflicts
Conflicts: tools/perf/bench/numa.c Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/uapi/linux/perf_event.h')
-rw-r--r--include/uapi/linux/perf_event.h12
1 files changed, 7 insertions, 5 deletions
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index da48837d617..e1802d6153a 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -479,13 +479,15 @@ struct perf_event_mmap_page {
/*
* Control data for the mmap() data buffer.
*
- * User-space reading the @data_head value should issue an rmb(), on
- * SMP capable platforms, after reading this value -- see
- * perf_event_wakeup().
+ * User-space reading the @data_head value should issue an smp_rmb(),
+ * after reading this value.
*
* When the mapping is PROT_WRITE the @data_tail value should be
- * written by userspace to reflect the last read data. In this case
- * the kernel will not over-write unread data.
+ * written by userspace to reflect the last read data, after issueing
+ * an smp_mb() to separate the data read from the ->data_tail store.
+ * In this case the kernel will not over-write unread data.
+ *
+ * See perf_output_put_handle() for the data ordering.
*/
__u64 data_head; /* head in the data section */
__u64 data_tail; /* user-space written tail */