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authorLinus Torvalds <torvalds@linux-foundation.org>2013-11-01 23:54:51 +0400
committerLinus Torvalds <torvalds@linux-foundation.org>2013-11-01 23:54:51 +0400
commit9581b7d2689ad9a0a20ddaec0427b46ad774585b (patch)
treef2eb9c9e4f2066c2ff1a7a3853ee6231ef879c11 /include
parent9119e33e507d3b8fe234f2c2bafd3199ea2e883b (diff)
parente8a923cc1fff6e627f906655ad52ee694ef2f6d7 (diff)
downloadlinux-9581b7d2689ad9a0a20ddaec0427b46ad774585b.tar.xz
Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull perf fixes from Ingo Molnar: "Two fixes: - Fix 'NMI handler took too long to run' false positives [ Genuine NMI overhead speedups will come for v3.13, this commit only fixes a measurement bug ] - Fix perf ring-buffer missed barrier causing (rare) ring-buffer data corruption on ppc64" * 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: perf/x86: Fix NMI measurements perf: Fix perf ring buffer memory ordering
Diffstat (limited to 'include')
-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 009a655a5d35..2fc1602e23bb 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -456,13 +456,15 @@ 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 */