Merge tag 'perf-core-for-mingo-4.20-20180919' of git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux into perf/core

Pull perf/core improvements and fixes from Arnaldo Carvalho de Melo:

perf test improvements:

- Add watchpoint entry (Ravi Bangoria)

Build fixes:

- Initialize perf_data_file fd field to fix building the CTF (trace format)
  converter with with gcc 4.8.4 on Ubuntu 14.04 (Jérémie Galarneau)

- Use -Wno-redundant-decls to build with PYTHON=python3 to
  build the python binding, fixing the build in systems such
  as Clear Linux (Arnaldo Carvalho de Melo)

Hardware tracing improvements:

- Suppress AUX/OVERWRITE records (Alexander Shishkin)

Infrastructure changes:

- Adopt PTR_ERR_OR_ZERO from the kernel and use it in
  the bpf-loader instead of open coded equivalent (Ding Xiang)

- Improve the event ordering code to make it clear and fix
  a bug related to freeing of events when using pipe mode
  from 'record' to 'inject' (Jiri Olsa)

- Some prep work to facilitate per-cpu threads to write
  record data to per-cpu files (Jiri Olsa)

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 12 insertions, 2 deletions

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 5d3cf407e374..4a9937076331 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -459,10 +459,20 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size)
 	if (size || handle->aux_flags) {
 		/*
 		 * Only send RECORD_AUX if we have something useful to communicate
+		 *
+		 * Note: the OVERWRITE records by themselves are not considered
+		 * useful, as they don't communicate any *new* information,
+		 * aside from the short-lived offset, that becomes history at
+		 * the next event sched-in and therefore isn't useful.
+		 * The userspace that needs to copy out AUX data in overwrite
+		 * mode should know to use user_page::aux_head for the actual
+		 * offset. So, from now on we don't output AUX records that
+		 * have *only* OVERWRITE flag set.
 		 */
 
-		perf_event_aux_event(handle->event, aux_head, size,
-		                     handle->aux_flags);
+		if (handle->aux_flags & ~(u64)PERF_AUX_FLAG_OVERWRITE)
+			perf_event_aux_event(handle->event, aux_head, size,
+			                     handle->aux_flags);
 	}
 
 	rb->user_page->aux_head = rb->aux_head;