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Date:   Thu, 21 Dec 2017 10:08:42 -0800
        Kan Liang <>
Subject: [PATCH V3 00/12] perf top overwrite mode

From: Kan Liang <>

perf_top__mmap_read has severe performance issue in
Knights Landing/Mill, when monitoring in heavy load system. It costs
several minutes to finish, which is unacceptable.

Currently, perf top is non overwrite mode. For non overwrite mode, it
tries to read everything in the ringbuffer and doesn't pause the
ringbuffer. Once there are lots of samples delivered persistently,
the processing time could be very long. Also, the latest samples could
be lost when the ringbuffer is full.

It's better to change it to overwrite mode, which takes a snapshot for
the system by pausing the ringbuffer and could significantly reducing
the processing time (from several minutes to several seconds).
Also, the overwrite mode always keep the latest samples.

Patch 1-7:  Introduce new interfaces for generic code to support
            overwrite mode for one by one event read.
            Discards stale interfaces.
            The patches can be merged separately.
Patch 8-12: Add overwrite support to perf top.
            Perf top should only support either overwrite or non-overwrite
            Switch default mode to overwrite mode
            If kernel doesn't support overwrite mode, fall back to
            non-overwrite mode.

Changes since V2:
 - Move duplicate 'map->prev' out of perf_mmap__read. Modify the
   perf_mmap__read_event accordingly.
 - Introduce new interface perf_mmap__read_init to calculate the ringbuffer
 - Check perf_missing_features.write_backward
 - Discard stale interfaces perf_mmap__read_backward and

Changes since V1:
 - New patches 4-6
 - Support both overwrite mode and non-overwrite mode.
   If kernel doesn't support default overwrite mode, fall back to
   non-overwrite mode.

Kan Liang (12):
  perf evlist: remove stale mmap read for backward
  perf mmap: factor out function to find ringbuffer position
  perf mmap: discard 'prev' in perf_mmap__read
  perf mmap: introduce perf_mmap__read_done
  perf mmap: introduce perf_mmap__read_event
  perf test: update mmap read functions for backward-ring-buffer test
  perf mmap: discard legacy interface for mmap read
  perf top: check per event overwrite term
  perf evsel: expose perf_missing_features.write_backward
  perf top: add overwrite fall back
  perf top: switch default mode to overwrite mode
  perf top: check the latency of perf_top__mmap_read

 tools/perf/builtin-top.c                | 139 +++++++++++++++++++++++++---
 tools/perf/tests/backward-ring-buffer.c |   7 +-
 tools/perf/ui/browsers/hists.c          |  12 ++-
 tools/perf/util/evlist.c                |  17 ----
 tools/perf/util/evlist.h                |   4 -
 tools/perf/util/evsel.c                 |   5 +
 tools/perf/util/evsel.h                 |   2 +
 tools/perf/util/mmap.c                  | 158 ++++++++++++++++++--------------
 tools/perf/util/mmap.h                  |  10 +-
 9 files changed, 244 insertions(+), 110 deletions(-)


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