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Date:   Wed,  6 Dec 2017 15:32:55 -0800
        Kan Liang <>
Subject: [PATCH V2 0/8] 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 1-4: Modify perf_mmap__read_catchup and perf_mmap__read_backward.
	   Introduce perf_mmap__read_event
           Make generic code ready for overwrite mode
Patch 5-7: 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.
Patch 8: The latency could be still higher than refresh time in some
         extreme cases. Give user some hints to reduce the latency.

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 (8):
  perf tools: remove stale perf evlist mmap read for backward
  perf tools: rewrite perf mmap read for overwrite
  perf tools: reuse perf_mmap__read_catchup in perf_mmap__push
  perf tools: introduce perf_mmap__read_event
  perf top: check per event overwrite term
  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 |   9 +-
 tools/perf/ui/browsers/hists.c          |  12 ++-
 tools/perf/util/evlist.c                |  17 ----
 tools/perf/util/evlist.h                |   4 -
 tools/perf/util/mmap.c                  | 140 ++++++++++++++++++--------------
 tools/perf/util/mmap.h                  |  10 ++-
 7 files changed, 229 insertions(+), 102 deletions(-)


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