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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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