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Subject[PATCH RFC V2 00/10] perf top optimization
From: Kan Liang <>

The patch series intends to fix the severe performance issue in
Knights Landing/Mill, when monitoring in heavy load system.
perf top costs a few minutes to show the result, which is
With the patch series applied, the latency will reduces to
several seconds.

machine__synthesize_threads and perf_top__mmap_read costs most of
the perf top time (> 99%).
Patch 1-9 do the optimization for machine__synthesize_threads.
Patch 10 does the optimization for perf_top__mmap_read.

Optimization for machine__synthesize_threads
- Multithreading the whole process.
- The threads number is set to the max online CPU# by default.
User can change the threads number through the new option.
- Introduces hashtable for machine threads to reduce the lock
- The optimization can also benefit other platforms and other
perf tools, like perf record. But this patch series doesn't
do the optimization for other tools. It can be done later
- With this optimization applied, there is a 1.56x speedup in
Knights Mill with heavy workload.

Optimization for perf_top__mmap_read
- switch back to overwrite mode
For non overwrite mode, it tries to read everything in the ring buffer
and does not check the messup. Once there are lots of samples delivered
shortly, the processing time could be very long.
Considering the real time requirement for perf top, it should switch
back to overwrite mode.
- With this optimization applied, there is a huge 53.8x speedup in
Knights Mill with heavy workload.
- With this optimization applied, the latency of perf_top__mmap_read is
less than the default perf top fresh time (2s) in Knights Mill with
heavy workload.

Here are perf top latency test result on Knights Mill and Skylake server

The heavy workload is to compile Linux kernel as below
"sudo nice make -j$(grep -c '^processor' /proc/cpuinfo)"
Then, "sudo perf top"

The latency period is the time between perf top launched and the first
profiling result shown.

- Latency on Knights Mill (272 CPUs)

Original(s) With patch(s) Speedup
272.68 16.48 16.54x

- Latency on Skylake server (192 CPUs)

Original(s) With patch(s) Speedup
12.28 2.96 4.15x

Changes since V1:
- Patch 1: machine threads and hashtable related renaming (Arnaldo)
- Patch 6: use a smaller locked section for comm_str__put
add a locked wrapper for comm_str__findnew (Arnaldo)

Kan Liang (10):
perf tools: hashtable for machine threads
perf tools: using scandir to replace readdir
petf tools: using comm_str to replace comm in hist_entry
petf tools: introduce a new function to set namespaces id
perf tools: lock to protect thread list
perf tools: lock to protect comm_str rb tree
perf tools: change machine comm_exec type to atomic
perf top: implement multithreading for perf_event__synthesize_threads
perf top: add option to set the number of thread for event synthesize
perf top: switch back to overwrite mode

tools/perf/builtin-kvm.c | 3 +-
tools/perf/builtin-record.c | 2 +-
tools/perf/builtin-top.c | 9 +-
tools/perf/builtin-trace.c | 21 +++--
tools/perf/tests/mmap-thread-lookup.c | 2 +-
tools/perf/ui/browsers/hists.c | 2 +-
tools/perf/util/comm.c | 18 +++-
tools/perf/util/event.c | 149 +++++++++++++++++++++++++-------
tools/perf/util/event.h | 14 ++-
tools/perf/util/evlist.c | 5 +-
tools/perf/util/hist.c | 11 +--
tools/perf/util/machine.c | 158 +++++++++++++++++++++-------------
tools/perf/util/machine.h | 34 ++++++--
tools/perf/util/rb_resort.h | 5 +-
tools/perf/util/sort.c | 8 +-
tools/perf/util/sort.h | 2 +-
tools/perf/util/thread.c | 68 ++++++++++++---
tools/perf/util/thread.h | 6 +-
tools/perf/util/top.h | 1 +
19 files changed, 376 insertions(+), 142 deletions(-)


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