The document discusses techniques for measuring pipeline performance and time profiling in GStreamer, emphasizing the importance of measurement for effective optimization. It outlines various tools available for performance analysis, such as gst-top and gst-instrument, and highlights challenges related to tracing and CPU time measurement. The speaker concludes by inviting questions from the audience.

1. GStreamer Conference 2015
Simple techniques of pipeline performance
measurements and time profiling of individual
elements
Kyrylo Polezhaiev <kirushyk@gmail.com>
github.com/kirushyk
twitter.com/kirushyk

2. Why it is important to avoid extra work?
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Less hot laptop
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Longer battery live
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Smaller latency
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More users can be served simultaneously

3. Optimizations
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There is a way to improve performance: to do optimizations.
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This speech is not about optimizations.
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You can not optimize what you can not measure.
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You need to know what to focus on.

4. 1 a = get_current_time ();
2 foo ();
3 b = get_current_time ();
4 wasted_time = b – a;

5. 1 a = get_current_thread_time ();
2 foo ();
3 b = get_current_thread_time ();
4 spent_time = b – a;

6. 1 void foo () {
2 foo_stuff ();
3 }
4 void bar () {
5 bar_stuff ();
6 foo ();
7 }
8 void zozolala () {
9 bar ();
10 zozolala_stuff ();
11 }
Time of nested synchronous calls
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ΔT (foo) = ΔT (foo_stuff) + small overhead
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ΔT (bar) = ΔT (bar_stuff) + ΔT (foo) + small overhead
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ΔT (bar) = ΔT (bar_stuff) + ΔT (foo_stuff) + 2 small overheads
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ΔT (zozolala) = ΔT (zozolala_stuff) + ΔT (bar)
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ΔT (zozolala) = ΔT (zozolala_stuff) + ΔT (bar_stuff) + ΔT (foo_stuff)
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ΔT (bar_stuff) = ΔT (bar) – ΔT (foo) – small overhead

7. filesrc oggdemux vorbisdec audioconvert osxaudiosink

8. oggdemux → vorbisdec
vorbisdec →
audioconvert
audioconvert →
osxaudiosink
oggdemux

9. filesrc oggdemux vorbisdec audioconvert audiosink

10. GStreamer Instruments
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gst-top-1.0
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gst-instrument-1.0
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libgstintercept
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gst-report-1.0

11. gst-top-1.0
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Inspired by top and perf-top
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Prints elements sorted by CPU time spent
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Live mode isn't implemented yet

12. gst-instrument
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Tool with user interface to inspect dynamic performance graphs
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You can pick time interval to measure

13. Under the hood
libgstintercept (to be replaced soon) and gst-report-1.0

14. libgstintercept
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.so / .dylib to intercept GStreamer API calls
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Injected via LD_PRELOAD / DYLD_INSERT_LIBRARIES
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Dumps every pipeline to tracing file
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Will be replaced with new tracing infrastructure

15. API calls to intercept
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gst_element_change_state
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gst_pad_push
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gst_pad_push_list
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gst_pad_pull_range
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gst_pad_push_event
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gst_element_set_state

16. Problems with tracing
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Some elements (like x264enc) do not always use GstTasks and
creating their own threads.
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Inaccurate CPU time measurement: we need to take context
switch into account (to be fixed after moving to new GStreamer
tracing subsystem), have problems with upstack elements and
live pipeline.

17. gst-report-1.0
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Reads the trace file and creates performance report
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Can generate output in dot format

18. Thank you :-)
Questions?