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74 lines
2.7 KiB
74 lines
2.7 KiB
# Perfetto UI
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[Perfetto UI](https://ui.perfetto.dev) enables you to view and analyze traces in
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the browser. It supports several different tracing formats, including the
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perfetto proto trace format and the legacy json trace format.
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## UI Tips and Tricks
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### Debug Slices
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Sometimes you may want to insert some fake slices into the timeline to help
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with your understanding of the data. You can do so by inserting rows into a
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magic `debug_slices` table.
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`debug_slices` table has five columns:
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* `id` (integer) [optional] If present, Perfetto UI will use it as slice id to
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open the details panel when you click on the slices.
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* `name` (string) [optional] The displayed slice title.
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* `ts` (integer) [required] Start of the slice, in nanoseconds.
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* `dur` (integer) [required] Duration of the slice, in nanoseconds. Determines
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slice width.
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* `depth` (integer) [optional] The row at which the slice is drawn. Depth 0 is
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the first row.
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You can open the debug track by going to the "Sample queries" menu on the
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left, and clicking "Show Debug Track". A debug slice track will become pinned to
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the top and will initially be empty. After you insert slices in the
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`debug_slices` table, you can click the reload button on the track to refresh
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the information shown in that track.
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Here is a simple example with random slices to illustrate the use:
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```sql
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CREATE VIEW rand_slices AS SELECT * FROM SLICE
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ORDER BY RANDOM() LIMIT 2000;
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INSERT INTO debug_slices(id, name, ts, dur, depth)
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SELECT id, name, ts, dur, depth FROM RAND_SLICES;
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```
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After you click the reload button, you should see the slices in the debug track.
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Once you're done, you can click the X button to hide the track, and you can
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clear the `debug_slices` table (`DELETE FROM debug_slices`) to clear the track.
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A more interesting example is seeing RAIL modes in chrome traces:
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```sql
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SELECT RUN_METRIC('chrome/rail_modes.sql');
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-- Depth 0 is the unified RAIL Mode
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INSERT INTO debug_slices
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SELECT NULL, rail_mode, ts, dur, 0 FROM combined_overall_rail_slices;
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-- Depth 2+ are for each Renderer process with depth 1 left blank
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INSERT INTO debug_slices
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SELECT NULL, short_name, ts, dur, depth + 1 FROM rail_mode_slices,
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(SELECT track_id, row_number() OVER () AS depth FROM
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(SELECT DISTINCT track_id FROM rail_mode_slices)) depth_map,
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rail_modes
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WHERE depth_map.track_id = rail_mode_slices.track_id
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AND rail_mode=rail_modes.mode;
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```
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This produces a visualization like this:
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Note: There is no equivalent debug counters feature yet, but the feature request
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is tracked on [b/168886909](http://b/168886909)).
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