A fast, interactive web-based viewer for [sampling profiles][0]. An alternative viewer for [FlameGraphs][1]. Will happily display multi-megabyte profiles without crashing your browser.
Given raw profiling data, speedscope allows you to interactively explore the data to get insight into what's slow in your application, or allocating all the memory, or whatever data is represented in the profiling data.
Visit https://jlfwong.github.io/speedscope/, then either browse to find a profile file or drag-and-drop one onto the page. The profiles are not uploaded anywhere -- the application is totally in-browser.
Both the timeline format output by Chrome developers tools (https://developers.google.com/web/tools/chrome-devtools/evaluate-performance/reference#save) and the `.cpuprofile` format output are supported. The `.cpuprofile` format is useful for viewing flamecharts generated by Node.js applications:
If the `raw: true` flag is set when recording a dump, the resulting json dump can be imported into speedscope.
### `perf` and `DTrace`
If you process the output of `perf` or `DTrace` first with Brendan Gregg's `stackcollapse-*.pl` scripts (https://github.com/brendangregg/FlameGraph#2-fold-stacks), the result can be imported into speedscope.
## Importing via URL
To load a specific profile by URL, you can append a hash fragment like `#profileURL=[URL-encoded profile URL]&title=[URL-encoded custom title]`. Note that the server hosting the profile must have CORS configured to allow AJAX requests from speedscope.
In the "Time Order" view (the default), the stacks are ordered left-to-right in the same order as the occurred in the input file, which is usually going to be the chronological order they were recorded in. This view is most helpful for understand the behavior of an application over time, e.g. "first the data is fetched from the database, then the data is prepared for serialization, then the data is serialized to JSON". This is the only flame graph order supported by Chrome developer tools.
In all flamegraph views, the horizontal axis represents the "weight" of each stack (most commonly CPU time), and the vertical axis shows you the stack active at the time of the sample.
If you click on one of the frames, you'll be able to see summary statistics about it.
In the "Left Heavy" view, identical stacks are grouped together, regardless of whether they were recorded sequentially. Then, the stacks are sorted so that the heaviest stack for each parent is on the left -- hence "left heavy". This view is useful for understanding where all the time is going in situations where there are hundreds or thousands of function calls interleaved between other call stacks.
The Sandwich view is a table view in which you can find a list of all functions an their associated times. You can sort by self time or total time.
It's called "Sandwich" view because if you select one of the rows in the table, you can see flamegraphs for all the callers and callees of the selected
