Question: what are the time units?

[jurc192]

I profiled a python program with py-spy and am visualizing the results on www.speedscope.app.
What are the units of time, displayed at the timeline? (time order view)
What about the bottom right box w/ "This instance" and "All instances"? What is the meaning of those numbers?
Thanks for help :)

[bjorn3]

py-spy uses samples as unit: https://github.com/benfred/py-spy/blob/0a409aa57f28fccfb0d94a8d2a16b2ed0d6c42d3/src/speedscope.rs#L143 py-spy is a sampling profiler, which means that it samples the current stack every so often. The default sample rate is 100Hz: https://github.com/benfred/py-spy/blob/fedd53bd799efdac33d5a41ad56b1bb8047684b4/src/config.rs#L83 It is possible for samples to be taken later than that though.

[jlfwong]

FWIW, speedscope's file format supports specifying the time unit:

speedscope/src/lib/file-format-spec.ts

Lines 64 to 65 in 069c019

	// Unit which all value are specified using in the profile.
	unit: ValueUnit

So py-spy could specify this by taking into account the sampling rate and make it easier to read in the resulting profiles

[benfred]

thanks for the suggestion @jlfwong - I've created an issue in py-spy to track adding ValueUnit to py-spy profiles benfred/py-spy#294