hs-speedscope: Convert an eventlog into the speedscope json format

[ bsd3, development, library, program ] [ Propose Tags ]

Convert an eventlog into the speedscope json format. The interactive visualisation displays an approximate trace of the program and summary views akin to .prof files. There is also support for parallel programs, each capability is rendered in its own profile.

[Skip to Readme]


Maintainer's Corner

Package maintainers

For package maintainers and hackage trustees


Versions [RSS],, 0.2, 0.2.1
Change log CHANGELOG.md
Dependencies aeson (>=1.4), base (>= && <5), extra (>=1.6), ghc-events (>=0.13 && <0.16), hs-speedscope, optparse-applicative (>=0.15), text (>=1.2), vector (>=0.12) [details]
License BSD-3-Clause
Author Matthew Pickering
Maintainer matthewtpickering@gmail.com
Category Development
Source repo head: git clone https://github.com/mpickering/hs-speedscope.git
Uploaded by OliverCharles at 2020-12-19T10:01:14Z
Distributions NixOS:0.2.1
Executables hs-speedscope
Downloads 1176 total (15 in the last 30 days)
Rating (no votes yet) [estimated by Bayesian average]
Your Rating
  • λ
  • λ
  • λ
Status Docs available [build log]
Last success reported on 2020-12-19 [all 1 reports]

Readme for hs-speedscope-0.2.1

[back to package description]


hs-speedscope is a simple executable for converting an eventlog into a format suitable to load into speedscope.

WARNING: Only GHC 8.10 supports generating an eventlog with the correct events for this program to work.


  1. Create an eventlog which contains time profiling events by running your program with program +RTS -p -l-au.
  2. Run hs-speedscope on the resulting eventlog hs-speedscope program.eventlog.
  3. Load the resulting program.eventlog.json file into speedscope to visualise the profile.


cabal update
cabal install exe:hs-speedscope

This will install to cabal's per-user default location: ~/.cabal/bin/hs-speedscope.

Filtering an eventlog

It is sometimes useful to isolate a specific part of the sample, for example, when I was profiling ghcide, I want to isolate a single hover request.

The --start and --end options can be used to indicate which parts of the eventlog to keep. The filtering options look for messages inserted into the eventlog by traceMarker events.

  • No events before the first marker which matches the prefix given by --start will be included in the result
  • No events after the first marker which matches the prefix given by --end will be included in the result.

For example, the following invocation will filter the profile between the START and END markers.

hs-speedscope File.eventlog --start START --end END