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.

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