Announcing Profiterole - GHC Profile Viewer

Summary: profiterole reformats GHC profile reports so they are easier to read.

Do you often work with GHC time profiling reports? Do you find them excessively long and hard to navigate? Profiterole reads standard GHC .prof files and generates both textual and HTML reports which are typically more than 10x smaller. As an example compare HLint profile input to HLint Profiterole output.

Usage

To run, first install (cabal update && cabal install profiterole), generate a GHC profile the normal way, then run:

profiterole myprogram.prof

Profiterole will generate myprogram.profiterole.txt and myprogram.profiterole.html - both contain the same information, but the HTML has hyperlinks. There are three columns of numbers:

• TOT is the total time spent in any item under this code, what GHC calls inherited time.
• INH is the total time spent in the items that Profiterole did not move out to the top level.
• IND is the individual time, just like GHC profiles.

For large programs, using +RTS -P (instead of the common -p) will give more accurate results.

How it works

Profiterole aims to make the profile shorter by combining common subtrees and lifting them to the root - e.g. if you call parseFile from 7 places in the code, instead of having 7 pieces of parseFile profiling, Profiterole will give you one. With only 1 place containing parseFile, it's easier to optimise parseFile, and it's easier to read the code calling it without getting lost in the internals.

How to profile

Given profile data, different ways of looking at it reveal different insights, and the ones discovered by Profiterole have definitely had value. I tend to use:

• I first use Profiteur to get an overall sense of where the time is going visually. Profiteur lets me orientate myself, but tends to be a little difficult to drill into the details and repeat experiments.
• I then use Profiterole to see if there were any repeated pieces of code Profiteur missed, and then dig into the details using Profiterole.
• Only if I'm really going into the details do I go to the GHC .prof output - it's pretty rare.