Compilation time

Robin Palotai palotai.robin at
Tue Jul 4 07:29:12 UTC 2017

Note that Travis CI time is a sum of all operations, including
fetching/saving caches etc.

Opening the build log and looking for the compilation might be more
revealing. For example, 7.10 seems ~10 seconds, 8.2.1 seems ~50 seconds.

There are two issues I can see with this, that should be addressed by

1) The Travis CI build hosts might show varying performance across reruns
due to shared machines.

2) Tuning the RTS params when invoking GHC as a compiler can yield
significant benefits, at least on larger compilations (such as -A128m).

It would probably be doable to fetch a set of packages from *ackage and
build with various compilers under controlled circumstances?


2017-07-04 9:16 GMT+02:00 Deest, Gaël <gael.deest at>:

> Hi all,
> As you are probably well aware, GHC performance has been a growing concern
> over the last few years. Many Haskell programmers complain that build time
> has significantly increased over the last few releases. However, to our
> knowledge, there isn't much data available to substantiate this claim and
> the severity of these problems is not well known.
> That's why we would like to bring some anecdotal evidence to your
> attention that seems to indicate really major performance regressions. We
> stumbled upon the CI of the data-reify package, which is built against all
> GHC releases since 2010 :
> tl;dr: Build time has gone from 1 min 32s for GHC 7.0 to 4 min 35s for GHC
> 8.2. The 8.2 release alone seems to have increased compilation time by
> almost 2 minutes, with the current development branch bringing only minor
> performance improvements.
> Of course, this single data point is not sufficient to establish how
> severe and widespread these problems are. More data could probably be
> gathered from other packages. However, it certainly matches our
> (subjective) experience and we felt important to report it to you.
> Regards,
> --
> Gaël Deest
> Tweag I/O
> _______________________________________________
> ghc-devs mailing list
> ghc-devs at
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