Parallel --make (GHC build times on newer MacBook Pros?)

Brandon Moore brandon_m_moore at
Sat Aug 27 05:25:00 CEST 2011

> From: Evan Laforge <qdunkan at>

> Sent: Friday, August 26, 2011 6:35 PM
> Subject: Re: GHC build times on newer MacBook Pros?
> On Tue, Aug 23, 2011 at 10:24 AM, David Terei <davidterei at> 
> wrote:
>>  I have a 16 core machine at work (with 48GB of ram, a perk of the job
>>  :)). GHC can saturate them all. Can validate GHC in well under 10
>>  minutes on it.
> To wander a bit from the topic, when I first saw this I thought "wow,
> ghc builds in parallel now, I want that" but then I realized it's
> because ghc itself uses make, not --make.  --make's automatic
> dependencies are convenient, but figuring out dependencies on every
> build and not being parallel means make should be a lot faster.  Also,
> --make doesn't understand the hsc->hs link, so in practice I have to
> do a fair amount of manual dependencies anyway.  So it inspired me to
> try to switch from --make to make for my own project.

I'm confused by this as well. Parallelizing --make was one of the
first case studies in the smp runtime paper, section 7 in
Haskell on a Shared-Memory Multiprocessor

There's also a trac ticket a vague comment that the patch from the paper
"almost certainly isn't ready for prime time",
but I haven't
seen any description of specific problems.


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