buying new hardware; want fast validate
duncan.coutts at worc.ox.ac.uk
Wed Apr 30 21:42:58 EDT 2008
On Wed, 2008-04-30 at 21:01 -0400, Norman Ramsey wrote:
> Dear Fellow GHC Hackers,
> I'll be buying new computers soon, and right now the only thing I do
> for which computer performance is a problem is GHC hacking---especially
> running 'validate'. I've got a good performance boost on my current
> machine by using two SATA drives striped in a RAID-0 configuration.
> I'm wondering what other tricks may be warranted. Specifically
> I'm interested in answers to the following questions:
> 1. How much benefit does one get from four cores versus two?
> I know that the build process runs in parallel thanks to
> make -j, but I don't know how much parallelism is available
> in the testing part. Maybe somebody who already has
> quad core can compare and let us know the results?
I recently got a quad core amd64 and I run linux. I noticed from the
system monitor graphs that not that much of the build process can use
many cores. I was using make -j5.
The one bit that really does benefit is building the ghc compiler
itself. That can make full use of all 4 cores for an extended period.
The ./configure step is painfully serial and building the early tools
and the libraries is rather serial too. There are lots of little changes
here that we could do to make it more parallel. One example is that we
link 20 copies of Setup.hs rather than reusing one copy. Linking is very
In principle the test suite should be possible to parallelise but I
don't know much about python and parallelism.
So given the price difference between dual and quad cores and the
opportunities for further parallelism I think it's worth going for quad.
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