Re: Again: Uniques in GHC

On Tue, Oct 7, 2014 at 11:26 AM, wrote:

Wait, wait, wait! I wasn't talking about a parallel *runtime*. Nothing changes there. All I'm talking about is something that is a very old issue that never got added / solved / resolved. Somewhere on the commentary, or the mailing list, I seem to recall that the generation of Uniques was the bottleneck for the parallelisation of GHC *Itself*. It's about having a compiler using multiple threads and says nothing about programs coming out of it.

OK, cool. Just making sure. :)

I'm all with you on embedded processors and that kind of stuff, but I don't see a pressing need to compile *on* them. Isn't all ARM-stuff assuming cross-compilation?

No, not all ARM builds assume cross compilation. In fact, if you want a fully working GHC, cross compilation is impossible: you cannot cross compile GHCi, meaning you can't use Template Haskell (as well as some of the linker features, I believe). However, I don't think this change impacts building GHC at all, since we get parallelism through 'make', not through GHC itself (and on low-end systems, parallelism in the build system is crucial and really necessary.) So I assume your change would mean 'ghc -j' would not work for 32bit. I still consider this a big limitation, one which is only due to an implementation detail. But we need to confirm this will actually fix any bottlenecks first though before getting to that point.

Ph.

________________________________________ From: mad.one@gmail.com on behalf of Austin Seipp Sent: 07 October 2014 17:46 To: Holzenspies, P.K.F. (EWI) Cc: ghc-devs@haskell.org Subject: Re: Again: Uniques in GHC

On Tue, Oct 7, 2014 at 1:32 AM, wrote:

...

Yes, this approach to a parallel GHC would only work on 64-bit machines. The idea is, I guess, that we're not going to see a massive demand for parallel GHC running on multi-core 32-bit systems. In other words; 32-bit systems wouldn't get a parallel GHC.

Let me make sure I'm understanding this correctly: in this particular proposed solution, the side effect would be that we no longer have a capable 32bit runtime which supports multicore parallelism?

Sorry, but I'm afraid this approach is pretty much unacceptable IMO, for precisely the reason outlined in your last sentence. 32bit systems are surprisingly commen. I have several multicore 32bit ARMv7 machines on my desk right now, for example. And there are a lot more of those floating around than you might think.

If that's the 'cure', I think I (and other users) would consider it far worse than the disease.

...

Regards, Philip

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-- Regards,

Austin Seipp, Haskell Consultant Well-Typed LLP, http://www.well-typed.com/

-- Regards, Austin Seipp, Haskell Consultant Well-Typed LLP, http://www.well-typed.com/