[I'll be the mentor for this GSoC project.] I used the MVar approach a while ago and so did Simon Marlow's original solution. Using MVars and Threads for this should scale well enough (1000s of modules) and be relatively straightforward. Error/exception handling could be a bit tricky, but you could use (or copy ideas from) the 'async' package to deal with that.
/ Thomas On 30 May 2013 18:51, Ryan Newton <[email protected]> wrote: > What's the plan for what control / synchronization structures you'll use in > part 2 of the plan to implement a parallel driver? > > Is the idea just to use an IO thread for each compile and block them on > MVars when they encounter dependencies? Or you can use a pool of worker > threads and a work queue, and only add modules to the work queue when all > their dependencies are met (limits memory use)... many options for executing > a task DAG. Fortunately the granularity is coarse. > > -Ryan > > > > On Sun, Apr 21, 2013 at 10:34 PM, Patrick Palka <[email protected]> > wrote: >> >> Good points. I did not take into account whether proposal #2 may be worth >> it in light of -fllvm. I suppose that even if the LLVM codegen is able to >> perform similar optimizations, it would still be beneficial to implement >> proposal #2 as a core-to-core pass because the transformations it performs >> would expose new information to subsequent core-to-core passes. Also, >> Haskell has different overflow rules than C does (whose rules I assume >> LLVM's optimizations are modeled from): In Haskell, integer overflow is >> undefined for all integral types, whereas in C it's only undefined for >> signed integral types. This limits the number of optimizations a C-based >> optimizer can perform on unsigned arithmetic. >> >> I'm not sure how I would break up the parallel compilation proposal into >> multiple self-contained units of work. I can only think of two units: making >> GHC thread safe, and writing the new parallel compilation driver. Other >> incidental units may come up during development (e.g. parallel compilation >> might exacerbate #4012), but I still feel that three months of full time >> work is ample time to complete the project, especially with existing >> familiarity with the code base. >> >> Thanks for the feedback. >> >> >> On Sun, Apr 21, 2013 at 5:55 PM, Carter Schonwald >> <[email protected]> wrote: >>> >>> Hey Patrick, >>> both are excellent ideas for work that would be really valuable for the >>> community! >>> (independent of whether or not they can be made into GSOC sided chunks ) >>> >>> ------- >>> I'm actually hoping to invest some time this summer investigating >>> improving the numerics optimization story in ghc. This is in large part >>> because I'm writing LOTs of numeric codes in haskell presently (hopefully on >>> track to make some available to the community ). >>> >>> That said, its not entirely obvious (at least to me) what a tractable >>> focused GSOC sized subset of the numerics optimization improvement would be, >>> and that would have to also be a subset that has real performance impact and >>> doesn't benefit from eg using -fllvm rather than -fasm . >>> --------- >>> >>> For helping pave the way to better parallel builds, what are some self >>> contained units of work on ghc (or related work on cabal) that might be >>> tractable over a summer? If you can put together a clear roadmap of "work >>> chunks" that are tractable over the course of the summer, I'd favor choosing >>> that work, especially if you can give a clear outline of the plan per chunk >>> and how to evaluate the success of each unit of work. >>> >>> basically: while both are high value projects, helping improve the >>> parallel build tooling (whether in performance or correctness or both!) has >>> a more obvious scope of community impact, and if you can layout a clear plan >>> of work that GHC folks agree with and seems doable, i'd favor that project >>> :) >>> >>> hope this feedback helps you sort out project ideas >>> >>> cheers >>> -Carter >>> >>> >>> >>> >>> On Sun, Apr 21, 2013 at 12:20 PM, Patrick Palka <[email protected]> >>> wrote: >>>> >>>> Hi, >>>> >>>> I'm interested in participating in the GSoC by improving GHC with one of >>>> these two features: >>>> >>>> 1) Implement native support for compiling modules in parallel (see >>>> #910). This will involve making the compilation pipeline thread-safe, >>>> implementing the logic for building modules in parallel (with an emphasis >>>> on >>>> keeping compiler output deterministic), and lots of testing and >>>> benchmarking. Being able to seamlessly build modules in parallel will >>>> shorten the time it takes to recompile a project and will therefore improve >>>> the life of every GHC user. >>>> >>>> 2) Improve existing constant folding, strength reduction and peephole >>>> optimizations on arithmetic and logical expressions, and optionally >>>> implement a core-to-core pass for optimizing nested comparisons (relevant >>>> tickets include #2132,#5615,#4101). GHC currently performs some of these >>>> simplifications (via its BuiltinRule framework), but there is a lot of room >>>> for improvement. For instance, the core for this snippet is essentially >>>> identical to the Haskell source: >>>> >>>> foo :: Int -> Int -> Int -> Int >>>> foo a b c = 10*((b+7+a+12+b+9)+4) + 5*(a+7+b+12+a+9) + 7 + b + c >>>> >>>> Yet the RHS is actually equivalent to >>>> >>>> 20*a + 26*b + c + 467 >>>> >>>> And: >>>> >>>> bar :: Int -> Int -> Int >>>> bar a b = a + b - a - b -- the RHS is should be optimized away to 0 >>>> >>>> Other optimizations include: multiplication and division by powers of >>>> two should be converted to shifts; multiple plusAddr calls with constant >>>> operands should be coalesced into a single plusAddr call; floating point >>>> functions should be constant folded, etc.. >>>> >>>> GHC should be able to perform all these algebraic simplifications. Of >>>> course, emphasis should be placed on the correctness of such >>>> transformations. A flag for performing unsafe optimizations like assuming >>>> floating point arithmetic is associative and distributive should be added. >>>> This proposal will benefit anybody writing or using numerically intensive >>>> code. >>>> >>>> >>>> I'm wondering what the community thinks of these projects. Which project >>>> is a better fit for GSoC, or are both a good fit? Is a mentor willing to >>>> supervise one of these projects? >>>> >>>> Thanks for your time. >>>> Patrick >>>> >>>> (A little about myself: I'm a Mathematics student in the US, and I've >>>> been programming in Haskell for about 3.5 years. Having a keen interest in >>>> Haskell and compilers, I began studying the GHC source about 1 year ago and >>>> I've since gotten a good understanding of its internals, contributing a few >>>> patches along the way.) >>>> >>>> >>>> _______________________________________________ >>>> Haskell-Cafe mailing list >>>> [email protected] >>>> http://www.haskell.org/mailman/listinfo/haskell-cafe >>>> >>> >> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> [email protected] >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > _______________________________________________ Haskell-Cafe mailing list [email protected] http://www.haskell.org/mailman/listinfo/haskell-cafe
