February 2013 - ghc-devs

nofib comparisons between 7.0.4, 7.4.2, 7.6.1, and 7.6.2
by Johan Tibell 07 Feb '13

07 Feb '13

Hi all, I haven't had much time to do performance tzar work yet, but I did run nofib on the last few GHC releases to see the current trend. The benchmarks where run on my 64-bit Core i7-3770 @ 3.40GHz Linux machine. Here are the results: 7.0.4 to 7.4.2: ------------------------------------------------------------ -------------------- Program Size Allocs Runtime Elapsed TotalMem -------------------------------------------------------------------------------- Min -1.6% -57.3% -39.1% -36.4% -25.0% Max +21.5% +121.5% +24.5% +25.4% +300.0% Geometric Mean +8.5% -0.7% -7.1% -5.2% +2.0% The big loser here in terms of runtime is "kahan", which I added to test tight loops involving unboxed arrays and floating point arithmetic. I believe there was a regression in fromIntegral RULES during this release, which meant that some conversions between fixed-width types went via Integer, causing unnecessary allocation. 7.4.2 to 7.6.1: -------------------------------------------------------------------------------- Program Size Allocs Runtime Elapsed TotalMem -------------------------------------------------------------------------------- Min -5.1% -23.8% -11.8% -12.9% -50.0% Max +5.3% +225.5% +7.2% +8.8% +200.0% Geometric Mean -0.4% +2.1% +0.3% +0.2% +0.7% The biggest loser here in terms of runtime is "integrate". I haven't looked into why yet. 7.6.1 to 7.6.2: -------------------------------------------------------------------------------- Program Size Allocs Runtime Elapsed TotalMem -------------------------------------------------------------------------------- Min -2.9% +0.0% -4.8% -4.4% -1.9% Max +0.0% +1.0% +4.5% +6.4% +20.8% Geometric Mean -1.7% +0.0% +0.1% +0.3% +0.2% I have two takeaways: * It's worthwhile running nofib before releases as it does find some programs that regressed. * There are some other regressions out there (i.e. in code on Hackage) that aren't reflected here, suggesting that we need to add more programs to nofib. Cheers, Johan

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Stable pointers and hash table performance
by Eyal Lotem 07 Feb '13

07 Feb '13

Hey, Background ---------------- I built a hash table in C: https://github.com/Peaker/small_hash According to a few simple benchmarks (mainly, 10 million insertions), my C hash table is much faster than any Haskell data structure I tried (e.g: 8 times faster than IntMap). You can run the C benchmark (in small_hash) via: "make && ./benchmark 10000000". The other benchmarks are at: https://github.com/Peaker/hashtable_benchmarks Benchmarks results on my hardware: http://hpaste.org/81902 I was hoping to get that fast mapping goodness to Haskell, by building an FFI to it: https://github.com/Peaker/small_hash_hs In order to do FFI bindings to a C data structure, that can contain arbitrary Haskell values, I must create a lot of StablePtrs (for each Haskell value stored in the C hash table). Problem 1: ------------- Disappointingly, the FFI bindings were dozens of times slower(!) than the C code. When using +RTS -H200M the speed is about 10 times slower(!) than the C code. oprofile shows that the culprit is the Stable Ptr code. Digging in, I found that stable ptrs and stable names shared a table, despite having quite different characteristics: * Stable Names aren't considered roots by GC, ptrs are. * Making two stable ptrs for the same Haskell value doesn't really require them to unify -- so there's no need for the hash table or the "refs" counter for stable ptrs. My Changes: ----------------- I split the Stable Names into their own table (which allowed removing the "refs" field from them). Stable Ptrs no longer use a hash table to unify, don't need "refs", or "sn_obj", or "old". This made Stable Ptrs cost just 1 C ptr in the table and really cheap to create/destroy. The commits are here: https://github.com/Peaker/ghc/commits/master They are not polished (I didn't thoroughly review myself yet, didn't run the test suite, fix out-of-date comments involved) and not ready for integration yet. Result: --------- The hash table benchmark via the FFI is now only ~2 times slower than the C data structure and much faster than any other mapping structure for that particular benchmark (10 million insertions of identity integers, sequentially). A lot of the cost here is due to fine-grained allocation, as the C code does bulk allocation. I shall improve this benchmark later, and I believe it will tighten the gap some more. Problem 2: -------------- http://hackage.haskell.org/trac/ghc/ticket/7670 Every minor GC iterates a whole lot of stable ptrs. This means that with the default heap size, runtime is about 8 times longer (than with a 200M heap size). To avoid this, I'd like to split the stable ptrs table into generations. To do this, I need to know which of the pointed objects were promoted and to what generation, so I can promote my stable ptrs accordingly. It seems like the correct time to do this is in the updateStablePtrTable (now named "updateStableTables") This is the part I need help with. How do I know if an object was promoted to a higher generation when I traverse the objects? Thanks! Eyal

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simd branch ready for review
by Geoffrey Mainland 06 Feb '13

06 Feb '13

Hi Simon, I've pushed my simd branch to darcs.haskell.org. Everything has been rebased against HEAD. Simon PJ and I looked over the changes together already, but I wanted to give you (and everyone on ghc-devs) the opportunity to look things over before I merge to HEAD. Simon PJ and I came up with a few questions/notes for you, but hopefully nothing that should delay a merge. * Win32 issues Modern 32-bit x86 *NIX systems align the stack to 16-bytes, but Win32 aligns only to 4-bytes. LLVM does not assume 16-byte stack alignment. Instead, on platforms where 16-byte stack alignment is not guaranteed, it 1) always outputs a function prologue that 2) aligns the stack to a 16-byte boundary with an "and" instructions, and it also 3) disables tail calls. Because LLVM aligns the stack for a function that has SSE register spills, it also generates movaps instructions (aligned SSE moves) for the spills. This makes SSE support on Win32 difficult, and in my opinion not worth worrying about. The alternative is to 1) patch LLVM to disable the stack-alignment code so that we recover the ability to use tail calls and so that ebp scribbled over by the prologue and 2) patch the mangler to rewrite LLVM's movaps (move aligned) instructions to movups (move unaligned) instructions. I have these patches, but they are not included in the simd branch. * How hard would it be to dump ArgRep for PrimRep? It looks straightforward. Is it worth doing? * How hard would it be to track bit width in PrimRep? I recall chatting with you once about adding explicit support for, e.g., 8- and 16-bit Word/Int primops instead of relying on narrowing. Since SIMD vectors need to know the exact bit-width of their elements, I've had to create a PrimElemRep data type in compiler/types/TyCon.lhs, but I'd really like to be able to re-use PrimRep instead. * If we replaced all old-style C-- code, could we get rid of the explicit STG registers completely? Simon PJ suggested that we use real machine registers directly, so, for example, GlobalReg's constructors would have FastString fields instead of Int fields. * Could we add a CmmType field to GlobalReg's constructors? You'll see that I added a new XmmReg constructor to GlobalReg, but because I don't know the type of an XmmReg, I have to bitcast everywhere in the generated LLVM code because LLVM wants to know not just that a value is a 16-byte vector, but that it is, e.g., a 16-byte vector containing 2 64-bit doubles. Having a CmmType attached to a GlobalReg---or pairing a GlobalReg with a CmmType when assigning registers---would let me avoid all these casts. Thanks! Geoff

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Re: [commit: ghc] master: Rewrote vectorisation avoidance (based on the HS paper) (b77da25)
by David Terei 05 Feb '13

05 Feb '13

Hi Manuel, I recently committed a patch to document the -fvectorise and -favoid-vect flags. Would you mind taking a look at the documentation for these flags to ensure they are valid still with these recent changes? docs/userguide/using.xml is the file in question. Cheers, David On 5 February 2013 19:16, Manuel Chakravarty <chak(a)cse.unsw.edu.au> wrote: > Repository : ssh://darcs.haskell.org//srv/darcs/ghc > > On branch : master > > http://hackage.haskell.org/trac/ghc/changeset/b77da25ef0d95e776a43779bbb484… > >>--------------------------------------------------------------- > > commit b77da25ef0d95e776a43779bbb4843eb01d33552 > Author: Manuel M T Chakravarty <chak(a)cse.unsw.edu.au> > Date: Wed Dec 5 15:28:19 2012 +1100 > > Rewrote vectorisation avoidance (based on the HS paper) > > * Vectorisation avoidance is now the default > * Types and values from unvectorised modules are permitted in scalar code > * Simplified the VECTORISE pragmas (see http://hackage.haskell.org/trac/ghc/wiki/DataParallel/VectPragma for the spec) > * Vectorisation information is now included in the annotated Core AST > > compiler/coreSyn/CoreFVs.lhs | 11 +- > compiler/coreSyn/CoreSubst.lhs | 11 +- > compiler/coreSyn/CoreSyn.lhs | 4 +- > compiler/coreSyn/PprCore.lhs | 3 +- > compiler/deSugar/Desugar.lhs | 2 +- > compiler/hsSyn/HsDecls.lhs | 10 +- > compiler/iface/LoadIface.lhs | 14 +- > compiler/iface/MkIface.lhs | 18 +- > compiler/iface/TcIface.lhs | 30 +- > compiler/main/HscTypes.lhs | 54 +- > compiler/main/TidyPgm.lhs | 10 +- > compiler/parser/Parser.y.pp | 5 +- > compiler/rename/RnSource.lhs | 10 +- > compiler/typecheck/TcBinds.lhs | 9 +- > compiler/typecheck/TcHsSyn.lhs | 2 +- > compiler/vectorise/Vectorise.hs | 394 ++++------ > compiler/vectorise/Vectorise/Convert.hs | 18 +- > compiler/vectorise/Vectorise/Env.hs | 86 +-- > compiler/vectorise/Vectorise/Exp.hs | 1026 +++++++++++++------------ > compiler/vectorise/Vectorise/Monad.hs | 26 +- > compiler/vectorise/Vectorise/Monad/Global.hs | 60 +- > compiler/vectorise/Vectorise/Monad/InstEnv.hs | 13 +- > compiler/vectorise/Vectorise/Monad/Local.hs | 22 +- > compiler/vectorise/Vectorise/Type/Classify.hs | 42 +- > compiler/vectorise/Vectorise/Type/Env.hs | 211 +++--- > compiler/vectorise/Vectorise/Type/Type.hs | 13 +- > compiler/vectorise/Vectorise/Utils.hs | 25 +- > 27 files changed, 1066 insertions(+), 1063 deletions(-) > > > Diff suppressed because of size. To see it, use: > > git show b77da25ef0d95e776a43779bbb4843eb01d33552 > > _______________________________________________ > ghc-commits mailing list > ghc-commits(a)haskell.org > http://www.haskell.org/mailman/listinfo/ghc-commits

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Re: [commit: nofib] master: Note why all shootout benchmarks couldn't be added (c82455f)
by Ian Lynagh 05 Feb '13

05 Feb '13

Hi Johan, On Tue, Feb 05, 2013 at 03:19:59PM -0800, Johan Tibell wrote: > > + * The k-nucleotide benchmark wasn't included as it segfaults on my > + 64-bit OS X 10.8.2 machine. That sounds more serious than a performance regression! Or is it a bug in the benchmark? Thanks Ian

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Re: [commit: ghc] master: Add the new random commit again (6a46b46)
by Gabor Greif 05 Feb '13

05 Feb '13

Hi Ian, since you have pinned a commit that is on a branch, people whose clones do not track that branch will never see the commit: $ ( cd libraries/random ; git remote show; git remote show origin ) origin * remote origin Fetch URL: https://github.com/ghc/packages-random.git Push URL: https://github.com/ghc/packages-random.git HEAD branch: master Remote branch: master tracked Local ref configured for 'git push': master pushes to master (up to date) This may be the problem what we see. Possibly the 'sync-all' script could be amended, so that your 'ghc-head' branch is added to the remote? Cheers, Gabor On 2/5/13, Ian Lynagh <igloo(a)earth.li> wrote: > Repository : ssh://darcs.haskell.org//srv/darcs/ghc > > On branch : master > > http://hackage.haskell.org/trac/ghc/changeset/6a46b4627d4f3f81d65bf6b5b5c0b… > >>--------------------------------------------------------------- > > commit 6a46b4627d4f3f81d65bf6b5b5c0bcf86607c463 > Author: Ian Lynagh <ian(a)well-typed.com> > Date: Tue Feb 5 14:08:05 2013 +0000 > > Add the new random commit again > >>--------------------------------------------------------------- > > libraries/random | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/libraries/random b/libraries/random > index 69bfde2..2117e38 160000 > --- a/libraries/random > +++ b/libraries/random > @@ -1 +1 @@ > -Subproject commit 69bfde219bab869729fdbe9c1496371f912bf41e > +Subproject commit 2117e38729adaa4f465f3c5b7a8c5c4d77702d3f > > > > _______________________________________________ > ghc-commits mailing list > ghc-commits(a)haskell.org > http://www.haskell.org/mailman/listinfo/ghc-commits >

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Git confusion
by Ian Lynagh 04 Feb '13

04 Feb '13

Hi all, If I do git clone darcs.haskell.org:/srv/darcs/ghc.git cd ghc git show origin then the output is [...] Local branch configured for 'git pull': master merges with remote master [...] However, none of: git remote rm origin git remote add origin darcs.haskell.org:/srv/darcs/ghc.git git remote show origin git remote rm origin git remote add origin darcs.haskell.org:/srv/darcs/ghc.git -m master git remote show origin git remote rm origin git remote add origin darcs.haskell.org:/srv/darcs/ghc.git -t master git remote show origin git remote rm origin git remote add origin darcs.haskell.org:/srv/darcs/ghc.git -t master -m master git remote show origin have the "Local branch configured for 'git pull':" section. So having done "git remote rm origin", how do I configure the git pull branches again? Thanks Ian

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links to diffs on ghc-commit emails seem to be broken
by Carter Schonwald 04 Feb '13

04 Feb '13

Hey all, links seem to not work, though they are included in the emails eg from the email [commit: ghc] master: Move AsmCodeGen.makeFarBranches to PPC.Instr (#709) (aa1d7d3) http://hackage.haskell.org/trac/ghc/changeset/aa1d7d35ac27625c9aa67fe71c186… *should* these be broken or is something needing to be fixed up? thanks -Carter

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Re: [commit: ghc] master: Follow random submodule change (ca5d15a)
by Manuel M T Chakravarty 04 Feb '13

04 Feb '13

Ian, That still doesn't work: > Cloning into 'libraries/random'... > fatal: reference is not a tree: 2117e38729adaa4f465f3c5b7a8c5c4d77702d3f > Unable to checkout '2117e38729adaa4f465f3c5b7a8c5c4d77702d3f' in submodule path 'libraries/random' Also: http://darcs.haskell.org/ghcBuilder/builders/tn23/826/3.html Manuel Ian Lynagh <igloo(a)earth.li>: > Repository : ssh://darcs.haskell.org//srv/darcs/ghc > > On branch : master > > http://hackage.haskell.org/trac/ghc/changeset/ca5d15a61c45d6ea763872df46efe… > >> --------------------------------------------------------------- > > commit ca5d15a61c45d6ea763872df46efe5c7b33f8186 > Author: Ian Lynagh <igloo(a)earth.li> > Date: Sun Feb 3 16:29:17 2013 +0000 > > Follow random submodule change > >> --------------------------------------------------------------- > > libraries/random | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/libraries/random b/libraries/random > index 69bfde2..2117e38 160000 > --- a/libraries/random > +++ b/libraries/random > @@ -1 +1 @@ > -Subproject commit 69bfde219bab869729fdbe9c1496371f912bf41e > +Subproject commit 2117e38729adaa4f465f3c5b7a8c5c4d77702d3f > > > > _______________________________________________ > ghc-commits mailing list > ghc-commits(a)haskell.org > http://www.haskell.org/mailman/listinfo/ghc-commits

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