1. 18 Dec, 2017 1 commit
  2. 08 Jun, 2017 1 commit
    • Simon Marlow's avatar
      Fix a lost-wakeup bug in BLACKHOLE handling (#13751) · 59847290
      Simon Marlow authored
      Summary:
      The problem occurred when
      * Threads A & B evaluate the same thunk
      * Thread A context-switches, so the thunk gets blackholed
      * Thread C enters the blackhole, creates a BLOCKING_QUEUE attached to
        the blackhole and thread A's `tso->bq` queue
      * Thread B updates the blackhole with a value, overwriting the BLOCKING_QUEUE
      * We GC, replacing A's update frame with stg_enter_checkbh
      * Throw an exception in A, which ignores the stg_enter_checkbh frame
      
      Now we have C blocked on A's tso->bq queue, but we forgot to check the
      queue because the stg_enter_checkbh frame has been thrown away by the
      exception.
      
      The solution and alternative designs are discussed in Note [upd-black-hole].
      
      This also exposed a bug in the interpreter, whereby we were sometimes
      context-switching without calling `threadPaused()`.  I've fixed this
      and added some Notes.
      
      Test Plan:
      * `cd testsuite/tests/concurrent && make slow`
      * validate
      
      Reviewers: niteria, bgamari, austin, erikd
      
      Reviewed By: erikd
      
      Subscribers: rwbarton, thomie
      
      GHC Trac Issues: #13751
      
      Differential Revision: https://phabricator.haskell.org/D3630
      59847290
  3. 29 Apr, 2017 1 commit
  4. 07 Dec, 2016 1 commit
    • Simon Marlow's avatar
      Overhaul of Compact Regions (#12455) · 7036fde9
      Simon Marlow authored
      Summary:
      This commit makes various improvements and addresses some issues with
      Compact Regions (aka Compact Normal Forms).
      
      This was the most important thing I wanted to fix.  Compaction
      previously prevented GC from running until it was complete, which
      would be a problem in a multicore setting.  Now, we compact using a
      hand-written Cmm routine that can be interrupted at any point.  When a
      GC is triggered during a sharing-enabled compaction, the GC has to
      traverse and update the hash table, so this hash table is now stored
      in the StgCompactNFData object.
      
      Previously, compaction consisted of a deepseq using the NFData class,
      followed by a traversal in C code to copy the data.  This is now done
      in a single pass with hand-written Cmm (see rts/Compact.cmm). We no
      longer use the NFData instances, instead the Cmm routine evaluates
      components directly as it compacts.
      
      The new compaction is about 50% faster than the old one with no
      sharing, and a little faster on average with sharing (the cost of the
      hash table dominates when we're doing sharing).
      
      Static objects that don't (transitively) refer to any CAFs don't need
      to be copied into the compact region.  In particular this means we
      often avoid copying Char values and small Int values, because these
      are static closures in the runtime.
      
      Each Compact# object can support a single compactAdd# operation at any
      given time, so the Data.Compact library now enforces mutual exclusion
      using an MVar stored in the Compact object.
      
      We now get exceptions rather than killing everything with a barf()
      when we encounter an object that cannot be compacted (a function, or a
      mutable object).  We now also detect pinned objects, which can't be
      compacted either.
      
      The Data.Compact API has been refactored and cleaned up.  A new
      compactSize operation returns the size (in bytes) of the compact
      object.
      
      Most of the documentation is in the Haddock docs for the compact
      library, which I've expanded and improved here.
      
      Various comments in the code have been improved, especially the main
      Note [Compact Normal Forms] in rts/sm/CNF.c.
      
      I've added a few tests, and expanded a few of the tests that were
      there.  We now also run the tests with GHCi, and in a new test way
      that enables sanity checking (+RTS -DS).
      
      There's a benchmark in libraries/compact/tests/compact_bench.hs for
      measuring compaction speed and comparing sharing vs. no sharing.
      
      The field totalDataW in StgCompactNFData was unnecessary.
      
      Test Plan:
      * new unit tests
      * validate
      * tested manually that we can compact Data.Aeson data
      
      Reviewers: gcampax, bgamari, ezyang, austin, niteria, hvr, erikd
      
      Subscribers: thomie, simonpj
      
      Differential Revision: https://phabricator.haskell.org/D2751
      
      GHC Trac Issues: #12455
      7036fde9
  5. 29 Nov, 2016 1 commit
  6. 14 Nov, 2016 1 commit
    • Simon Marlow's avatar
      Remove CONSTR_STATIC · 55d535da
      Simon Marlow authored
      Summary:
      We currently have two info tables for a constructor
      
      * XXX_con_info: the info table for a heap-resident instance of the
        constructor, It has type CONSTR, or one of the specialised types like
        CONSTR_1_0
      
      * XXX_static_info: the info table for a static instance of this
        constructor, which has type CONSTR_STATIC or CONSTR_STATIC_NOCAF.
      
      I'm getting rid of the latter, and using the `con_info` info table for
      both static and dynamic constructors.  For rationale and more details
      see Note [static constructors] in SMRep.hs.
      
      I also removed these macros: `isSTATIC()`, `ip_STATIC()`,
      `closure_STATIC()`, since they relied on the CONSTR/CONSTR_STATIC
      distinction, and anyway HEAP_ALLOCED() does the same job.
      
      Test Plan: validate
      
      Reviewers: bgamari, simonpj, austin, gcampax, hvr, niteria, erikd
      
      Subscribers: thomie
      
      Differential Revision: https://phabricator.haskell.org/D2690
      
      GHC Trac Issues: #12455
      55d535da
  7. 20 Jul, 2016 1 commit
    • gcampax's avatar
      Compact Regions · cf989ffe
      gcampax authored and Simon Marlow's avatar Simon Marlow committed
      This brings in initial support for compact regions, as described in the
      ICFP 2015 paper "Efficient Communication and Collection with Compact
      Normal Forms" (Edward Z. Yang et.al.) and implemented by Giovanni
      Campagna.
      
      Some things may change before the 8.2 release, but I (Simon M.) wanted
      to get the main patch committed so that we can iterate.
      
      What documentation there is is in the Data.Compact module in the new
      compact package.  We'll need to extend and polish the documentation
      before the release.
      
      Test Plan:
      validate
      (new test cases included)
      
      Reviewers: ezyang, simonmar, hvr, bgamari, austin
      
      Subscribers: vikraman, Yuras, RyanGlScott, qnikst, mboes, facundominguez, rrnewton, thomie, erikd
      
      Differential Revision: https://phabricator.haskell.org/D1264
      
      GHC Trac Issues: #11493
      cf989ffe
  8. 04 May, 2016 1 commit
  9. 23 Jan, 2016 1 commit
    • Joachim Breitner's avatar
      Remove unused IND_PERM · f42db157
      Joachim Breitner authored and Ben Gamari's avatar Ben Gamari committed
      it seems that this closure type has not been in use since 5d52d9, so all
      this is dead and untested code. This removes it. Some of the code might
      be useful for a counting indirection as described in #10613, so when
      implementing that, have a look at what this commit removes.
      
      Test Plan: validate on harbormaster
      
      Reviewers: austin, bgamari, simonmar
      
      Reviewed By: simonmar
      
      Subscribers: thomie
      
      Differential Revision: https://phabricator.haskell.org/D1821
      f42db157
  10. 11 Sep, 2015 1 commit
  11. 28 Jul, 2015 1 commit
    • Simon Marlow's avatar
      Eliminate zero_static_objects_list() · f83aab95
      Simon Marlow authored
      Summary:
      [Revised version of D1076 that was committed and then backed out]
      
      In a workload with a large amount of code, zero_static_objects_list()
      takes a significant amount of time, and furthermore it is in the
      single-threaded part of the GC.
      
      This patch uses a slightly fiddly scheme for marking objects on the
      static object lists, using a flag in the low 2 bits that flips between
      two states to indicate whether an object has been visited during this
      GC or not.  We also have to take into account objects that have not
      been visited yet, which might appear at any time due to runtime linking.
      
      Test Plan: validate
      
      Reviewers: austin, ezyang, rwbarton, bgamari, thomie
      
      Reviewed By: bgamari, thomie
      
      Subscribers: thomie
      
      Differential Revision: https://phabricator.haskell.org/D1106
      f83aab95
  12. 27 Jul, 2015 1 commit
  13. 22 Jul, 2015 1 commit
    • Simon Marlow's avatar
      Eliminate zero_static_objects_list() · b949c96b
      Simon Marlow authored
      Summary:
      In a workload with a large amount of code, zero_static_objects_list()
      takes a significant amount of time, and furthermore it is in the
      single-threaded part of the GC.
      
      This patch uses a slightly fiddly scheme for marking objects on the
      static object lists, using a flag in the low 2 bits that flips between
      two states to indicate whether an object has been visited during this
      GC or not.  We also have to take into account objects that have not
      been visited yet, which might appear at any time due to runtime linking.
      
      Test Plan: validate
      
      Reviewers: austin, bgamari, ezyang, rwbarton
      
      Subscribers: thomie
      
      Differential Revision: https://phabricator.haskell.org/D1076
      b949c96b
  14. 21 Oct, 2014 1 commit
  15. 29 Sep, 2014 1 commit
  16. 28 Jul, 2014 1 commit
  17. 29 Mar, 2014 1 commit
    • tibbe's avatar
      Add SmallArray# and SmallMutableArray# types · 90329b6c
      tibbe authored
      These array types are smaller than Array# and MutableArray# and are
      faster when the array size is small, as they don't have the overhead
      of a card table. Having no card table reduces the closure size with 2
      words in the typical small array case and leads to less work when
      updating or GC:ing the array.
      
      Reduces both the runtime and memory allocation by 8.8% on my insert
      benchmark for the HashMap type in the unordered-containers package,
      which makes use of lots of small arrays. With tuned GC settings
      (i.e. `+RTS -A6M`) the runtime reduction is 15%.
      
      Fixes #8923.
      90329b6c
  18. 02 Nov, 2013 1 commit
  19. 01 Oct, 2013 1 commit
  20. 19 Feb, 2013 1 commit
  21. 16 Nov, 2012 1 commit
    • Simon Marlow's avatar
      Add a write barrier for TVAR closures · 6d784c43
      Simon Marlow authored
      This improves GC performance when there are a lot of TVars in the
      heap.  For instance, a TChan with a lot of elements causes a massive
      GC drag without this patch.
      
      There's more to do - several other STM closure types don't have write
      barriers, so GC performance when there are a lot of threads blocked on
      STM isn't great.  But fixing the problem for TVar is a good start.
      6d784c43
  22. 08 Oct, 2012 1 commit
    • Simon Marlow's avatar
      Produce new-style Cmm from the Cmm parser · a7c0387d
      Simon Marlow authored
      The main change here is that the Cmm parser now allows high-level cmm
      code with argument-passing and function calls.  For example:
      
      foo ( gcptr a, bits32 b )
      {
        if (b > 0) {
           // we can make tail calls passing arguments:
           jump stg_ap_0_fast(a);
        }
      
        return (x,y);
      }
      
      More details on the new cmm syntax are in Note [Syntax of .cmm files]
      in CmmParse.y.
      
      The old syntax is still more-or-less supported for those occasional
      code fragments that really need to explicitly manipulate the stack.
      However there are a couple of differences: it is now obligatory to
      give a list of live GlobalRegs on every jump, e.g.
      
        jump %ENTRY_CODE(Sp(0)) [R1];
      
      Again, more details in Note [Syntax of .cmm files].
      
      I have rewritten most of the .cmm files in the RTS into the new
      syntax, except for AutoApply.cmm which is generated by the genapply
      program: this file could be generated in the new syntax instead and
      would probably be better off for it, but I ran out of enthusiasm.
      
      Some other changes in this batch:
      
       - The PrimOp calling convention is gone, primops now use the ordinary
         NativeNodeCall convention.  This means that primops and "foreign
         import prim" code must be written in high-level cmm, but they can
         now take more than 10 arguments.
      
       - CmmSink now does constant-folding (should fix #7219)
      
       - .cmm files now go through the cmmPipeline, and as a result we
         generate better code in many cases.  All the object files generated
         for the RTS .cmm files are now smaller.  Performance should be
         better too, but I haven't measured it yet.
      
       - RET_DYN frames are removed from the RTS, lots of code goes away
      
       - we now have some more canned GC points to cover unboxed-tuples with
         2-4 pointers, which will reduce code size a little.
      a7c0387d
  23. 21 Sep, 2012 2 commits
  24. 25 Aug, 2012 1 commit
    • ian@well-typed.com's avatar
      More CPP macros -> inline functions · 0ab537c5
      ian@well-typed.com authored
      All the wibble seem to have cancelled out, and (non-debug) object sizes
      are back to where they started.
      
      I'm not 100% sure that the types are optimal, but at least now the
      functions have types and we can fix them if necessary.
      0ab537c5
  25. 06 May, 2012 1 commit
  26. 11 Apr, 2011 1 commit
    • Simon Marlow's avatar
      Refactoring and tidy up · 1fb38442
      Simon Marlow authored
      This is a port of some of the changes from my private local-GC branch
      (which is still in darcs, I haven't converted it to git yet).  There
      are a couple of small functional differences in the GC stats: first,
      per-thread GC timings should now be more accurate, and secondly we now
      report average and maximum pause times. e.g. from minimax +RTS -N8 -s:
      
                                          Tot time (elapsed)  Avg pause  Max pause
        Gen  0      2755 colls,  2754 par   13.16s    0.93s     0.0003s    0.0150s
        Gen  1       769 colls,   769 par    3.71s    0.26s     0.0003s    0.0059s
      1fb38442
  27. 02 Feb, 2011 2 commits
    • Simon Marlow's avatar
      GC refactoring and cleanup · 18896fa2
      Simon Marlow authored
      Now we keep any partially-full blocks in the gc_thread[] structs after
      each GC, rather than moving them to the generation.  This should give
      us slightly better locality (though I wasn't able to measure any
      difference).
      
      Also in this patch: better sanity checking with THREADED.
      18896fa2
    • Simon Marlow's avatar
      A small GC optimisation · bef3da1e
      Simon Marlow authored
      Store the *number* of the destination generation in the Bdescr struct,
      so that in evacuate() we don't have to deref gen to get it.
      This is another improvement ported over from my GC branch.
      bef3da1e
  28. 15 Dec, 2010 1 commit
  29. 16 Dec, 2010 1 commit
  30. 15 Dec, 2010 1 commit
    • Simon Marlow's avatar
      Implement stack chunks and separate TSO/STACK objects · f30d5273
      Simon Marlow authored
      This patch makes two changes to the way stacks are managed:
      
      1. The stack is now stored in a separate object from the TSO.
      
      This means that it is easier to replace the stack object for a thread
      when the stack overflows or underflows; we don't have to leave behind
      the old TSO as an indirection any more.  Consequently, we can remove
      ThreadRelocated and deRefTSO(), which were a pain.
      
      This is obviously the right thing, but the last time I tried to do it
      it made performance worse.  This time I seem to have cracked it.
      
      2. Stacks are now represented as a chain of chunks, rather than
         a single monolithic object.
      
      The big advantage here is that individual chunks are marked clean or
      dirty according to whether they contain pointers to the young
      generation, and the GC can avoid traversing clean stack chunks during
      a young-generation collection.  This means that programs with deep
      stacks will see a big saving in GC overhead when using the default GC
      settings.
      
      A secondary advantage is that there is much less copying involved as
      the stack grows.  Programs that quickly grow a deep stack will see big
      improvements.
      
      In some ways the implementation is simpler, as nothing special needs
      to be done to reclaim stack as the stack shrinks (the GC just recovers
      the dead stack chunks).  On the other hand, we have to manage stack
      underflow between chunks, so there's a new stack frame
      (UNDERFLOW_FRAME), and we now have separate TSO and STACK objects.
      The total amount of code is probably about the same as before.
      
      There are new RTS flags:
      
         -ki<size> Sets the initial thread stack size (default 1k)  Egs: -ki4k -ki2m
         -kc<size> Sets the stack chunk size (default 32k)
         -kb<size> Sets the stack chunk buffer size (default 1k)
      
      -ki was previously called just -k, and the old name is still accepted
      for backwards compatibility.  These new options are documented.
      f30d5273
  31. 01 Apr, 2010 1 commit
    • Simon Marlow's avatar
      Remove the IND_OLDGEN and IND_OLDGEN_PERM closure types · 70a2431f
      Simon Marlow authored
      These are no longer used: once upon a time they used to have different
      layout from IND and IND_PERM respectively, but that is no longer the
      case since we changed the remembered set to be an array of addresses
      instead of a linked list of closures.
      70a2431f
  32. 29 Mar, 2010 2 commits
    • Simon Marlow's avatar
      tiny GC optimisation · 1373cd30
      Simon Marlow authored
      1373cd30
    • Simon Marlow's avatar
      New implementation of BLACKHOLEs · 5d52d9b6
      Simon Marlow authored
      This replaces the global blackhole_queue with a clever scheme that
      enables us to queue up blocked threads on the closure that they are
      blocked on, while still avoiding atomic instructions in the common
      case.
      
      Advantages:
      
       - gets rid of a locked global data structure and some tricky GC code
         (replacing it with some per-thread data structures and different
         tricky GC code :)
      
       - wakeups are more prompt: parallel/concurrent performance should
         benefit.  I haven't seen anything dramatic in the parallel
         benchmarks so far, but a couple of threading benchmarks do improve
         a bit.
      
       - waking up a thread blocked on a blackhole is now O(1) (e.g. if
         it is the target of throwTo).
      
       - less sharing and better separation of Capabilities: communication
         is done with messages, the data structures are strictly owned by a
         Capability and cannot be modified except by sending messages.
      
       - this change will utlimately enable us to do more intelligent
         scheduling when threads block on each other.  This is what started
         off the whole thing, but it isn't done yet (#3838).
      
      I'll be documenting all this on the wiki in due course.
      5d52d9b6
  33. 16 Mar, 2010 1 commit
    • Simon Marlow's avatar
      copy_tag_nolock(): fix write ordering and add a write_barrier() · 1a050f3c
      Simon Marlow authored
      Fixes a rare crash in the parallel GC.
      
      If we copy a closure non-atomically during GC, as we do for all
      immutable values, then before writing the forwarding pointer we better
      make sure that the closure itself is visible to other threads that
      might follow the forwarding pointer.  I imagine this doesn't happen
      very often, but I just found one case of it: in scavenge_stack, the
      RET_FUN case, after evacuating ret_fun->fun we then follow it and look
      up the info pointer.
      1a050f3c
  34. 11 Mar, 2010 1 commit
    • Simon Marlow's avatar
      Use message-passing to implement throwTo in the RTS · 7408b392
      Simon Marlow authored
      This replaces some complicated locking schemes with message-passing
      in the implementation of throwTo. The benefits are
      
       - previously it was impossible to guarantee that a throwTo from
         a thread running on one CPU to a thread running on another CPU
         would be noticed, and we had to rely on the GC to pick up these
         forgotten exceptions. This no longer happens.
      
       - the locking regime is simpler (though the code is about the same
         size)
      
       - threads can be unblocked from a blocked_exceptions queue without
         having to traverse the whole queue now.  It's a rare case, but
         replaces an O(n) operation with an O(1).
      
       - generally we move in the direction of sharing less between
         Capabilities (aka HECs), which will become important with other
         changes we have planned.
      
      Also in this patch I replaced several STM-specific closure types with
      a generic MUT_PRIM closure type, which allowed a lot of code in the GC
      and other places to go away, hence the line-count reduction.  The
      message-passing changes resulted in about a net zero line-count
      difference.
      7408b392
  35. 22 Feb, 2010 1 commit
  36. 04 Dec, 2009 1 commit
  37. 03 Dec, 2009 1 commit
    • Simon Marlow's avatar
      GC refactoring, remove "steps" · 214b3663
      Simon Marlow authored
      The GC had a two-level structure, G generations each of T steps.
      Steps are for aging within a generation, mostly to avoid premature
      promotion.  
      
      Measurements show that more than 2 steps is almost never worthwhile,
      and 1 step is usually worse than 2.  In theory fractional steps are
      possible, so the ideal number of steps is somewhere between 1 and 3.
      GHC's default has always been 2.
      
      We can implement 2 steps quite straightforwardly by having each block
      point to the generation to which objects in that block should be
      promoted, so blocks in the nursery point to generation 0, and blocks
      in gen 0 point to gen 1, and so on.
      
      This commit removes the explicit step structures, merging generations
      with steps, thus simplifying a lot of code.  Performance is
      unaffected.  The tunable number of steps is now gone, although it may
      be replaced in the future by a way to tune the aging in generation 0.
      214b3663