[GHC] #9067: Optimize clearNursery by short-circuiting when we get to currentNursery
#9067: Optimize clearNursery by short-circuiting when we get to currentNursery ------------------------------+-------------------------------------------- Reporter: ezyang | Owner: ezyang Type: task | Status: new Priority: low | Milestone: Component: Runtime | Version: 7.9 System | Operating System: Unknown/Multiple Keywords: | Type of failure: Runtime performance bug Architecture: | Test Case: Unknown/Multiple | Blocking: Difficulty: Unknown | Blocked By: | Related Tickets: | ------------------------------+-------------------------------------------- This is a note to myself so I don't forget about this. Essentially, we can do something like this (this particular patch variant untested): {{{ diff --git a/rts/sm/Storage.c b/rts/sm/Storage.c index 36776b9..0311042 100644 --- a/rts/sm/Storage.c +++ b/rts/sm/Storage.c @@ -598,6 +598,11 @@ clearNursery (Capability *cap) ASSERT(bd->gen_no == 0); ASSERT(bd->gen == g0); IF_DEBUG(sanity,memset(bd->start, 0xaa, BLOCK_SIZE)); + if (bd == cap->r.rCurrentNursery) { + IF_DEBUG(sanity, for (bd = bd->link; bd; bd = bd->link) + ASSERT(bd->free == bd->start)); + break; + } } } } }}} This is due to invariants about how we manage the currentNursery pointer. But we need a note about it, and I need to test it more carefully. This optimization probably doesn't help too much on normal GHC, but when I have lots of nurseries it helps quite a bit. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9067 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#9067: Optimize clearNursery by short-circuiting when we get to currentNursery --------------------------------------------+------------------------------ Reporter: ezyang | Owner: ezyang Type: task | Status: new Priority: low | Milestone: Component: Runtime System | Version: 7.9 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime performance bug | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: --------------------------------------------+------------------------------ Comment (by simonmar): Andreas Voellmy and I talked about some similar ideas. I doubt that you want to rely on `CurrentNursery`, because we want to reset that after every GC, but instead I think the right approach is to assume that every block from `CurrentNursery` onwards needs to have its free pointer reset before we use it. It's a somewhat subtle invariant and something else we have to get right, but the win seems to be worthwhile. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9067#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#9067: Optimize clearNursery by short-circuiting when we get to currentNursery -------------------------------------+------------------------------------- Reporter: ezyang | Owner: ezyang Type: task | Status: new Priority: low | Milestone: Component: Runtime | Version: 7.9 System | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: Runtime | Related Tickets: performance bug | Test Case: | Blocking: | Differential Revisions: Phab:D318 | -------------------------------------+------------------------------------- Changes (by simonmar): * differential: => Phab:D318 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9067#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#9067: Optimize clearNursery by short-circuiting when we get to currentNursery
-------------------------------------+-------------------------------------
Reporter: ezyang | Owner: ezyang
Type: task | Status: closed
Priority: low | Milestone:
Component: Runtime | Version: 7.9
System | Keywords:
Resolution: fixed | Architecture: Unknown/Multiple
Operating System: | Difficulty: Unknown
Unknown/Multiple | Blocked By:
Type of failure: Runtime | Related Tickets:
performance bug |
Test Case: |
Blocking: |
Differential Revisions: Phab:D318 |
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Changes (by ezyang):
* status: new => closed
* resolution: => fixed
Comment:
{{{
commit e22bc0dedb9e9da0176ad7ce4a74acbefedc7207
Author: Simon Marlow
#9067: Optimize clearNursery by short-circuiting when we get to currentNursery -------------------------------------+------------------------------------- Reporter: ezyang | Owner: ezyang Type: task | Status: closed Priority: low | Milestone: 7.10.1 Component: Runtime | Version: 7.9 System | Keywords: Resolution: fixed | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: Runtime | Related Tickets: performance bug | Test Case: | Blocking: | Differential Revisions: Phab:D318 | -------------------------------------+------------------------------------- Changes (by ezyang): * milestone: => 7.10.1 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9067#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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