DiffArray performance unusable for advertized purpose
(cf. this ghc-users thread)
Data.Array.Diff.DiffArray is unusably slow. Sometimes even Data.Array.Array is faster in single-threaded use, defeating the purpose. The attached code tries to demonstrate the issue, if I got the single-threadedness via $! right (default compilation ghc --make SlowDiffArray.hs gives Array, build with -DUseDiff to get DiffArray).
As I happened to have some older ghcs around, I tried those as well, and it seems the issue got worse around 6.8.3 (SlowDiffArrayA-<version>: Array; SlowDiffArrayDA-<version>: DiffArray):
$ for i in *.exe ; do echo $i; time ./$i; done
SlowDiffArrayA-61120081004.exe
9990001
real 0m0.307s
user 0m0.015s
sys 0m0.015s
SlowDiffArrayA-641.exe
9990001
real 0m0.261s
user 0m0.030s
sys 0m0.000s
SlowDiffArrayA-661.exe
9990001
real 0m0.260s
user 0m0.015s
sys 0m0.000s
SlowDiffArrayA-683.exe
9990001
real 0m0.232s
user 0m0.015s
sys 0m0.000s
SlowDiffArrayDA-61120081004.exe
9990001
real 0m12.932s
user 0m0.031s
sys 0m0.000s
SlowDiffArrayDA-641.exe
9990001
real 0m7.114s
user 0m0.015s
sys 0m0.016s
SlowDiffArrayDA-661.exe
9990001
real 0m5.774s
user 0m0.015s
sys 0m0.015s
SlowDiffArrayDA-683.exe
9990001
real 0m12.814s
user 0m0.015s
sys 0m0.000s(measured on Pentium M 760, 2GHz, Windows XP)
[the majority of the issue probably lies in the DiffArray implementation, hence component libraries, but it seems that compiler and runtime system also play a role]
Trac metadata
| Trac field | Value |
|---|---|
| Version | 6.11 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | libraries (other) |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |