[Haskell-cafe] Threading and Mullticore Computation

[Andrew Coppin]

Brandon S. Allbery KF8NH wrote:
> On 2009 Mar 3, at 12:54, mwinter at brocku.ca wrote:
>> I am using GHC 6.8.3. The -O2 option made both runs faster but the 2 
>> core run
>> is still much slower that the 1 core version. Will switching to 6.10 
>> make the difference?
>
>
> If GC contention is the issue, it should.

I just tried it with GHC 6.10.1. Two capabilities is still slower. (See 
attachments. Compiled with -O2 -threaded.)

In both cases, GC time is miniscule.


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 [("GHC RTS", "Yes")
 ,("GHC version", "6.10.1")
 ,("RTS way", "rts_thr")
 ,("Host platform", "i386-unknown-mingw32")
 ,("Build platform", "i386-unknown-mingw32")
 ,("Target platform", "i386-unknown-mingw32")
 ,("Compiler unregisterised", "NO")
 ,("Tables next to code", "YES")
 ]
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Cores1 +RTS -N1 -s 
      16,918,324 bytes allocated in the heap
       1,055,836 bytes copied during GC
       1,005,356 bytes maximum residency (1 sample(s))
          29,760 bytes maximum slop
            1260 MB total memory in use (112 MB lost due to fragmentation)

  Generation 0:    32 collections,     0 parallel,  0.03s,  0.03s elapsed
  Generation 1:     1 collections,     0 parallel,  0.00s,  0.00s elapsed

  Task  0 (worker) :  MUT time:   2.53s  (  5.11s elapsed)
                      GC  time:   0.02s  (  0.02s elapsed)

  Task  1 (worker) :  MUT time:   0.00s  (  5.11s elapsed)
                      GC  time:   0.00s  (  0.00s elapsed)

  Task  2 (worker) :  MUT time:   2.30s  (  5.11s elapsed)
                      GC  time:   0.02s  (  0.02s elapsed)

  INIT  time    0.02s  (  0.00s elapsed)
  MUT   time    4.83s  (  5.11s elapsed)
  GC    time    0.03s  (  0.03s elapsed)
  EXIT  time    0.00s  (  0.00s elapsed)
  Total time    4.88s  (  5.14s elapsed)

  %GC time       0.6%  (0.6% elapsed)

  Alloc rate    3,492,815 bytes per MUT second

  Productivity  99.0% of total user, 93.9% of total elapsed

recordMutableGen_sync: 0
gc_alloc_block_sync: 0
whitehole_spin: 0
gen[0].steps[0].sync_todo: 0
gen[0].steps[0].sync_large_objects: 0
gen[0].steps[1].sync_todo: 0
gen[0].steps[1].sync_large_objects: 0
gen[1].steps[0].sync_todo: 0
gen[1].steps[0].sync_large_objects: 0
-------------- next part --------------
Cores1 +RTS -N2 -s 
      16,926,532 bytes allocated in the heap
       1,243,560 bytes copied during GC
         794,980 bytes maximum residency (2 sample(s))
          12,012 bytes maximum slop
            1927 MB total memory in use (160 MB lost due to fragmentation)

  Generation 0:    23 collections,     8 parallel,  0.00s,  0.00s elapsed
  Generation 1:     2 collections,     0 parallel,  0.02s,  0.02s elapsed

  Parallel GC work balance: 1.00 (1267 / 1267, ideal 2)

  Task  0 (worker) :  MUT time:   0.00s  (  0.00s elapsed)
                      GC  time:   0.00s  (  0.00s elapsed)

  Task  1 (worker) :  MUT time:   3.63s  (  4.67s elapsed)
                      GC  time:   0.00s  (  0.00s elapsed)

  Task  2 (worker) :  MUT time:   0.00s  (  4.67s elapsed)
                      GC  time:   0.00s  (  0.00s elapsed)

  Task  3 (worker) :  MUT time:   3.42s  (  4.67s elapsed)
                      GC  time:   0.02s  (  0.02s elapsed)

  Task  4 (worker) :  MUT time:   0.00s  (  4.67s elapsed)
                      GC  time:   0.00s  (  0.00s elapsed)

  INIT  time    0.02s  (  0.00s elapsed)
  MUT   time    7.05s  (  4.67s elapsed)
  GC    time    0.02s  (  0.02s elapsed)
  EXIT  time    0.00s  (  0.00s elapsed)
  Total time    7.08s  (  4.69s elapsed)

  %GC time       0.2%  (0.3% elapsed)

  Alloc rate    2,396,677 bytes per MUT second

  Productivity  99.6% of total user, 150.3% of total elapsed

recordMutableGen_sync: 0
gc_alloc_block_sync: 0
whitehole_spin: 0
gen[0].steps[0].sync_todo: 0
gen[0].steps[0].sync_large_objects: 0
gen[0].steps[1].sync_todo: 0
gen[0].steps[1].sync_large_objects: 0
gen[1].steps[0].sync_todo: 0
gen[1].steps[0].sync_large_objects: 0