RTS option -A affecting cpu-core usage?

[Daniel Trstenjak]

Hi all,

I played around with a parallel algorithm and tried to get the GC time
down by specifying the RTS option '-A'.

But if I'm specifying '-A' than also the usage of the cpu-cores seems to
change. Without '-A' I'm getting a total cpu-core usage of '4.44s',
with '-A' I'm getting only '1.67s'.

Any ideas?


Greetings,
Daniel


Without '-A':
-------------

dan at machine ~> ghc-mod-dev find showWindows +RTS -s -N4
XMonad.Util.XUtils
     980,770,296 bytes allocated in the heap
     552,122,168 bytes copied during GC
     163,683,152 bytes maximum residency (11 sample(s))
       4,369,800 bytes maximum slop
             280 MB total memory in use (0 MB lost due to fragmentation)

                                    Tot time (elapsed)  Avg pause  Max pause
  Gen  0      1690 colls,  1690 par    2.45s    0.66s     0.0004s    0.0024s
  Gen  1        11 colls,    10 par    0.98s    0.26s     0.0239s    0.1022s

  Parallel GC work balance: 18.06% (serial 0%, perfect 100%)

  TASKS: 6 (1 bound, 5 peak workers (5 total), using -N4)

  SPARKS: 1025 (0 converted, 0 overflowed, 0 dud, 0 GC'd, 1025 fizzled)

  INIT    time    0.00s  (  0.00s elapsed)
  MUT     time    0.99s  (  0.83s elapsed)
  GC      time    3.43s  (  0.93s elapsed)
  EXIT    time    0.02s  (  0.02s elapsed)
  Total   time    4.44s  (  1.78s elapsed)

  Alloc rate    995,571,064 bytes per MUT second

  Productivity  22.7% of total user, 56.5% of total elapsed

gc_alloc_block_sync: 53552
whitehole_spin: 0
gen[0].sync: 75
gen[1].sync: 23678


With '-A':
----------

dan at machine ~> ghc-mod-dev find showWindows +RTS -s -N4 -A500m
XMonad.Util.XUtils
     979,761,872 bytes allocated in the heap
      94,043,424 bytes copied during GC
     118,609,784 bytes maximum residency (2 sample(s))
       2,844,808 bytes maximum slop
            2196 MB total memory in use (0 MB lost due to fragmentati

                                    Tot time (elapsed)  Avg pause  Ma
  Gen  0         0 colls,     0 par    0.00s    0.00s     0.0000s    
  Gen  1         2 colls,     1 par    0.47s    0.18s     0.0878s    

  Parallel GC work balance: 57.02% (serial 0%, perfect 100%)

  TASKS: 6 (1 bound, 5 peak workers (5 total), using -N4)

  SPARKS: 1025 (616 converted, 0 overflowed, 0 dud, 0 GC'd, 409 fizzl

  INIT    time    0.02s  (  0.02s elapsed)
  MUT     time    1.16s  (  1.16s elapsed)
  GC      time    0.47s  (  0.18s elapsed)
  EXIT    time    0.02s  (  0.02s elapsed)
  Total   time    1.67s  (  1.38s elapsed)

  Alloc rate    844,914,346 bytes per MUT second

  Productivity  70.8% of total user, 85.9% of total elapsed

gc_alloc_block_sync: 33458
whitehole_spin: 0
gen[0].sync: 5372
gen[1].sync: 0