Luca's meaningless thoughts  

Stats for the basic GC

by Leandro Lucarella on 2009- 10- 08 20:08 (updated on 2009- 10- 08 20:08)
tagged basic, benchmark, d, dgc, dgcbench, en, gc, statistics - with 0 comment(s)

Here are some graphs made from my D GC benchmarks using the Tango (0.99.8) basic collector, similar to the naive ones but using histograms for allocations (time and space):

big_arrays rnd_data rnd_data_2 split tree

Some comments:

  • The Wasted space is the Uncommitted space (since the basic GC doesn't track the real size of the stored object).
  • The Stop-the-world time is the time all the threads are stopped, which is almost the same as the time spent scanning the heap.
  • The Collect time is the total time spent in a collection. The difference with the Stop-the-world time is almost the same as the time spent in the sweep phase, which is done after the threads have being resumed (except the thread that triggered the collection).

There are a few observations to do about the results:

  • The stop the world time varies a lot. There are tests where is almost unnoticeable (tree), tests where it's almost equals to the total collection time (rnd_data, rnd_data_2, split) and test where it's in the middle (big_arrays). I can't see a pattern though (like heap occupancy).
  • There are tests where it seems that collections are triggered for no reason; there is plenty of free space when it's triggered (tree and big_arrays). I haven't investigated this yet, so if you can see a reason, please let me know.