[concurrency-interest] Some interesting (confusing?) benchmark results
coyotesqrl at gmail.com
Mon Feb 11 16:10:05 EST 2013
Your threshold seems a bit small to me, but more importantly, I don't see
you forking the left branch prior to the right.compute/left.join.
On Mon, Feb 11, 2013 at 1:52 PM, <thurston at nomagicsoftware.com> wrote:
> I made some initial attempts at using ForkJoin framework for some rather
> obvious recursively parallel use-cases, namely summing the elements of an
> int and also sorting an int (randomly filled).
> The problem-sizes I used ranged from 1M - 10M.
> I really enjoy using the framework and find it relatively easy to reason
> about my programs (if not necessarily the internals of the framework).
> But I was disappointed with the results: in both cases they were slower
> than the corresponding Java serial implementation.
> I completely understand the principle of YMMV, and I wasn't expecting 2x
> speedup, but especially in the case of the sort, but I was expecting that
> ForkJoin would do at least a little better than the single-threaded
> version. I guess what I'm asking is: are these results surprising? Does
> it mean I'm doing something wrong?
> I'll give a brief description of my implementation:
> single-threaded: Arrays.sort(int)
> ForkJoin: I'm using a merge-sort, with THRESHOLD = 250 (arrived at by
> int compute()
> if int.length < THRESHOLD
> return insertionSort(int)
> left = new MergeSort(int //split in half)
> right = new MergeSort(int //other half)
> return merge(right.compute(), left.join())
> The insertionSort() and merge() methods are just standard implementations;
> there is a bit of apples to oranges comparison since Arrays.sort() uses an
> optimized quicksort, but we're still talking O(nlog(n))
> Just ran it on my laptop:
> Windows 7 64-bit
> 1.7.0_03; Java HotSpot(TM) 64-Bit Server VM 22.1-b02
> Core 2 Duo==> 2 cores 2GHz
> 2M int:
> single-threaded: ~330ms
> ForkJoin (2 workers): ~390ms
> Would appreciate any feedback and hopefully the #s are somewhat helpful
> (and please no scoffawing at my antiquated machine)
> Concurrency-interest mailing list
> Concurrency-interest at cs.**oswego.edu <Concurrency-interest at cs.oswego.edu>
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