Lee Spector <lspec...@hampshire.edu> writes:
> I'm also aware that the test that produced the data I give below,
> insofar as it uses pmap to do the distribution, may leave cores idle
> for a bit if some tasks take a lot longer than others, because of the
> way that pmap allocates cores to threads.
Although it doesn’t impact your benchmark, `pmap` may be further
adversely affecting the performance of your actual program. There’s a
open bug regarding `pmap` and chunked seqs:
http://dev.clojure.org/jira/browse/CLJ-862
The impact is that `pmap` with chunked seq input will spawn futures for
its function applications in flights of 32, spawning as many flights as
necessary to reach or exceed #CPUS + 2. On a 48-way system, it will
initially launch 64 futures, then spawn an additional 32 every time the
number of active unrealized futures drops below 50, leading to
significant contention for a CPU-bound application.
I hope it can be made useful in a future version of Clojure, but right
now `pmap` is more of an attractive nuisance than anything else.
-Marshall
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