Running Phobos unit tests in threads: I have data

[Atila Neves via Digitalmars-d]

On Sunday, 4 May 2014 at 17:01:23 UTC, safety0ff wrote:
> On Saturday, 3 May 2014 at 22:46:03 UTC, Andrei Alexandrescu 
> wrote:
>> On 5/3/14, 2:42 PM, Atila Neves wrote:
>>> gdc gave _very_ different results. I had to use different 
>>> modules
>>> because at some point tests started failing, but with gdc the 
>>> threaded
>>> version runs ~3x faster.
>>>
>>> On my own unit-threaded benchmarks, running the UTs for 
>>> Cerealed over
>>> and over again was only slightly slower with threads than 
>>> without. With
>>> dmd the threaded version was nearly 3x slower.
>>
>> Sounds like a severe bug in dmd or dependents. -- Andrei
>
> This reminds me of when I was parallelizing a project euler 
> solution: atomic access was so much slower on DMD that it made 
> performance worse than the single threaded version for one 
> stage of the program.
>
> I know that std.parallelism does make use of core.atomic under 
> the hood, so this may be a factor when using DMD.

Funny you should say that, a friend of mine tried porting a 
lock-free algorithm of his from Java to D a few weeks ago. The D 
version ran 3 orders of magnitude slower. Then I tried gdc and 
ldc on his code. ldc produced code running at around 80% of the 
speed of the Java version, fdc was around 30%. But dmd...