[erlang-questions] Optimization for the ++ operator

Heinz N. Gies <>
Fri Jun 8 18:25:32 CEST 2012


The very unlikely is the important part here ;) also imagine mars position causes it to catch a astroid in it's gravitation field and slingshots it right into your computer - now that would screw your benchmark results!
--
Heinz N. Gies

http://licenser.net

On Jun 1, 2012, at 15:09, Gustav Simonsson wrote:

> On 2012-06-01 12:07, Björn-Egil Dahlberg wrote:
>> 
>> 
>> 1 jun 2012 kl. 10:46 skrev "José Valim" <>:
>> 
>>> The '++' operator does not verify that the second argument is a list.
>>> Therefore, the compiler will rewrite the first expression to simply:
>>> 
>>> [$F,$o,$o|Bar]
>>> 
>>> Yes, thanks. For some weird reason I thought Erlang restricted the right side to be a list in such cases.
>>>  
>>> Have you made sure that you run each test in a newly spawned process? 
>>> Do you run the test for long enough time?
>>> 
>>> Running in a newly spawned process did the trick, the results are now consistent.
>>> I was already running it 1000 times, here is the code (without using spawn):
>>> 
>>> https://www.refheap.com/paste/2954
>>> 
>>> I assume having a "clean" heap (reducing the chance of garbage collection) is the reason why it is a good idea to run benchmarks in a newly spawned process?
>> 
>> If you want to vary one parameter in a test, make sure all other parameters stays the same otherwise you have no idea what you are measuring!
>> 
>> Code loading, heaps, position of mars .. Everything has to be taken into account.
> 
> The effect of Mars magnetic field on that of Earth, even if Earth's aphelion and the perihelion of Mars were to coincide and the interplanetary distance were to be at its theoretical minimum, is negligible compared to the normal variations in Earth's magnetic field. 
> 
> Therefore it's very unlikely that the relative position of Mars would affect the probability of a memory bitflip occurring due to cosmic radiation and thus affecting the benchmark.
> 
> Regards,
> Gustav Simonsson
> Erlang/OTP team
> 
>> 
>> 
>>> 
>>> Thanks Björn!
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>>> 
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>> 
>> 
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