[Python-Dev] futures API

[Steven D'Aprano]

Brian Quinlan wrote:
> 
> On Dec 11, 2010, at 6:44 AM, Thomas Nagy wrote:

>> I have also observed a minor performance degradation with the executor 
>> replacement (3 seconds for 5000 work items). The amount of work items 
>> processed by unit of time does not seem to be a straight line: 
>> http://www.freehackers.org/~tnagy/runtime_futures_2.png .
> 
> That looks pretty linear to me.

Close to, but not quite. The graph seems to be slightly curved, with the 
amount of work done per second decreasing for large amounts of work. 
Assuming that this performance degradation is real, and not an artifact 
of the measurement technique, it seems to be quite small. I'd be happy 
to describe it as "linear" in the same way we describe dictionary 
lookups as constant-time, even though technically that's not strictly 
true. (They're linear in the number of items with a matching hash, and 
there are probably other complications as well.)

As drawn, the curve seems to fall away like a log graph, which might 
suggest to the casual viewer that this is a good thing. It may be better 
to reverse the axes, that is to have the independent variable, number of 
tasks, on the horizontal axis, and the dependent variable, cost (time 
taken), vertically. This will make it clear that the incremental cost of 
doing one extra task increases (slightly) as the number of tasks goes up.



-- 
Steven