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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Large number of tasks slows down my program (using debian) - any
 fix?
Date: Fri, 30 Mar 2018 19:09:49 -0500
Organization: JSA Research & Innovation
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Date: 2018-03-30T19:09:49-05:00
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"Paul Rubin" <no.email@nospam.invalid> wrote in message 
news:87h8ox1ect.fsf@nightsong.com...
> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
...
>> ...  Assuming the time quant is 10ms...: 10 x 500 / 4 = 1.25s [+125ms]
>> is the time a task gets back to a core. 1.3s is an eternity.
>
> Sure, if all 500 tasks are cpu-busy then things are in a dreadful state,
> but usually the reason to use so many tasks is concurrent i/o, i.e. most
> of the threads are blocked awaiting input.

If you know what you are doing, surely. Since the OP was experimenting, who 
knows?

Assuming that you don't want to wait for your favorite compiler to implement 
Ada 2020 (probably a few years yet, we have to figure out what Ada 2020 is 
first ;-), my recommendation for parallel execution is to use Brad Moore's 
Paraffin libraries. They take care of things like load balancing and 
chunking to make good use out of your CPU resources. One can't do that just 
by launching one task per iteration for the reasons outlined above.

                      Randy.