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From: "G.B." <bauhaus@futureapps.invalid>
Newsgroups: comp.lang.ada
Subject: Re: can someone help me with this code (explanation)
Date: Fri, 26 Sep 2014 18:08:22 +0200
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Date: 2014-09-26T18:08:22+02:00
List-Id: <comp.lang.ada>

On 26.09.14 17:31, Björn Lundin wrote:
> On 2014-09-26 16:49, J-P. Rosen wrote:
>> Le 26/09/2014 16:15, Björn Lundin a écrit :
>>> http://www.sigada.org/conf/sa98/papers/mueller.pdf
>>>
>>> I did not read all of it, but the conclusion is that
>>> context switches are bad for performance.
>>> If a protected object can REPLACE a task, it
>>> will show in measurements. (and they did measure)
>>
>> That's a paper from 16 years ago. Computers as well as compilers have
>> evolved a lot, therefore I would not trust the paper for making a
>> decision nowadays...
>>
>
> Yes, I did point that out.
> But still, I have no problem believing
> that context switches still is bad for performance.

Task switches, or tasks in the first place, are,
apparently, heavy weight. That's by comparing two Ada programs,

http://benchmarksgame.alioth.debian.org/u64q/program.php?test=threadring&lang=gnat&id=2

to

http://benchmarksgame.alioth.debian.org/u64q/program.php?test=threadring&lang=gnat&id=4

and then both of them to the "different kind" of parallelism
exhibited by the leading entries. The leading entries are faster by
an orders of magnitude, even though the faster Ada program uses
just semaphores.

It might be better for Ada if at least the parallel loop initiatives
announced in Ada Letters are getting somewhere. I'm just guessing at
the effectiveness WRT async little things, though.