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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: basic question on Ada tasks and running on different cores
Date: Thu, 17 May 2012 23:12:22 -0500
Organization: Jacob Sparre Andersen Research & Innovation
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Date: 2012-05-17T23:12:22-05:00
List-Id: <comp.lang.ada>

"Jeffrey Carter" <spam.jrcarter.not@spam.not.acm.org> wrote in message 
news:jp1ivb$o6m$1@adenine.netfront.net...
> On 05/16/2012 05:11 PM, Randy Brukardt wrote:
>>
>> The problem is, if you're trying to implement fine-grained parallelism, 
>> you
>> have to surround that code with some sort of scheduling mechanism, and 
>> that
>> overhead means you aren't going to get anywhere near 100% of the CPU at 
>> any
>> point.
>
> The assumption here is that there are more tasks/threads/parallel things 
> than there are processors/cores. That's generally true now, but they way 
> things are going, it may not be true in the not-too-distant future (1-atom 
> transistors could make for a lot of cores). When you have a core per task 
> you no longer need scheduling.

Scheduling includes deciding *what* to run, as well as *when* to run it. If 
there are enough cores, *when* becomes trivial, but *what* still requires 
overhead (and data communication, as Dmitry noted). There are special cases 
were *what* is pre-determined (SIMD machines), but for general workloads, 
determining what to run will still add costs.

                                           Randy.