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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Ada.Execution_Time
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Date: Fri, 17 Dec 2010 10:32:27 +0100
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On Fri, 17 Dec 2010 10:49:26 +0200, Niklas Holsti wrote:

> Dmitry A. Kazakov wrote:
>> CPU_Time has no physical meaning. 2s might be 2.5s
>> real time or 1 year real time.
> 
> CPU_Time values have physical meaning after being summed over all tasks. 
> The sum should be the real time, as closely as possible.

1. Not tasks, but threads + kernel services + kernel drivers + CPU
frequency slowdowns => a) wrong; b) out of Ada scope => cannot be mandated

2. Not so anyway under many OSes => again, cannot be mandated

3. The intended purpose of CPU_Time has nothing to do with this constraint.
Nobody is interested in knowing if the actual sum is close or not to the
real time duration. It is a simulation time, which *could* be projected to
the real time in order to estimate potential CPU load. And the result
depends on the premises made.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de