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From: Keean Schupke <keean.schupke@googlemail.com>
Newsgroups: comp.lang.ada
Subject: Re: Efficient Sequential Access to Arrays
Date: Mon, 30 Jul 2012 07:04:43 -0700 (PDT)
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Date: 2012-07-30T07:04:43-07:00
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On Monday, 30 July 2012 10:20:48 UTC+1, Georg Bauhaus  wrote:
> On 30.07.12 08:31, Jacob Sparre Andersen wrote:
> 
> > robin.vowel writes:
> 
> > 
> 
> >> On Monday, 16 July 2012 04:40:08 UTC+10, Keean Schupke  wrote:
> 
> > 
> 
> >>> The Monte-Carlo simulator I am working on is now performing better in
> 
> >>> Ada than in C++ using profile-guided compilation (57k simulations per
> 
> >>> second for Ada vs 56k simulations per second for C++).
> 
> >>
> 
> >> One part in 59 is not a significant difference.
> 
> > 
> 
> > That depends on the variance.  But reporting performance numbers without
> 
> > the corresponding variance/standard deviation is very bad style.
> 
> 
> 
> When I see fluctuations, and the system is otherwise idle,
> 
> I'll typically assume that there is something random going on
> 
> in the program or in its run-time support system, or that
> 
> some contemporary CPU lets its cores run at different
> 
> speed without me knowing a way to influence that (by, e.g.,
> 
> asking for a constant number of ins per sec that would not
> 
> create too much heat (that would force fewer ins per sec)).
> 
> Because otherwise, how could the sequence of instructions
> 
> create fluctuations if it is not self-modifying?
> 
> 
> 
> In this case, the inputs seem of fixed size, tailored to
> 
> the caches' sizes in particular, so I'll assume that the results
> 
> show that it is not universally true that equivalent programs
> 
> written in Ada or C-17 cannot be as fast as the other.


I agree with this. If you want more accuracy can write a kernel module to run the timed critical code without interrupts.


Cheers,
Keean.