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From: Robert Dewar <robert_dewar@my-deja.com>
Subject: Re: huge executable??
Date: 2000/05/16
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In article <87wvkvj71c.fsf@deneb.cygnus.argh.org>,
  Florian Weimer <fw-usenet@deneb.cygnus.argh.org> wrote:

> If you run multiple Ada programs (or multiple instances of the
> same program) in parallel, shared libraries can decrease cache
> pressure

Again, this is a theoretical point that probably does not
register in practice. Why? Three reasons:

1. It is only relevant at task switch times, which happen with
very course granularity compared to cache usage and access.

2. In modern operating systems (those with 20,000,000 lines of
code doing something or other :-) the task switching code itself
will often swamp the cache anyway.

3. Task switching is so slow in these same large operating
systems that it gets long with respect to the time to completely
reload the cache.

The only time you might notice this effect is if you have a
really HUGE secondary cache, and lots of little Ada programs
switching furiously, all using the runtime library furiously.

I would be *VERY* surprised if you can even rig up a test that
would show this effect in practice.

Yes, in a light real time system, inter-task cache effects can
be significant, but I just don't think you will find this is
the case in most big operating systems.


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