From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Why did ID choose DJGPP for Quake?
Date: Sun, 9 Jan 2000 09:30:59 +0200
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On Thu, 6 Jan 2000, Stephen Howe wrote:

> >Not quite true.  Calling real-mode services has different overheads,
> >depending what environments and waht methods are used to call
> >real-mode code from a protected-mode program.  Part of this overhead
> >is in the library (copying data to conventional memory, preparing the
> >real-mode call structures, etc.).
> 
> Ok, you are talking about the setup of parameters for a call of DPMI
> 301h/302h etc. Hrrrmmm, hardly seems much of a test as I would expect the
> majority of the time would be in the real mode function or interrupt.

If the majority of the time would be in the real-mode function, we
wouldn't be talking about the overhead of the mode switch, would we?

In reality, there *is* some overhead involved (the DJGPP FAQ spends
some time discussing the related issues in section 14.4).  How
significant it is, depends not only on the quality of the library
code, but also on the run-time environment parameters, such as what
ring does the program and/or the DPMI host run, etc.