Date: Fri, 06 Aug 1999 08:55:10 -0600 From: Wes Peters <wes@softweyr.com> To: Mike Smith <mike@smith.net.au> Cc: Arun Sharma <adsharma@home.com>, freebsd-hackers@FreeBSD.ORG Subject: Re: Excessive assembly code ? Message-ID: <37AAF74E.BEB770A9@softweyr.com> References: <199908060705.AAA00655@dingo.cdrom.com>
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Mike Smith wrote:
>
> >
> > I wonder if so much assembly code is really necessary for FreeBSD. One
> > argument for minimal usage of assembly code is that it is easier to code
> > non trivial algorithms in C.
> >
> > One such example is the scheduler. Since the decision about which process
> > is going to run next is decided in assembly code, it is restricted to a
> > relatively dumb algorithm of scanning the runqs and picking one. If the
> > mechanism (i.e nuts and bolts of the context switch) is coded in assembly
> > and the policy (which process to pick next) is done in C, the code would
> > be much more maintainable, IMO.
> >
> > How do people feel about it here ?
>
> I've been studying this just recently. The "pick the next proc" code
> really should be MI and written carefully in C, yes. But if you look
> at the code surrounding it, for example, it needs some very careful
> thought.
>
> Much of the assembly code actually in use is there for performance or
> architecture-related reasons; in many cases if you were to rewrite in C
> you would just end up with a lot of asm() macros...
And the total amount we have now doesn't seem excessive. Historically,
UNIX has usually had 2-3% of the code in assembly, I doubt we're over that.
There are some things which are still *easier* to do in assembler, especially
on an architecture with port-mapped I/O.
--
"Where am I, and what am I doing in this handbasket?"
Wes Peters Softweyr LLC
http://softweyr.com/ wes@softweyr.com
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