Xref: utzoo comp.unix.wizards:11065 comp.os.misc:510
Path: utzoo!attcan!uunet!husc6!bloom-beacon!mcgill-vision!mouse
From: mouse@mcgill-vision.UUCP (der Mouse)
Newsgroups: comp.unix.wizards,comp.os.misc
Subject: Re: Reducing system calls overhead
Message-ID: <1308@mcgill-vision.UUCP>
Date: 11 Sep 88 10:45:53 GMT
References: <21606@ccicpg.UUCP> <28575@oliveb.olivetti.com>
Organization: McGill University, Montreal
Lines: 24

In article <28575@oliveb.olivetti.com>, jerry@olivey.olivetti.com (Jerry Aguirre) writes:
> In article <21606@ccicpg.UUCP> goshen@ccicpg.UUCP (Shmuel Goshen) writes:
>> The second approach would be to introduce a simple and quick
>> interface for "light weight" system calls [...].
> I once did this for a proprietary OS (not Unix).  [description of how
> this was a win in this case.]

We have a MicroVAX with an auxiliary CPU in it, something for which
very little software appears to exist.  We were building some, which
involved writing a kernel to run on the auxiliary.  In this particular
system, there was one syscall which was used very heavily, and it was a
very simple one: set a couple of flags and return (except for once in a
long while, in which case it did a good deal of work).  Well, it turned
out that adding a couple of tests to the chmk handler to test for that
particular syscall got us a factor of about 5 improvement.  Quite a
win.  (Ultimately, we got an even bigger win my making those particular
flags reside in a piece of memory which was made writeable by user
mode, so no mode-change was necessary.  Turned a full syscall, with all
its overhead, into a assign, test, plus a syscall in the "hard" case.)

					der Mouse

			old: mcgill-vision!mouse
			new: mouse@larry.mcrcim.mcgill.edu