Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site ncr-sd.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxn!ihnp4!ncr-sd!greg From: greg@ncr-sd.UUCP (Greg Noel) Newsgroups: net.unix-wizards Subject: Re: 4.2 scheduler Message-ID: <355@ncr-sd.UUCP> Date: Wed, 11-Dec-85 19:51:59 EST Article-I.D.: ncr-sd.355 Posted: Wed Dec 11 19:51:59 1985 Date-Received: Fri, 13-Dec-85 07:39:48 EST References: <1360@wanginst.UUCP> <879@psivax.UUCP> <3043@sun.uucp> <882@psivax.UUCP> <3058@sun.uucp> <893@psivax.UUCP> Reply-To: greg@ncr-sd.UUCP (Greg Noel) Organization: NCR Corporation, San Diego Lines: 24 In article <893@psivax.UUCP> friesen@psivax.UUCP (Stanley Friesen) writes: > I don't really know, but I suspect that specialized, >tailor-made support code is going to be more efficient than the >generalized support available from the kernel. Er, no. There are two reasons why not. First, "tailor-made" support code is often \less/ efficient than the corresponding general-but-highly-optimized code in the kernel simply because more attention has been paid to making it efficient, and secondly, a global resource manager can often make \better/ decisions than a local, narrowly-focused one. That's why you are willing to "pay" for such services -- it may not be quite as optimal for the individual user, but it gives better system-level performance. The concept that it can be more efficient to expend cycles in the kernel seems to be a difficult one for a lot of people to comprehend. I once argued this point with Grace Hooper and could never get her to accept that anything run in kernel mode (really, anything that turned on the supervisor-state light on the 360 panel) could be anything but overhead. I suspect that this is because on an IBM-class operating system, where the user program has to carry around all the access routines and run them in user mode, most of the supervisor-state code \is/ overhead. 'Tain't so with Unix and to blindly apply the same methods to measure "efficiency" is to end up comparing apples and oranges. -- -- Greg Noel, NCR Rancho Bernardo Greg@ncr-sd.UUCP or Greg@nosc.ARPA