*BSD News Article 51051


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From: gary@first.acadia.net (Gary Robinson)
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: "An HTTP software server can pummel a CPU..."
Date: Sun, 17 Sep 1995 09:12:31 -0500
Organization: First Software, Inc.
Lines: 37
Message-ID: <gary-1709950912310001@bhb21.acadia.net>
References: <gary-1309951409030001@bhb17.acadia.net> <439ooa$fdc@bonnie.tcd-dresden.de>
NNTP-Posting-Host: bhb21.acadia.net

Joerg,

Thanks for the excellent explanation about priorities in Unix.  

Gary




In article <439ooa$fdc@bonnie.tcd-dresden.de>,
joerg_wunsch@uriah.heep.sax.de wrote:

> Gary Robinson <gary@first.acadia.net> wrote:
> 
> >[ Now that I think of it, I maybe I do remember hearing before that Unix
> >didn't allow priorities ].
> 
> Unix is considered a time-sharing o/s (as opposed to a real-time o/s)
> and as such has no static priority handling (and hence no guaranteed
> response time).  However, there is a mechanism to modify the initial
> priority of a process, called "nice" (see nice(1) and nice(3)).
> 
> Further, the basics of the scheduler are arranged so that it would
> lower the priority of processes that did consume much CPU, while it
> will raise the priority of processes that used to have long sleep
> times (i.e., were waiting for I/O to complete), in order to give them
> a better interactive response behaviour.
> 
> You can also limit the amount of CPU a process will be allowed to get
> _in total_, it will be killed after exceeding this amount (but you can
> arrange it to send the process a SIGXCPU first).  See [sg]etrlimit(2)
> and the csh-builtin command limit.
> -- 
> cheers, J"org                      private:   joerg_wunsch@uriah.heep.sax.de
>                                    http://www.sax.de/~joerg/
> 
> Never trust an operating system you don't have sources for. ;-)