Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Mon, 5 Nov 2001 20:03:49 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Mon, 5 Nov 2001 20:03:39 -0500 Received: from garrincha.netbank.com.br ([200.203.199.88]:23824 "HELO netbank.com.br") by vger.kernel.org with SMTP id ; Mon, 5 Nov 2001 20:03:26 -0500 Date: Mon, 5 Nov 2001 23:03:07 -0200 (BRST) From: Rik van Riel X-X-Sender: To: Thomas Koeller Cc: Subject: Re: Scheduling of low-priority background processes In-Reply-To: <01110521533900.00641@sarkovy.koeller.org> Message-ID: X-spambait: aardvark@kernelnewbies.org X-spammeplease: aardvark@nl.linux.org MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 5 Nov 2001, Thomas Koeller wrote: > On those systems, you could assign a scheduling priority lower than > the one nomally used by interactive processes to CPU-hogging, > numbercrunching tasks. These tasks would then use up any CPU time left > over by interactive processes without otherwise interfering with them. > I always found this feature very useful (think of SETI@home!). > But that idea is so obvious, and since nobody did it so far, I am > probably missing something. What is it? Priority inversion. I did a patch which does exactly what you describe, around the 2.1 timeframe. It worked fine most of the time, but occasionally the following happened: 1) a SCHED_IDLE process got hold of some kernel lock 2) a normal, low-priority process started eating CPU for a number of seconds 3) a high-priority normal process wanted the lock the SCHED_IDLE task had, but had to wait several seconds, at times up to a minute, before the SCHED_IDLE task got a chance to run and release the lock This wasn't too much of a problem on my own system, but of course this is an easily exploitable vulnerability for attackers. For me, this just means we should improve the scheduler so nice levels are stronger ... say that a nice +20 process only gets 1% of the CPU of a normal priority process ;) regards, Rik -- DMCA, SSSCA, W3C? Who cares? http://thefreeworld.net/ http://www.surriel.com/ http://distro.conectiva.com/ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/