Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Tue, 6 Nov 2001 03:08:36 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Tue, 6 Nov 2001 03:08:16 -0500 Received: from mail009.syd.optusnet.com.au ([203.2.75.170]:689 "EHLO mail009.syd.optusnet.com.au") by vger.kernel.org with ESMTP id ; Tue, 6 Nov 2001 03:08:10 -0500 Date: Tue, 6 Nov 2001 19:07:57 +1100 To: linux-kernel@vger.kernel.org Cc: riel@conectiva.com.br Subject: Re: Scheduling of low-priority background processes Message-ID: <20011106190757.A28090@beernut.flames.org.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: From: Kevin Easton Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > > 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 ;) > What if the SCHED_IDLE behaviour only applies when the process is in userspace? Couldn't scheduler compare the process's instruction pointer against the kernel/user break point, and if the process is in the kernel, then just treat it like a normal process? > > regards, > > > Rik - 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/