From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261216AbVA1JDK (ORCPT ); Fri, 28 Jan 2005 04:03:10 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261223AbVA1JDK (ORCPT ); Fri, 28 Jan 2005 04:03:10 -0500 Received: from mail.joq.us ([67.65.12.105]:58339 "EHLO sulphur.joq.us") by vger.kernel.org with ESMTP id S261216AbVA1JDD (ORCPT ); Fri, 28 Jan 2005 04:03:03 -0500 To: Ingo Molnar Cc: Nick Piggin , Paul Davis , Con Kolivas , linux , rlrevell@joe-job.com, CK Kernel , utz , Andrew Morton , alexn@dsv.su.se, Rui Nuno Capela , Chris Wright , Arjan van de Ven Subject: Re: [patch, 2.6.11-rc2] sched: RLIMIT_RT_CPU_RATIO feature References: <87hdl940ph.fsf@sulphur.joq.us> <20050124085902.GA8059@elte.hu> <20050124125814.GA31471@elte.hu> <20050125135613.GA18650@elte.hu> <87sm4opxto.fsf@sulphur.joq.us> <20050126070404.GA27280@elte.hu> <87fz0neshg.fsf@sulphur.joq.us> <1106782165.5158.15.camel@npiggin-nld.site> <20050128080802.GA2860@elte.hu> <871xc62bot.fsf@sulphur.joq.us> <20050128084049.GA5004@elte.hu> From: "Jack O'Quin" Date: Fri, 28 Jan 2005 03:01:28 -0600 In-Reply-To: <20050128084049.GA5004@elte.hu> (Ingo Molnar's message of "Fri, 28 Jan 2005 09:40:49 +0100") Message-ID: <87vf9i0vx3.fsf@sulphur.joq.us> User-Agent: Gnus/5.1006 (Gnus v5.10.6) XEmacs/21.4 (Corporate Culture, linux) 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 Ingo Molnar writes: > * Jack O'Quin wrote: > >> > i'm wondering, couldnt Jackd solve this whole issue completely in >> > user-space, via a simple setuid-root wrapper app that does nothing else >> > but validates whether the user is in the 'jackd' group and then keeps a >> > pipe open to to the real jackd process which it forks off, deprivileges >> > and exec()s? Then unprivileged jackd could request RT-priority changes >> > via that pipe in a straightforward way. Jack normally gets installed as >> > root/admin anyway, so it's not like this couldnt be done. >> >> Perhaps. >> >> Until recently, that didn't work because of the longstanding rlimits >> bug in mlockall(). For scheduling only, it might be possible. >> >> Of course, this violates your requirement that the user not be able to >> lock up the CPU for DoS. The jackd watchdog is not perfect. > > there is a legitimate fear that if it's made "too easy" to acquire some > sort of SCHED_FIFO priority, that an "arm's race" would begin between > desktop apps, each trying to set themselves to SCHED_FIFO (or SCHED_ISO) > and advising users to 'raise the limit if they see delays' - just to get > snappier than the rest. > > thus after a couple of years we'd end up with lots of desktop apps > running as SCHED_FIFO, and latency would go down the drain again. I wonder how Mac OS X and Windows deal with this priority escalation problem? Is it real or only theoretical? -- joq