From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751078AbWGFXuP (ORCPT ); Thu, 6 Jul 2006 19:50:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751082AbWGFXuP (ORCPT ); Thu, 6 Jul 2006 19:50:15 -0400 Received: from omta03sl.mx.bigpond.com ([144.140.92.155]:46422 "EHLO omta03sl.mx.bigpond.com") by vger.kernel.org with ESMTP id S1751078AbWGFXuN (ORCPT ); Thu, 6 Jul 2006 19:50:13 -0400 Message-ID: <44ADA1B3.1080506@bigpond.net.au> Date: Fri, 07 Jul 2006 09:50:11 +1000 From: Peter Williams User-Agent: Thunderbird 1.5.0.4 (X11/20060614) MIME-Version: 1.0 To: Mike Galbraith CC: Andrew Morton , Nick Piggin , Linux Kernel , Con Kolivas , Ingo Molnar Subject: Re: [PATCH] sched: Add SCHED_BGND (background) scheduling policy References: <20060704233521.8744.45368.sendpatchset@heathwren.pw.nest> <1152099752.8684.198.camel@Homer.TheSimpsons.net> <44ABC5B7.2090707@bigpond.net.au> <1152110907.8594.19.camel@Homer.TheSimpsons.net> In-Reply-To: <1152110907.8594.19.camel@Homer.TheSimpsons.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Authentication-Info: Submitted using SMTP AUTH PLAIN at omta03sl.mx.bigpond.com from [147.10.133.38] using ID pwil3058@bigpond.net.au at Thu, 6 Jul 2006 23:50:11 +0000 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Mike Galbraith wrote: > On Wed, 2006-07-05 at 23:59 +1000, Peter Williams wrote: >> Mike Galbraith wrote: >>> The task in the expired array could also be a !safe_to_background() task >>> who already had a chance to run, and who's slice expired. >> If it's !safe_to_background() it's in our interest to let it run in >> order to free up the resource that it's holding. > > Only if there are waiters (or you know there will be some before the > holder gets a chance to run again). Even then, they might be background > tasks, so it could still be ~wrong. > > (yeah, comprehensive PI would be mucho tidier than tick time) Yes. Unfortunately, in Ingo's opinion, even if we have comprehensive PI it's unlikely to be reliable enough to guarantee putting tasks into the background is safe. Of course, this wouldn't detract from its general usefulness -- just makes it no good for SCHED_BGND/SCHED_IDLEPRIO purposes. Peter -- Peter Williams pwil3058@bigpond.net.au "Learning, n. The kind of ignorance distinguishing the studious." -- Ambrose Bierce