Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753670AbYH1LG7 (ORCPT ); Thu, 28 Aug 2008 07:06:59 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751998AbYH1LGv (ORCPT ); Thu, 28 Aug 2008 07:06:51 -0400 Received: from one.firstfloor.org ([213.235.205.2]:52803 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751869AbYH1LGv (ORCPT ); Thu, 28 Aug 2008 07:06:51 -0400 Date: Thu, 28 Aug 2008 13:09:23 +0200 From: Andi Kleen To: Ingo Molnar Cc: Nick Piggin , Andi Kleen , Thomas Gleixner , Peter Zijlstra , linux-kernel@vger.kernel.org, Stefani Seibold , Dario Faggioli , Max Krasnyansky , Linus Torvalds Subject: Re: [PATCH 6/6] sched: disabled rt-bandwidth by default Message-ID: <20080828110923.GL26610@one.firstfloor.org> References: <20080819103301.787700742@chello.nl> <874p57s873.fsf@basil.nowhere.org> <200808272008.16106.nickpiggin@yahoo.com.au> <20080828105408.GA4488@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080828105408.GA4488@elte.hu> User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1299 Lines: 29 > Even if the system has multiple CPUs, and even if just a single CPU is > fully utilized by an RT task, without the rt-limit the system will still > lock up in practice due to various other factors: workqueues and tasks > being 'stuck' on CPUs that host an RT hog. The load balancer will not notice that a particular CPU is busy with real time tasks? > While there's obviously CPU > time available on other CPUs, you cannot run 'top', the desktop will > freeze, work flows of the system can be stuck, etc, etc.. I had such a situation at least once in the past (not due run away RT but due a kernel bug) and even with 2 out of 4 CPUs blocked the system was still quite usable. top/kill definitely worked. The system didn't have a desktop, but I didn't notice many problems in shell use. Ok it's just one sample. That said I don't think having such a limit by default is a bad idea actually. Just handling it in the scheduler anyways is also probably good because it can happen even due to other issues than just run away RT tasks. -Andi -- 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/