Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762298AbYBLSrM (ORCPT ); Tue, 12 Feb 2008 13:47:12 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759255AbYBLSq6 (ORCPT ); Tue, 12 Feb 2008 13:46:58 -0500 Received: from one.firstfloor.org ([213.235.205.2]:33105 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758641AbYBLSq5 (ORCPT ); Tue, 12 Feb 2008 13:46:57 -0500 Date: Tue, 12 Feb 2008 20:22:27 +0100 From: Andi Kleen To: Linus Torvalds Cc: Andi Kleen , Ingo Molnar , linux-kernel@vger.kernel.org, "Frank Ch. Eigler" , Roland McGrath , Thomas Gleixner , "H. Peter Anvin" , Andrew Morton Subject: Re: [git pull] kgdb-light -v10 Message-ID: <20080212192227.GB6458@one.firstfloor.org> References: <20080211230335.GA16102@elte.hu> <20080212100327.GA30873@one.firstfloor.org> <20080212112747.GA1569@elte.hu> <20080212121903.GA419@one.firstfloor.org> <20080212123839.GA15360@elte.hu> <20080212135027.GA1343@one.firstfloor.org> <20080212152846.GC3078@elte.hu> <20080212182024.GA4940@one.firstfloor.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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: 1502 Lines: 36 On Tue, Feb 12, 2008 at 10:11:13AM -0800, Linus Torvalds wrote: > > > On Tue, 12 Feb 2008, Andi Kleen wrote: > > > > > - the kgdb commands should always act on the *current* CPU only > > > - add one command that says "switch over to CPU #n" which just releases > > > the current CPU and sends an IPI to that CPU #n (no timeouts, no > > > synchronous waiting, no nothing - it's like a "continue", but with a > > > "try to get the other CPU to stop" > > > > The problem I see here is that the kernel tends to get badly confused > > if one CPU just stops responding. At some point someone does an global > > IPI and that then hangs. You would need to hotunplug the CPU which > > is theoretically possible, but quite intrusive. > > You're thinking about this totally *wrong*. > > You definitely do not want to hot-unplug or isolate anything at all. I agree that it wouldn't be a good idea -- i was just pointing out consequences of your proposal. > Just let the other CPU's hang naturally if they need to wait for IPI's > etc. What's the downside? There tend to be timeouts (e.g. softlock/nmi watchdog at least). I think some of the IPIs eventually time out too. In general losing a lot of time can lead to weird side effects. -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/