From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S266054AbUAUEir (ORCPT ); Tue, 20 Jan 2004 23:38:47 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S266055AbUAUEg2 (ORCPT ); Tue, 20 Jan 2004 23:36:28 -0500 Received: from dp.samba.org ([66.70.73.150]:32225 "EHLO lists.samba.org") by vger.kernel.org with ESMTP id S266053AbUAUEfx (ORCPT ); Tue, 20 Jan 2004 23:35:53 -0500 From: Rusty Russell To: Tim Hockin Cc: vatsa@in.ibm.com, lhcs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, torvalds@osdl.org, akpm@osdl.org, rml@tech9.net Subject: Re: CPU Hotplug: Hotplug Script And SIGPWR In-reply-to: Your message of "Tue, 20 Jan 2004 00:37:01 -0800." <20040120083700.GB15733@hockin.org> Date: Wed, 21 Jan 2004 11:12:46 +1100 Message-Id: <20040121043608.740302C10D@lists.samba.org> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org In message <20040120083700.GB15733@hockin.org> you write: > > off). There are no correctness concerns AFAICT with userspace not > > being on a particular CPU, just performance. > > Correctness does matter if an affined task violates that affinity. If we > are going to provide explicit affinity, we need to honor it under all > conditions, or at least provide an option to honor it. WHY? Think of an example where this is actually a problem. "Under all conditions" is not something we can ever implement for anything. > I agree about invasiveness. Maybe a combo? Send SIGPWR iff a task is > actually handling it, otherwise mark it TASK_UNRUNNABLE and let hotplug > handle it? Well, I think that violating affinity given that (1) affinity in userspace is only a performance issue, and (2) we've been explicitly told to take the CPU down, is a valid solution. OTOH making tasks unrunnable until hotplug gets around to servicing them could equally be a disaster. Given that this requires infrastructure not in Linus' tree and the "simply unbind" solution doesn't, I'm leaning towards unbinding everything which would become unrunnable, SIGPWR if they handle it, and hotplug at the end. Thanks, Rusty. -- Anyone who quotes me in their sig is an idiot. -- Rusty Russell.