Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758595Ab0BRR0g (ORCPT ); Thu, 18 Feb 2010 12:26:36 -0500 Received: from terminus.zytor.com ([198.137.202.10]:43232 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757583Ab0BRR0e (ORCPT ); Thu, 18 Feb 2010 12:26:34 -0500 Message-ID: <4B7D782F.20102@zytor.com> Date: Thu, 18 Feb 2010 09:26:07 -0800 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.7) Gecko/20100120 Fedora/3.0.1-1.fc12 Thunderbird/3.0.1 MIME-Version: 1.0 To: Yinghai Lu CC: Ingo Molnar , Thomas Gleixner , Andrew Morton , Linus Torvalds , Jesse Barnes , Christoph Lameter , linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, Suresh Siddha Subject: Re: [PATCH 34/35] x86: use num_processors for possible cpus References: <1265793639-15071-1-git-send-email-yinghai@kernel.org> <1265793639-15071-35-git-send-email-yinghai@kernel.org> <4B7C98B9.1090903@zytor.com> <4B7CA825.9090309@kernel.org> In-Reply-To: <4B7CA825.9090309@kernel.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1276 Lines: 36 On 02/17/2010 06:38 PM, Yinghai Lu wrote: >> >> I'm confused by this one. This would seem to mean that unless you're >> specifying possible_cpus= then you are not treating anything as >> hotpluggable. >> >> This is clearly wrong, and it would appear to go the wrong direction in >> terms of what is safe. >> >> What am I missing here? > > per_cpu setup will allocate some mem for every cpu according to possible cpus. > Yes, and I have repeatedly requested that we allocate the memory on the first up of a disabled CPU rather than eagerly, but in *most* configurations the amount is relatively small. > no spec says that we should disable cpus entries in MADT as hotplug cpus. Reality seems to, though. Consider the bug report that led to patch 681ee44d40d7c93b42118320e4620d07d8704fd6 for example. > also how many system that support hotplug cpus there? In terms of physical machines, not all that many; however, it is getting common to use CPU hotplug for virtual environments so they can be dynamically scaled. -hpa -- 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/