From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751891AbeCUJl4 (ORCPT ); Wed, 21 Mar 2018 05:41:56 -0400 Received: from mail.cn.fujitsu.com ([183.91.158.132]:19123 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751728AbeCUJlx (ORCPT ); Wed, 21 Mar 2018 05:41:53 -0400 X-IronPort-AV: E=Sophos;i="5.43,368,1503331200"; d="scan'208";a="38036313" Subject: Re: [PATCH 1/5] x86/smpboot: Add the missing description of possible_cpus To: Peter Zijlstra CC: , , , , , , , , , References: <20180320110432.28127-1-douly.fnst@cn.fujitsu.com> <20180320110432.28127-2-douly.fnst@cn.fujitsu.com> <20180320123712.GR4043@hirez.programming.kicks-ass.net> <20180321090826.GW4043@hirez.programming.kicks-ass.net> <076196e1-c181-ba44-f912-61bd279b345b@cn.fujitsu.com> From: Dou Liyang Message-ID: <1dfcdb3d-6a92-8654-7cc4-ef262ddb0915@cn.fujitsu.com> Date: Wed, 21 Mar 2018 17:41:45 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2 MIME-Version: 1.0 In-Reply-To: <076196e1-c181-ba44-f912-61bd279b345b@cn.fujitsu.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.167.226.106] X-yoursite-MailScanner-ID: 5D67F4D0EFC9.AE15B X-yoursite-MailScanner: Found to be clean X-yoursite-MailScanner-From: douly.fnst@cn.fujitsu.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org At 03/21/2018 05:34 PM, Dou Liyang wrote: > Hi Peter, > > At 03/21/2018 05:08 PM, Peter Zijlstra wrote: >> On Wed, Mar 21, 2018 at 01:33:24PM +0800, Dou Liyang wrote: >>> How about: >>> >>> possible_cpus=    [s390,x86_64] Set the number of possible CPUs which >>>         are determined by the ACPI tables MADT or mptables by >>>         default. possible_cpus=n : n >= 1 enforces the possible >>>         number to be 'n'. >>>         While nr_cpus is also be set: nr_cpus=m, choice the >>>         minimum one for the number of possible CPUs. >> >> So what is the exact difference between possible_cpus and nr_cpus ? I > > the possible_cpus= can reset the number of possible CPUs, even bigger > than 'num_processors + disabled_cpus', But nr_cpus= can't. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the maximum number kernel gets from ACPI/mptables, no matter what number nr_cpus= is, the number of possible CPUs will not bigger than it. > >> konw maxcpus= limits the number of CPUs we bring up, and possible_cpus >> limits the possible_map, but I'm not entirely sure what nr_cpus does >> here. >> > > nr_cpus can limited the maximum CPUs that the kernel could support. > > Here is a double check in case of using them at the same time, even if I > think just using possible_cpus= is enough. :-) > > Thanks, >     dou. >> >>