Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755375Ab3FLNuj (ORCPT ); Wed, 12 Jun 2013 09:50:39 -0400 Received: from mga14.intel.com ([143.182.124.37]:38833 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752316Ab3FLNui (ORCPT ); Wed, 12 Jun 2013 09:50:38 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.87,852,1363158000"; d="scan'208";a="315872827" Date: Wed, 12 Jun 2013 21:36:09 -0400 From: Youquan Song To: "Rafael J. Wysocki" Cc: Yinghai Lu , Youquan Song , Greg Kroah-Hartman , Andrew Morton , Dave Hansen , Toshi Kani , Youquan Song , LKML , Stephen Rothwell Subject: Re: cpu hotplug: possible_cpus broken (again?) next-20130607 Message-ID: <20130613013609.GA6348@linux-youquan.bj.intel.com> References: <51B79BE5.80804@sr71.net> <20130612123248.GA23978@linux-youquan.bj.intel.com> <4005805.V3phb1agMs@vostro.rjw.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4005805.V3phb1agMs@vostro.rjw.lan> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2313 Lines: 60 > > Interesting, you are changing long standing meaning of maxcpus= > > > > We always use maxcpus=1 to have one cpu up, and later in user space > > to online other cpus like > > echo 1 > /sys/devices/system/cpuX/online. > > > > aka maxcpus= is a soft limit or initial online nr. > > > > we already have nr_cpus= for hard limit. > > > > So need to drop > > commit 3e275a5ba367ab74b3a4e49114307baed989fcac > > Author: Youquan Song > > Date: Fri Jun 7 10:07:08 2013 +1000 > > > > drivers/base/cpu.c: fix maxcpus boot option > > Agreed. Yes. I also agree to drop it and the fix need more consideration. I try use maxcpus to limit cpu number to debug a well known applition because it fail to run when cpu number is larger to > 69. When I use maxcpus at to limit the boot CPUs number, but udev will enable all of the CPUs at 3.10 kernel automatically. I also try maxcpus at 3.0 kernel, it does not show the maxcpus issue. I have digged out recently, it is the commit at 3.2 kernel 8a25a2fd126c621f44f3aeaef80d51f00fc11639 "cpu: convert 'cpu' and 'machinecheck' sysdev_class to a regular subsystem" result in udev automatically enable all of CPUs though maxcpus has been provided. So the next, I need look at udev try to enable all of CPUs though maxcpus provided. Possibly, it can also fix it in udev daemon. Secondly, I think that the maxcpus= option description is too confused in Documentation/kernel-parameters.txt. The maxcpus and nr_cpus option need switch their name. Currently: maxcpus= [SMP] Maximum number of processors that an SMP kernel should make use of. maxcpus=n : n >= 0 limits the kernel to using 'n' processors. n=0 is a special case, it is equivalent to "nosmp", which also disables the IO APIC. How about change to maxcpus= [SMP] Maximum number of processors that an SMP kernel bring up during booting. maxcpus=n : n >= 0 limits the kernel to using 'n' processors. n=0 is a special case, it is equivalent to "nosmp", which also disables the IO APIC. Thanks -Youquan -- 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/