From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751551AbdAQXhT (ORCPT ); Tue, 17 Jan 2017 18:37:19 -0500 Received: from pandora.armlinux.org.uk ([78.32.30.218]:33218 "EHLO pandora.armlinux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751095AbdAQXhB (ORCPT ); Tue, 17 Jan 2017 18:37:01 -0500 Date: Tue, 17 Jan 2017 23:23:14 +0000 From: Russell King - ARM Linux To: Florian Fainelli Cc: linux-arm-kernel@lists.infradead.org, Petr Mladek , Chris Metcalf , open list , Aaron Tomlin , Andrew Morton , "Paul E. McKenney" , Thomas Gleixner , Kees Cook Subject: Re: [PATCH] ARM: smp: Remove CPU: shutdown notice Message-ID: <20170117232314.GI27312@n2100.armlinux.org.uk> References: <20170117230714.6799-1-f.fainelli@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170117230714.6799-1-f.fainelli@gmail.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 17, 2017 at 03:07:12PM -0800, Florian Fainelli wrote: > This message is not particularly informative, and is not paired with an > identical message when a CPU is brought online. Finally, it slows the > CPU hotplug path down, thus allowing less CPU hotplug operations per > second. Just remove it. CPU hotplug isn't a fast operation anyway - it's also fairly disruptive in that it uses stop_machine() to halt activity everywhere while taking the CPU offline. If you're worried about a single printk slowing things down, it sounds like you're doing something wrong here - maybe you should be using cpuidle for power management rather than trying to make CPU hotplug do that for you? A rapidly changing CPU hotplug state has other side effects - such as reading /proc/interrupts is meaningless, because as soon as you've read it the CPUs could have changed. It also makes a farce of spreading interrupts over the available CPUs. All in all, I don't think this is a good idea... -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.