From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751914AbdHGPKc (ORCPT ); Mon, 7 Aug 2017 11:10:32 -0400 Received: from bombadil.infradead.org ([65.50.211.133]:37735 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751722AbdHGPK3 (ORCPT ); Mon, 7 Aug 2017 11:10:29 -0400 Date: Mon, 7 Aug 2017 17:10:20 +0200 From: Peter Zijlstra To: "Ofer Levi(SW)" Cc: "rusty@rustcorp.com.au" , "vatsa@in.ibm.com" , "mingo@redhat.com" , "Vineet.Gupta1@synopsys.com" , "linux-kernel@vger.kernel.org" Subject: Re: hotplug support for arch/arc/plat-eznps platform Message-ID: <20170807151020.h2u45tx64ccee64a@hirez.programming.kicks-ass.net> References: <20170807083354.ptkehfql54xydsvm@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 07, 2017 at 01:41:38PM +0000, Ofer Levi(SW) wrote: > > You've failed to explain why you think hotplug should be a performance > > critical path. > 1. hotplug bring up of 4K cpus takes 40 minutes. Way too much for any user. > 2. plat-eznps is a network processor, where bring up time is sensitive. But who is doing actual hotplug? Why would you ever unplug or plug a CPU in a time critical situation? > > I'm also not seeing how it would be different from boot; you'd be > > looking at a similar cost for SMP bringup. > bring up time of 4k cpus during kernel boot takes 4.5 minutes. > The function in question is performed only when smp init was performed. > If I understand correctly, whatever this function is doing is performed after all cpus > were brought up during kernel boot. Doesn't make sense. If you look at smp_init() boot brings up the CPUs one at a time. So how can boot be different than hot-pugging them?