From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH v2 3/5] kernel/cpu: Allow non-zero CPU to be primary for suspend / kexec freeze Date: Thu, 25 Apr 2019 14:02:21 +0200 Message-ID: <20190425120221.GR4038@hirez.programming.kicks-ass.net> References: <20190411033448.20842-1-npiggin@gmail.com> <20190411033448.20842-4-npiggin@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20190411033448.20842-4-npiggin@gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: Nicholas Piggin Cc: Thomas Gleixner , Frederic Weisbecker , Ingo Molnar , "Rafael J . Wysocki" , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org List-Id: linux-arch.vger.kernel.org On Thu, Apr 11, 2019 at 01:34:46PM +1000, Nicholas Piggin wrote: > This patch provides an arch option, ARCH_SUSPEND_NONZERO_CPU, to > opt-in to allowing suspend to occur on one of the housekeeping CPUs > rather than hardcoded CPU0. > > This will allow CPU0 to be a nohz_full CPU with a later change. > > It may be possible for platforms with hardware/firmware restrictions > on suspend/wake effectively support this by handing off the final > stage to CPU0 when kernel housekeeping is no longer required. Another > option is to make housekeeping / nohz_full mask dynamic at runtime, > but the complexity could not be justified at this time. Should we not tie this into whatever already allows an achitecture to hotplug CPU-0? For instance, x86 default disallows this but has cpu0_hotpluggable to allow this. Presumably POWER already allows hotplugging CPU-0 ? From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org ([198.137.202.133]:33932 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726303AbfDYMC2 (ORCPT ); Thu, 25 Apr 2019 08:02:28 -0400 Date: Thu, 25 Apr 2019 14:02:21 +0200 From: Peter Zijlstra Subject: Re: [PATCH v2 3/5] kernel/cpu: Allow non-zero CPU to be primary for suspend / kexec freeze Message-ID: <20190425120221.GR4038@hirez.programming.kicks-ass.net> References: <20190411033448.20842-1-npiggin@gmail.com> <20190411033448.20842-4-npiggin@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190411033448.20842-4-npiggin@gmail.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Nicholas Piggin Cc: Thomas Gleixner , Frederic Weisbecker , Ingo Molnar , "Rafael J . Wysocki" , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Message-ID: <20190425120221.2HshMA7nLBEckjxVEaLQrmsOZWpp3-6KvBUGyW-4iWY@z> On Thu, Apr 11, 2019 at 01:34:46PM +1000, Nicholas Piggin wrote: > This patch provides an arch option, ARCH_SUSPEND_NONZERO_CPU, to > opt-in to allowing suspend to occur on one of the housekeeping CPUs > rather than hardcoded CPU0. > > This will allow CPU0 to be a nohz_full CPU with a later change. > > It may be possible for platforms with hardware/firmware restrictions > on suspend/wake effectively support this by handing off the final > stage to CPU0 when kernel housekeeping is no longer required. Another > option is to make housekeeping / nohz_full mask dynamic at runtime, > but the complexity could not be justified at this time. Should we not tie this into whatever already allows an achitecture to hotplug CPU-0? For instance, x86 default disallows this but has cpu0_hotpluggable to allow this. Presumably POWER already allows hotplugging CPU-0 ?