From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [PATCH v3 1/5] x86: initialize secondary CPU only if master CPU will wait for it Date: Mon, 14 Apr 2014 12:03:35 +0200 Message-ID: <20140414100335.GC731@gmail.com> References: <1397150061-29735-1-git-send-email-imammedo@redhat.com> <1397150061-29735-2-git-send-email-imammedo@redhat.com> <20140414091600.GA19771@gmail.com> <20140414115210.51193098@thinkpad> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail-bk0-f54.google.com ([209.85.214.54]:40998 "EHLO mail-bk0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750790AbaDNKDk (ORCPT ); Mon, 14 Apr 2014 06:03:40 -0400 Content-Disposition: inline In-Reply-To: <20140414115210.51193098@thinkpad> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Igor Mammedov Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, x86@kernel.org, bp@suse.de, paul.gortmaker@windriver.com, JBeulich@suse.com, prarit@redhat.com, drjones@redhat.com, toshi.kani@hp.com, riel@redhat.com, gong.chen@linux.intel.com, andi@firstfloor.org, lenb@kernel.org, rjw@rjwysocki.net, linux-acpi@vger.kernel.org * Igor Mammedov wrote: > On Mon, 14 Apr 2014 11:16:00 +0200 > Ingo Molnar wrote: > > > > > * Igor Mammedov wrote: > > > > > /* > > > + * wait for ACK from master CPU before continuing > > > + * with AP initialization > > > + */ > > > + cpumask_set_cpu(cpu, cpu_initialized_mask); > > > + while (!cpumask_test_cpu(cpu, cpu_callout_mask)) > > > + cpu_relax(); > > > > > + /* > > > + * wait for ACK from master CPU before continuing > > > + * with AP initialization > > > + */ > > > + cpumask_set_cpu(cpu, cpu_initialized_mask); > > > + while (!cpumask_test_cpu(cpu, cpu_callout_mask)) > > > + cpu_relax(); > > > > That repetitive pattern could be stuck into a properly named helper > > inline function. > sure > > > (Also, before the cpumask_set_cpu() we should probably do a WARN_ON() > > if the bit is already set.) > The reason why there is no any WARN_ON or likes is that printk is quite > complicated, takes looks and so on. [...] [ Yeah, I too heard that printk(), like a pretty girl, is complicated and makes people look twice. ] > [...] So it's not safe at this point since > CPU could be shot down by any time by INIT/SIPI until it's out of > cpu_callout_mask loop. Not sure where you got that from, but it's not a valid concern really: the only place where we don't want to do a printk() is in printk code itself. Debug warnings, by definition, should never trigger. If they trigger then they will very likely not cause lockups, but will cause the bug to be fixed. Thanks, Ingo