Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754072AbaDNOv0 (ORCPT ); Mon, 14 Apr 2014 10:51:26 -0400 Received: from mail-ee0-f45.google.com ([74.125.83.45]:60604 "EHLO mail-ee0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751161AbaDNOvY (ORCPT ); Mon, 14 Apr 2014 10:51:24 -0400 Date: Mon, 14 Apr 2014 16:51:19 +0200 From: Ingo Molnar 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 Subject: Re: [PATCH v3 1/5] x86: initialize secondary CPU only if master CPU will wait for it Message-ID: <20140414145119.GA27683@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> <20140414100335.GC731@gmail.com> <20140414145048.3d7cf907@nial.usersys.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140414145048.3d7cf907@nial.usersys.redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Igor Mammedov wrote: > On Mon, 14 Apr 2014 12:03:35 +0200 > Ingo Molnar wrote: > > > > > * 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.) > > WARN_ON will never be triggered here since bit is always cleared by > master CPU before AP gets here. There is no harm keeping WARN_ON > though, do you still want it be here? The previous code panic()ed on this condition - so it makes sense to at least keep a WARN_ON(). That it won't ever trigger is good: > It could be useful to put WARN_ON in do_boot_cpu() before bit is > cleared, so that user would see that he tries to online AP which has > failed previous time. It's not really necessary since failed to > online attempt reported in logs at ERR level now, see patch 2/5. WARN_ON()s are not used to communicate with users, they are used to show developers that there's a _bug_ in the code! So a WARN_ON() not triggering, ever, is a good thing. Thanks, Ingo -- 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/