Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752715Ab2FRROF (ORCPT ); Mon, 18 Jun 2012 13:14:05 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:35690 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751877Ab2FRROC (ORCPT ); Mon, 18 Jun 2012 13:14:02 -0400 Date: Mon, 18 Jun 2012 10:05:54 -0700 From: "Paul E. McKenney" To: Yong Zhang Cc: linux-kernel@vger.kernel.org, ralf@linux-mips.org, sshtylyov@mvista.com, david.daney@cavium.com, nikunj@linux.vnet.ibm.com, axboe@kernel.dk, mingo@kernel.org, tglx@linutronix.de, peterz@infradead.org, akpm@linux-foundation.org, srivatsa.bhat@linux.vnet.ibm.com, Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev@lists.ozlabs.org Subject: Re: [RFC PATCH 09/10] POWERPC: smp: remove call to ipi_call_lock()/ipi_call_unlock() Message-ID: <20120618170554.GE2400@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1338275765-3217-1-git-send-email-yong.zhang0@gmail.com> <1338275765-3217-10-git-send-email-yong.zhang0@gmail.com> <20120616163219.GI2420@linux.vnet.ibm.com> <20120618025159.GA24420@zhy> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120618025159.GA24420@zhy> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12061817-7182-0000-0000-000001C48DAA Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3199 Lines: 90 On Mon, Jun 18, 2012 at 10:51:59AM +0800, Yong Zhang wrote: > On Sat, Jun 16, 2012 at 09:32:19AM -0700, Paul E. McKenney wrote: > > On Tue, May 29, 2012 at 03:16:04PM +0800, Yong Zhang wrote: > > > From: Yong Zhang > > > > > > 1) call_function.lock used in smp_call_function_many() is just to protect > > > call_function.queue and &data->refs, cpu_online_mask is outside of the > > > lock. And it's not necessary to protect cpu_online_mask, > > > because data->cpumask is pre-calculate and even if a cpu is brougt up > > > when calling arch_send_call_function_ipi_mask(), it's harmless because > > > validation test in generic_smp_call_function_interrupt() will take care > > > of it. > > > > > > 2) For cpu down issue, stop_machine() will guarantee that no concurrent > > > smp_call_fuction() is processing. > > > > However, there is an effort to get rid of stop_machine() from the > > CPU-down path... So something else will be needed. > > Yeah. So Thomas changed the commit log like below: > [ > ipi_call_lock/unlock() lock resp. unlock call_function.lock. This lock > protects only the call_function data structure itself, but it's > completely unrelated to cpu_online_mask. The mask to which the IPIs > are sent is calculated before call_function.lock is taken in > smp_call_function_many(), so the locking around set_cpu_online() is > pointless and can be removed. > > [ tglx: Massaged changelog ] > ] > > in tip/smp/hotplug. Got it, thank you! Thanx, Paul > Thanks, > Yong > > > > > Thanx, Paul > > > > > Signed-off-by: Yong Zhang > > > Cc: Benjamin Herrenschmidt > > > Cc: Paul Mackerras > > > Cc: linuxppc-dev@lists.ozlabs.org > > > --- > > > arch/powerpc/kernel/smp.c | 2 -- > > > 1 files changed, 0 insertions(+), 2 deletions(-) > > > > > > diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c > > > index e4cb343..e1417c4 100644 > > > --- a/arch/powerpc/kernel/smp.c > > > +++ b/arch/powerpc/kernel/smp.c > > > @@ -571,7 +571,6 @@ void __devinit start_secondary(void *unused) > > > if (system_state == SYSTEM_RUNNING) > > > vdso_data->processorCount++; > > > #endif > > > - ipi_call_lock(); > > > notify_cpu_starting(cpu); > > > set_cpu_online(cpu, true); > > > /* Update sibling maps */ > > > @@ -601,7 +600,6 @@ void __devinit start_secondary(void *unused) > > > of_node_put(np); > > > } > > > of_node_put(l2_cache); > > > - ipi_call_unlock(); > > > > > > local_irq_enable(); > > > > > > -- > > > 1.7.5.4 > > > > > > > -- > > 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/ > > -- > Only stand for myself > -- 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/