Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964970Ab2HVR1f (ORCPT ); Wed, 22 Aug 2012 13:27:35 -0400 Received: from e34.co.us.ibm.com ([32.97.110.152]:54419 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964952Ab2HVR1b (ORCPT ); Wed, 22 Aug 2012 13:27:31 -0400 Date: Wed, 22 Aug 2012 10:19:30 -0700 From: "Paul E. McKenney" To: Frederic Weisbecker Cc: LKML , Richard Henderson , Ivan Kokshaysky , Matt Turner , alpha , "3.2.x.." Subject: Re: [PATCH 01/10] alpha: Add missing RCU idle APIs on idle loop Message-ID: <20120822171930.GE2447@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1345652628-15060-1-git-send-email-fweisbec@gmail.com> <1345652628-15060-2-git-send-email-fweisbec@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1345652628-15060-2-git-send-email-fweisbec@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12082217-1780-0000-0000-000008A2C066 X-IBM-ISS-SpamDetectors: X-IBM-ISS-DetailInfo: BY=3.00000293; HX=3.00000196; KW=3.00000007; PH=3.00000001; SC=3.00000007; SDB=6.00167565; UDB=6.00037959; UTC=2012-08-22 17:27:27 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2419 Lines: 76 On Wed, Aug 22, 2012 at 06:23:39PM +0200, Frederic Weisbecker wrote: > In the old times, the whole idle task was considered > as an RCU quiescent state. But as RCU became more and > more successful overtime, some RCU read side critical > section have been added even in the code of some > architectures idle tasks, for tracing for example. > > So nowadays, rcu_idle_enter() and rcu_idle_exit() must > be called by the architecture to tell RCU about the part > in the idle loop that doesn't make use of rcu read side > critical sections, typically the part that puts the CPU > in low power mode. > > This is necessary for RCU to find the quiescent states in > idle in order to complete grace periods. > > Add this missing pair of calls in the Alpha's idle loop. > > Reported-by: Paul E. McKenney > Signed-off-by: Frederic Weisbecker > Cc: Richard Henderson > Cc: Ivan Kokshaysky > Cc: Matt Turner > Cc: alpha > Cc: Paul E. McKenney > Cc: 3.2.x.. > --- > arch/alpha/kernel/process.c | 6 +++++- > 1 files changed, 5 insertions(+), 1 deletions(-) > > diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c > index 153d3fc..2ebf7b5 100644 > --- a/arch/alpha/kernel/process.c > +++ b/arch/alpha/kernel/process.c > @@ -28,6 +28,7 @@ > #include > #include > #include > +#include > > #include > #include > @@ -50,13 +51,16 @@ cpu_idle(void) > { > set_thread_flag(TIF_POLLING_NRFLAG); > > + preempt_disable(); I don't understand the above preempt_disable() not having a matching preempt_enable() at exit, but the rest of the patches in this series look good to me. Thanx, Paul > while (1) { > /* FIXME -- EV6 and LCA45 know how to power down > the CPU. */ > > + rcu_idle_enter(); > while (!need_resched()) > cpu_relax(); > - schedule(); > + rcu_idle_exit(); > + schedule_preempt_disabled(); > } > } > > -- > 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/