From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1751833Ab2LZGM1 (ORCPT <rfc822;w@1wt.eu>);
	Wed, 26 Dec 2012 01:12:27 -0500
Received: from LGEMRELSE7Q.lge.com ([156.147.1.151]:58141 "EHLO
	LGEMRELSE7Q.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751297Ab2LZGMY convert rfc822-to-8bit (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Wed, 26 Dec 2012 01:12:24 -0500
X-AuditID: 9c930197-b7c5bae000000e31-9c-50da95467a23
From: Namhyung Kim <namhyung@kernel.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Alessio Igor Bogani <abogani@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>, Avi Kivity <avi@redhat.com>,
        Chris Metcalf <cmetcalf@tilera.com>, Christoph Lameter <cl@linux.com>,
        Geoff Levand <geoff@infradead.org>,
        Gilad Ben Yossef <gilad@benyossef.com>,
        Hakan Akkan <hakanakkan@gmail.com>, Ingo Molnar <mingo@kernel.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Paul Gortmaker <paul.gortmaker@windriver.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 20/24] nohz: Full dynticks mode
References: <1356028391-14427-1-git-send-email-fweisbec@gmail.com>
	<1356028391-14427-21-git-send-email-fweisbec@gmail.com>
Date: Wed, 26 Dec 2012 15:12:22 +0900
In-Reply-To: <1356028391-14427-21-git-send-email-fweisbec@gmail.com> (Frederic
	Weisbecker's message of "Thu, 20 Dec 2012 19:33:07 +0100")
Message-ID: <87a9t1s5o9.fsf@sejong.aot.lge.com>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.1 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8BIT
X-Brightmail-Tracker: AAAAAA==
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Hi Frederic,

On Thu, 20 Dec 2012 19:33:07 +0100, Frederic Weisbecker wrote:
> When a CPU is in full dynticks mode, try to switch
> it to nohz mode from the interrupt exit path if it is
> running a single non-idle task.
>
> Then restart the tick if necessary if we are enqueuing a
> second task while the timer is stopped, so that the scheduler
> tick is rearmed.
>
> [TODO: Check remaining things to be done from scheduler_tick()]
>
> [ Included build fix from Geoff Levand ]
[snip]
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index db3d4df..f3d8f4a 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -943,6 +943,14 @@ static inline u64 steal_ticks(u64 steal)
>  static inline void inc_nr_running(struct rq *rq)
>  {
>  	rq->nr_running++;
> +
> +	if (rq->nr_running == 2) {
> +		if (tick_nohz_full_cpu(rq->cpu)) {
> +			/* Order rq->nr_running write against the IPI */
> +			smp_wmb();
> +			smp_send_reschedule(rq->cpu);
> +		}
> +	}

This block should be guarded with #ifdef CONFIG_SMP, otherwise:

  CC      kernel/sched/core.o
In file included from /home/namhyung/project/linux/kernel/sched/core.c:85:0:
/home/namhyung/project/linux/kernel/sched/sched.h: In function ‘inc_nr_running’:
/home/namhyung/project/linux/kernel/sched/sched.h:960:28: error: ‘struct rq’ has no member named ‘cpu’
/home/namhyung/project/linux/kernel/sched/sched.h:963:26: error: ‘struct rq’ has no member named ‘cpu’


Thanks,
Namhyung

>  }