linux-kernel - Re: [PATCH 20/24] nohz: Full dynticks mode

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Date:	Wed, 26 Dec 2012 15:12:22 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Alessio Igor Bogani <abogani@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Avi Kivity <avi@...hat.com>,
	Chris Metcalf <cmetcalf@...era.com>,
	Christoph Lameter <cl@...ux.com>,
	Geoff Levand <geoff@...radead.org>,
	Gilad Ben Yossef <gilad@...yossef.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 20/24] nohz: Full dynticks mode

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

>  }
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