linux-kernel - Re: [PATCH 27/35] sched/idle: Use explicit broadcast oneshot control function

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Date:	Fri, 20 Feb 2015 19:56:17 -0500 (EST)
From:	Nicolas Pitre <nico@...aro.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org, rjw@...ysocki.net,
	tglx@...utronix.de
Subject: Re: [PATCH 27/35] sched/idle: Use explicit broadcast oneshot control
 function

On Mon, 16 Feb 2015, Peter Zijlstra wrote:

> From: Thomas Gleixner <tglx@...utronix.de>
> 
> Replace the clockevents_notify() call with an explicit function call.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

This patch makes my test system hang solid after letting it sit idle for 
5 to 15 minutes.  Reverting it and this issue goes away.

The explicit function call is not an equivalent replacement. In 
clockevents_notify() the clockevents_lock is held across the call to 
tick_broadcast_enter() or tick_broadcast_exit(). This patch drops the 
locking.

> ---
>  kernel/sched/idle.c |    5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> Index: linux/kernel/sched/idle.c
> ===================================================================
> --- linux.orig/kernel/sched/idle.c
> +++ linux/kernel/sched/idle.c
> @@ -143,8 +143,7 @@ use_default:
>  	 * is used from another cpu as a broadcast timer, this call may
>  	 * fail if it is not available
>  	 */
> -	if (broadcast &&
> -	    clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &dev->cpu))
> +	if (broadcast && tick_broadcast_enter())
>  		goto use_default;
>  
>  	/* Take note of the planned idle state. */
> @@ -161,7 +160,7 @@ use_default:
>  	idle_set_state(this_rq(), NULL);
>  
>  	if (broadcast)
> -		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &dev->cpu);
> +		tick_broadcast_exit();
>  
>  	/*
>  	 * Give the governor an opportunity to reflect on the outcome
> 
> 
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