linux-kernel - Re: [PATCH 2/7] sched, preempt: Fixup missed PREEMPT_NEED

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Date:	Thu, 21 Nov 2013 09:25:28 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Arjan van de Ven <arjan@...ux.intel.com>, lenb@...nel.org,
	rjw@...ysocki.net, Eliezer Tamir <eliezer.tamir@...ux.intel.com>,
	Chris Leech <christopher.leech@...el.com>,
	David Miller <davem@...emloft.net>, rui.zhang@...el.com,
	jacob.jun.pan@...ux.intel.com,
	Mike Galbraith <bitbucket@...ine.de>,
	Ingo Molnar <mingo@...nel.org>, hpa@...or.com,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH 2/7] sched, preempt: Fixup missed PREEMPT_NEED_RESCHED
 folding

On Wed, Nov 20, 2013 at 05:04:52PM +0100, Peter Zijlstra wrote:
> --- a/kernel/cpu/idle.c
> +++ b/kernel/cpu/idle.c
> @@ -105,14 +105,14 @@ static void cpu_idle_loop(void)
>  				__current_set_polling();
>  			}
>  			arch_cpu_idle_exit();
> -			/*
> -			 * We need to test and propagate the TIF_NEED_RESCHED
> -			 * bit here because we might not have send the
> -			 * reschedule IPI to idle tasks.
> -			 */
> -			if (tif_need_resched())
> -				set_preempt_need_resched();
>  		}


		/*
		 * Ensure our read doesn't slip before the read that
		 * terminates the loop above; in that situation we might
		 * actually fail to observe the TIF_NEED_RESCHED we
		 * _know_ must be set here.
		 */

		smp_rmb(); /* pairs with resched_task() */

> +
> +		/*
> +		 * We need to test and propagate the TIF_NEED_RESCHED bit here
> +		 * because we might not have send the reschedule IPI to idle
> +		 * tasks.
> +		 */
> +		preempt_fold_need_resched();
>  		tick_nohz_idle_exit();
>  		schedule_preempt_disabled();
>  	}
--
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