linux-kernel - Re: [PATCH 3/6] sched,idle: Clarify where TIF_NRFLAG

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Message-ID: <538F1936.4000905@linaro.org>
Date:	Wed, 04 Jun 2014 15:03:50 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Andy Lutomirski <luto@...capital.net>,
	Peter Zijlstra <peterz@...radead.org>, umgwanakikbuti@...il.com
CC:	mingo@...nel.org, tglx@...utronix.de, nicolas.pitre@...aro.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] sched,idle: Clarify where TIF_NRFLAG_POLLING is set

On 06/04/2014 02:29 AM, Andy Lutomirski wrote:
> This doesn't change functionality at all, but I've misread this code
> so many times that I want to make it a bit more obvious.
>
> Signed-off-by: Andy Lutomirski <luto@...capital.net>
> ---
>   kernel/sched/idle.c | 12 +++++++++++-
>   1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> index 25b9423..2ec9f47 100644
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -67,6 +67,10 @@ void __weak arch_cpu_idle(void)
>    * cpuidle_idle_call - the main idle function
>    *
>    * NOTE: no locks or semaphores should be used here
> + *
> + * On archs that support TIF_POLLING_NRFLAG, is called with polling
> + * set, and it returns with polling set.  If it ever stops polling, it
> + * must clear the polling bit.
>    */
>   static void cpuidle_idle_call(void)
>   {
> @@ -178,7 +182,14 @@ exit_idle:
>    */
>   static void cpu_idle_loop(void)
>   {
> +	__current_set_polling();
> +
>   	while (1) {
> +		/*
> +		 * Invariant: polling is set here (assuming that the arch
> +		 * has a polling bit.
> +		 */
> +

nit : extra line

>   		tick_nohz_idle_enter();
>
>   		while (!need_resched()) {
> @@ -239,7 +250,6 @@ void cpu_startup_entry(enum cpuhp_state state)
>   	 */
>   	boot_init_stack_canary();
>   #endif
> -	__current_set_polling();

I don't get the connection with the patch description.

>   	arch_cpu_idle_prepare();
>   	cpu_idle_loop();
>   }
>


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