linux-kernel - Re: [PATCH 1/2] sched/wait: add wait_event

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Date:   Fri, 22 Dec 2017 09:06:56 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     NeilBrown <neilb@...e.com>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        lustre <lustre-devel@...ts.lustre.org>
Subject: Re: [PATCH 1/2] sched/wait: add wait_event_idle() functions.

On Fri, Dec 22, 2017 at 02:11:04PM +1100, NeilBrown wrote:
> The new TASK_IDLE state (TASK_UNINTERRUPTIBLE | __TASK_NOLOAD)
> is not much used.  One way to make it easier to use is to
> add wait_event*() family functions that make use of it.
> This patch adds:
>   wait_event_idle()
>   wait_event_idle_timeout()
>   wait_event_idle_exclusive()
> 
> This set were chosen because lustre needs them before
> it can discard its own l_wait_event() macro.

Seems sane enough; please take through the tree that introduces the
first users of this.

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

> Signed-off-by: NeilBrown <neilb@...e.com>
> ---
>  include/linux/wait.h |   77 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 77 insertions(+)
> 
> diff --git a/include/linux/wait.h b/include/linux/wait.h
> index 158715445ffb..3aea0780c9d0 100644
> --- a/include/linux/wait.h
> +++ b/include/linux/wait.h
> @@ -597,6 +597,83 @@ do {										\
>  	__ret;									\
>  })
>  
> +/**
> + * wait_event_idle - wait for a condition with contributing to system load
> + * @wq_head: the waitqueue to wait on
> + * @condition: a C expression for the event to wait for
> + *
> + * The process is put to sleep (TASK_IDLE) until the
> + * @condition evaluates to true.
> + * The @condition is checked each time the waitqueue @wq_head is woken up.
> + *
> + * wake_up() has to be called after changing any variable that could
> + * change the result of the wait condition.
> + *
> + */
> +#define wait_event_idle(wq_head, condition)					\
> +do {										\
> +	might_sleep();								\
> +	if (!(condition))							\
> +		___wait_event(wq_head, condition, TASK_IDLE, 0, 0, schedule());	\
> +} while (0)
> +
> +/**
> + * wait_event_idle_exclusive - wait for a condition with contributing to system load
> + * @wq_head: the waitqueue to wait on
> + * @condition: a C expression for the event to wait for
> + *
> + * The process is put to sleep (TASK_IDLE) until the
> + * @condition evaluates to true.
> + * The @condition is checked each time the waitqueue @wq_head is woken up.
> + *
> + * The process is put on the wait queue with an WQ_FLAG_EXCLUSIVE flag
> + * set thus when other process waits process on the list if this
> + * process is awaken further processes are not considered.
> + *
> + * wake_up() has to be called after changing any variable that could
> + * change the result of the wait condition.
> + *
> + */
> +#define wait_event_idle_exclusive(wq_head, condition)				\
> +do {										\
> +	might_sleep();								\
> +	if (!(condition))							\
> +		___wait_event(wq_head, condition, TASK_IDLE, 1, 0, schedule());	\
> +} while (0)
> +
> +#define __wait_event_idle_timeout(wq_head, condition, timeout)			\
> +	___wait_event(wq_head, ___wait_cond_timeout(condition),			\
> +		      TASK_IDLE, 0, timeout,					\
> +		      __ret = schedule_timeout(__ret))
> +
> +/**
> + * wait_event_idle_timeout - sleep without load until a condition gets true or a timeout elapses
> + * @wq_head: the waitqueue to wait on
> + * @condition: a C expression for the event to wait for
> + * @timeout: timeout, in jiffies
> + *
> + * The process is put to sleep (TASK_IDLE) until the
> + * @condition evaluates to true. The @condition is checked each time
> + * the waitqueue @wq_head is woken up.
> + *
> + * wake_up() has to be called after changing any variable that could
> + * change the result of the wait condition.
> + *
> + * Returns:
> + * 0 if the @condition evaluated to %false after the @timeout elapsed,
> + * 1 if the @condition evaluated to %true after the @timeout elapsed,
> + * or the remaining jiffies (at least 1) if the @condition evaluated
> + * to %true before the @timeout elapsed.
> + */
> +#define wait_event_idle_timeout(wq_head, condition, timeout)			\
> +({										\
> +	long __ret = timeout;							\
> +	might_sleep();								\
> +	if (!___wait_cond_timeout(condition))					\
> +		__ret = __wait_event_timeout(wq_head, condition, timeout);	\
> +	__ret;									\
> +})
> +
>  extern int do_wait_intr(wait_queue_head_t *, wait_queue_entry_t *);
>  extern int do_wait_intr_irq(wait_queue_head_t *, wait_queue_entry_t *);
>  
> 
>