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

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Date:   Sat, 23 Dec 2017 09:59:19 +1100
From:   NeilBrown <neilb@...e.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Oleg Drokin <oleg.drokin@...el.com>,
        Andreas Dilger <andreas.dilger@...el.com>,
        James Simmons <jsimmons@...radead.org>,
        Patrick Farrell <paf@...y.com>
Subject: Re: [PATCH 1/2] sched/wait: add wait_event_idle() functions.


[removing close lustre-devel list as requested, adding assorted Lustre individuals]

On Fri, Dec 22 2017, Peter Zijlstra wrote:

> 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.

Will do.

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

Thanks,
NeilBrown


>
>> 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 *);
>>  
>> 
>> 

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