linux-kernel - Re: [PATCH] sched: Introduce TASK_NOLOAD and TASK

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Date:	Mon, 11 May 2015 22:34:11 +0300 (EEST)
From:	Julian Anastasov <ja@....bg>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
	neilb@...e.de
Subject: Re: [PATCH] sched: Introduce TASK_NOLOAD and TASK_IDLE


	Hello,

On Mon, 11 May 2015, Peter Zijlstra wrote:

> > - schedule_timeout_idle (instead of schedule_timeout call):
> > 	__set_current_state(TASK_IDLE);
> > 	return schedule_timeout(timeout);
> > 
> > 	- we here are really idle, so "N" looks ok
> 
> So I don't get the point of the schedule_timeout_*() stubs. What are
> they for? Why would one use an unconditional schedule_timeout() call?
> Isn't that what msleep() is for?

	msleep will not return until timeout has expired.
Instead, we want to notice the kthread_should_stop() event
immediately. Additionally, TASK_UNINTERRUPTIBLE will increase
the load average. We can do it with extra wait queue
and the new __wait_event_idle_timeout but I guess
schedule_timeout_idle will be a good replacement for
schedule_timeout_interruptible calls when used for kthreads.

> + * like wait_event_timeout() -- except it uses TASK_IDLE to avoid loadavg
> + */
> +#define wait_event_idle_timeout(wq, condition, timeout)			\
> +({									\
> +	long __ret = timeout;						\
> +	might_sleep();							\
> +	if (!___wait_cond_timeout(condition))				\
> +		ret = __wait_event_idle_timeout(wq, condition, timeout);\

	ret may need underscores here...

Regards

--
Julian Anastasov <ja@....bg>
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