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Commit 10ab5643 authored by Tejun Heo's avatar Tejun Heo Committed by Ingo Molnar
Browse files

sched/core: Separate out io_schedule_prepare() and io_schedule_finish() 



Now that IO schedule accounting is done inside __schedule(),
io_schedule() can be split into three steps - prep, schedule, and
finish - where the schedule part doesn't need any special annotation.
This allows marking a sleep as iowait by simply wrapping an existing
blocking function with io_schedule_prepare() and io_schedule_finish().

Because task_struct->in_iowait is single bit, the caller of
io_schedule_prepare() needs to record and the pass its state to
io_schedule_finish() to be safe regarding nesting.  While this isn't
the prettiest, these functions are mostly gonna be used by core
functions and we don't want to use more space for ->in_iowait.

While at it, as it's simple to do now, reimplement io_schedule()
without unnecessarily going through io_schedule_timeout().

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: adilger.kernel@dilger.ca
Cc: jack@suse.com
Cc: kernel-team@fb.com
Cc: mingbo@fb.com
Cc: tytso@mit.edu
Link: http://lkml.kernel.org/r/1477673892-28940-3-git-send-email-tj@kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent e33a9bba

include/linux/sched.h

+3 −5
Original line number Diff line number Diff line
@@ -461,12 +461,10 @@ extern signed long schedule_timeout_idle(signed long timeout); 
asmlinkage void schedule(void);

extern void schedule_preempt_disabled(void);



extern int __must_check io_schedule_prepare(void);

extern void io_schedule_finish(int token);

extern long io_schedule_timeout(long timeout);



static inline void io_schedule(void)

{

	io_schedule_timeout(MAX_SCHEDULE_TIMEOUT);

}

extern void io_schedule(void);



void __noreturn do_task_dead(void);

kernel/sched/core.c

+28 −5
Original line number Diff line number Diff line
@@ -5128,25 +5128,48 @@ int __sched yield_to(struct task_struct *p, bool preempt) 
}

EXPORT_SYMBOL_GPL(yield_to);



int io_schedule_prepare(void)

{

	int old_iowait = current->in_iowait;



	current->in_iowait = 1;

	blk_schedule_flush_plug(current);



	return old_iowait;

}



void io_schedule_finish(int token)

{

	current->in_iowait = token;

}



/*

 * This task is about to go to sleep on IO. Increment rq->nr_iowait so

 * that process accounting knows that this is a task in IO wait state.

 */

long __sched io_schedule_timeout(long timeout)

{

	int old_iowait = current->in_iowait;

	int token;

	long ret;



	current->in_iowait = 1;

	blk_schedule_flush_plug(current);



	token = io_schedule_prepare();

	ret = schedule_timeout(timeout);

	current->in_iowait = old_iowait;

	io_schedule_finish(token);



	return ret;

}

EXPORT_SYMBOL(io_schedule_timeout);



void io_schedule(void)

{

	int token;



	token = io_schedule_prepare();

	schedule();

	io_schedule_finish(token);

}

EXPORT_SYMBOL(io_schedule);



/**

 * sys_sched_get_priority_max - return maximum RT priority.

 * @policy: scheduling class.