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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: Tejun Heo <tj@kernel.org>
Signed-off-by: Peter 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: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Tejun Heo 2016-10-28 12:58:10 -04:00 committed by Ingo Molnar
parent e33a9bba85
commit 10ab56434f
2 changed files with 31 additions and 10 deletions
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8
include/linux/sched.h
View File

@ -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);

33
kernel/sched/core.c
View File

@ -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.