[tip:sched/core] sched/core: Separate out io_schedule_prepare() and io_schedule_finish()

tip-bot for Tejun Heo
2017-01-14T12:50:36Z

Commit-ID: 10ab56434f2f633a51e432ee8b7c29e12438e163
Gitweb: http://git.kernel.org/tip/10ab56434f2f633a51e432ee8b7c29e12438e163
Author: Tejun Heo <tj@kernel.org>
AuthorDate: Fri, 28 Oct 2016 12:58:10 -0400
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Sat, 14 Jan 2017 11:30:04 +0100

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>
---
include/linux/sched.h | 8 +++-----
kernel/sched/core.c | 33 ++++++++++++++++++++++++++++-----
2 files changed, 31 insertions(+), 10 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 94a48bb..a8daed9 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -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);

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9fd3716..49ce1cb 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5128,25 +5128,48 @@ out_irq:
}
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.