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block: let io_schedule() flush the plug inline

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Linus correctly observes that the most important dispatch cases
are now done from kblockd, this isn't ideal for latency reasons.
The original reason for switching dispatches out-of-line was to
avoid too deep a stack, so by _only_ letting the "accidental"
flush directly in schedule() be guarded by offload to kblockd,
we should be able to get the best of both worlds.

So add a blk_schedule_flush_plug() that offloads to kblockd,
and only use that from the schedule() path.

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
This commit is contained in:
Jens Axboe 2011-04-16 13:27:55 +02:00
parent 5853b4f06f
commit a237c1c5bc
2 changed files with 14 additions and 1 deletions
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13
include/linux/blkdev.h
View File

@ -871,6 +871,14 @@ static inline void blk_flush_plug(struct task_struct *tsk)
{
struct blk_plug *plug = tsk->plug;
if (plug)
blk_flush_plug_list(plug, false);
}
static inline void blk_schedule_flush_plug(struct task_struct *tsk)
{
struct blk_plug *plug = tsk->plug;
if (plug)
blk_flush_plug_list(plug, true);
}
@ -1317,6 +1325,11 @@ static inline void blk_flush_plug(struct task_struct *task)
{
}
static inline void blk_schedule_flush_plug(struct task_struct *task)
{
}
static inline bool blk_needs_flush_plug(struct task_struct *tsk)
{
return false;

2
kernel/sched.c
View File

@ -4118,7 +4118,7 @@ need_resched:
*/
if (blk_needs_flush_plug(prev)) {
raw_spin_unlock(&rq->lock);
blk_flush_plug(prev);
blk_schedule_flush_plug(prev);
raw_spin_lock(&rq->lock);
}
}