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Subject[PATCH] blk: optimization for classic polling
Date
This removes the dependency on interrupts to wake up task. Set task
state as TASK_RUNNING, if need_resched() returns true,
while polling for IO completion.
Earlier, polling task used to sleep, relying on interrupt to wake it up.
This made some IO take very long when interrupt-coalescing is enabled in
NVMe.

Reference:
http://lists.infradead.org/pipermail/linux-nvme/2018-February/015435.html
Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
---
fs/block_dev.c | 16 ++++++++++++----
fs/direct-io.c | 8 ++++++--
fs/iomap.c | 10 +++++++---
3 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 4a181fc..a87d8b7 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -236,9 +236,13 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter,
set_current_state(TASK_UNINTERRUPTIBLE);
if (!READ_ONCE(bio.bi_private))
break;
- if (!(iocb->ki_flags & IOCB_HIPRI) ||
- !blk_poll(bdev_get_queue(bdev), qc))
+ if (!(iocb->ki_flags & IOCB_HIPRI))
io_schedule();
+ else if (!blk_poll(bdev_get_queue(bdev), qc)) {
+ if (need_resched())
+ set_current_state(TASK_RUNNING);
+ io_schedule();
+ }
}
__set_current_state(TASK_RUNNING);

@@ -401,9 +405,13 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
if (!READ_ONCE(dio->waiter))
break;

- if (!(iocb->ki_flags & IOCB_HIPRI) ||
- !blk_poll(bdev_get_queue(bdev), qc))
+ if (!(iocb->ki_flags & IOCB_HIPRI))
io_schedule();
+ else if (!blk_poll(bdev_get_queue(bdev), qc)) {
+ if (need_resched())
+ set_current_state(TASK_RUNNING);
+ io_schedule();
+ }
}
__set_current_state(TASK_RUNNING);

diff --git a/fs/direct-io.c b/fs/direct-io.c
index a0ca9e4..c815ac9 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -518,9 +518,13 @@ static struct bio *dio_await_one(struct dio *dio)
__set_current_state(TASK_UNINTERRUPTIBLE);
dio->waiter = current;
spin_unlock_irqrestore(&dio->bio_lock, flags);
- if (!(dio->iocb->ki_flags & IOCB_HIPRI) ||
- !blk_poll(dio->bio_disk->queue, dio->bio_cookie))
+ if (!(dio->iocb->ki_flags & IOCB_HIPRI))
io_schedule();
+ else if (!blk_poll(dio->bio_disk->queue, dio->bio_cookie)) {
+ if (need_resched())
+ __set_current_state(TASK_RUNNING);
+ io_schedule();
+ }
/* wake up sets us TASK_RUNNING */
spin_lock_irqsave(&dio->bio_lock, flags);
dio->waiter = NULL;
diff --git a/fs/iomap.c b/fs/iomap.c
index afd1635..b51569d 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -1072,10 +1072,14 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
break;

if (!(iocb->ki_flags & IOCB_HIPRI) ||
- !dio->submit.last_queue ||
- !blk_poll(dio->submit.last_queue,
- dio->submit.cookie))
+ !dio->submit.last_queue)
io_schedule();
+ else if (!blk_poll(dio->submit.last_queue,
+ dio->submit.cookie)) {
+ if (need_resched())
+ set_current_state(TASK_RUNNING);
+ io_schedule();
+ }
}
__set_current_state(TASK_RUNNING);
}
--
2.7.4
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