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block: avoid extra iter advance with async iocb 

Nobody cares about iov iterators state if we return -EIOCBQUEUED, so as
the we now have __blkdev_direct_IO_async(), which gets pages only once,
we can skip expensive iov_iter_advance(). It's around 1-2% of all CPU
spent.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/a6158edfbfa2ae3bc24aed29a72f035df18fad2f.1635337135.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2021-10-27 13:21:07 +01:00 committed by Jens Axboe
parent a2247f19ee
commit 1bb6b81029
3 changed files with 17 additions and 6 deletions
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2
block/bio.c
View File

@ -1046,7 +1046,7 @@ void __bio_release_pages(struct bio *bio, bool mark_dirty)
}
EXPORT_SYMBOL_GPL(__bio_release_pages);
static void bio_iov_bvec_set(struct bio *bio, struct iov_iter *iter)
void bio_iov_bvec_set(struct bio *bio, struct iov_iter *iter)
{
size_t size = iov_iter_count(iter);

20
block/fops.c
View File

@ -352,11 +352,21 @@ static ssize_t __blkdev_direct_IO_async(struct kiocb *iocb,
bio->bi_end_io = blkdev_bio_end_io_async;
bio->bi_ioprio = iocb->ki_ioprio;
ret = bio_iov_iter_get_pages(bio, iter);
if (unlikely(ret)) {
bio->bi_status = BLK_STS_IOERR;
bio_endio(bio);
return ret;
if (iov_iter_is_bvec(iter)) {
/*
* Users don't rely on the iterator being in any particular
* state for async I/O returning -EIOCBQUEUED, hence we can
* avoid expensive iov_iter_advance(). Bypass
* bio_iov_iter_get_pages() and set the bvec directly.
*/
bio_iov_bvec_set(bio, iter);
} else {
ret = bio_iov_iter_get_pages(bio, iter);
if (unlikely(ret)) {
bio->bi_status = BLK_STS_IOERR;
bio_endio(bio);
return ret;
}
}
dio->size = bio->bi_iter.bi_size;

1
include/linux/bio.h
View File

@ -417,6 +417,7 @@ int bio_add_zone_append_page(struct bio *bio, struct page *page,
void __bio_add_page(struct bio *bio, struct page *page,
unsigned int len, unsigned int off);
int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter);
void bio_iov_bvec_set(struct bio *bio, struct iov_iter *iter);
void __bio_release_pages(struct bio *bio, bool mark_dirty);
extern void bio_set_pages_dirty(struct bio *bio);
extern void bio_check_pages_dirty(struct bio *bio);