From c4cf5261f8bffd9de132b50660a69148e7575bd6 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Fri, 17 Apr 2015 16:15:18 -0600 Subject: [PATCH] bio: skip atomic inc/dec of ->bi_remaining for non-chains Struct bio has an atomic ref count for chained bio's, and we use this to know when to end IO on the bio. However, most bio's are not chained, so we don't need to always introduce this atomic operation as part of ending IO. Add a helper to elevate the bi_remaining count, and flag the bio as now actually needing the decrement at end_io time. Rename the field to __bi_remaining to catch any current users of this doing the incrementing manually. For high IOPS workloads, this reduces the overhead of bio_endio() substantially. Tested-by: Robert Elliott Acked-by: Kent Overstreet Reviewed-by: Jan Kara Signed-off-by: Jens Axboe --- block/bio.c | 38 +++++++++++++++++++++++++++--------- drivers/md/dm-cache-target.c | 2 +- drivers/md/dm-raid1.c | 2 +- drivers/md/dm-snap.c | 2 +- drivers/md/dm-thin.c | 4 ++-- include/linux/bio.h | 11 +++++++++++ include/linux/blk_types.h | 3 ++- 7 files changed, 47 insertions(+), 15 deletions(-) diff --git a/block/bio.c b/block/bio.c index f66a4eae16ee..117da319afb6 100644 --- a/block/bio.c +++ b/block/bio.c @@ -270,7 +270,7 @@ void bio_init(struct bio *bio) { memset(bio, 0, sizeof(*bio)); bio->bi_flags = 1 << BIO_UPTODATE; - atomic_set(&bio->bi_remaining, 1); + atomic_set(&bio->__bi_remaining, 1); atomic_set(&bio->bi_cnt, 1); } EXPORT_SYMBOL(bio_init); @@ -292,8 +292,8 @@ void bio_reset(struct bio *bio) __bio_free(bio); memset(bio, 0, BIO_RESET_BYTES); - bio->bi_flags = flags|(1 << BIO_UPTODATE); - atomic_set(&bio->bi_remaining, 1); + bio->bi_flags = flags | (1 << BIO_UPTODATE); + atomic_set(&bio->__bi_remaining, 1); } EXPORT_SYMBOL(bio_reset); @@ -320,7 +320,7 @@ void bio_chain(struct bio *bio, struct bio *parent) bio->bi_private = parent; bio->bi_end_io = bio_chain_endio; - atomic_inc(&parent->bi_remaining); + bio_inc_remaining(parent); } EXPORT_SYMBOL(bio_chain); @@ -1741,6 +1741,23 @@ void bio_flush_dcache_pages(struct bio *bi) EXPORT_SYMBOL(bio_flush_dcache_pages); #endif +static inline bool bio_remaining_done(struct bio *bio) +{ + /* + * If we're not chaining, then ->__bi_remaining is always 1 and + * we always end io on the first invocation. + */ + if (!bio_flagged(bio, BIO_CHAIN)) + return true; + + BUG_ON(atomic_read(&bio->__bi_remaining) <= 0); + + if (atomic_dec_and_test(&bio->__bi_remaining)) + return true; + + return false; +} + /** * bio_endio - end I/O on a bio * @bio: bio @@ -1758,15 +1775,13 @@ EXPORT_SYMBOL(bio_flush_dcache_pages); void bio_endio(struct bio *bio, int error) { while (bio) { - BUG_ON(atomic_read(&bio->bi_remaining) <= 0); - if (error) clear_bit(BIO_UPTODATE, &bio->bi_flags); else if (!test_bit(BIO_UPTODATE, &bio->bi_flags)) error = -EIO; - if (!atomic_dec_and_test(&bio->bi_remaining)) - return; + if (unlikely(!bio_remaining_done(bio))) + break; /* * Need to have a real endio function for chained bios, @@ -1799,7 +1814,12 @@ EXPORT_SYMBOL(bio_endio); **/ void bio_endio_nodec(struct bio *bio, int error) { - atomic_inc(&bio->bi_remaining); + /* + * If it's not flagged as a chain, we are not going to dec the count + */ + if (bio_flagged(bio, BIO_CHAIN)) + bio_inc_remaining(bio); + bio_endio(bio, error); } EXPORT_SYMBOL(bio_endio_nodec); diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c index 7755af351867..705eb7b99d69 100644 --- a/drivers/md/dm-cache-target.c +++ b/drivers/md/dm-cache-target.c @@ -91,7 +91,7 @@ static void dm_unhook_bio(struct dm_hook_info *h, struct bio *bio) * Must bump bi_remaining to allow bio to complete with * restored bi_end_io. */ - atomic_inc(&bio->bi_remaining); + bio_inc_remaining(bio); } /*----------------------------------------------------------------*/ diff --git a/drivers/md/dm-raid1.c b/drivers/md/dm-raid1.c index 089d62751f7f..d6a1c096b777 100644 --- a/drivers/md/dm-raid1.c +++ b/drivers/md/dm-raid1.c @@ -1254,7 +1254,7 @@ static int mirror_end_io(struct dm_target *ti, struct bio *bio, int error) dm_bio_restore(bd, bio); bio_record->details.bi_bdev = NULL; - atomic_inc(&bio->bi_remaining); + bio_inc_remaining(bio); queue_bio(ms, bio, rw); return DM_ENDIO_INCOMPLETE; diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c index f83a0f3fc365..8bfeae218531 100644 --- a/drivers/md/dm-snap.c +++ b/drivers/md/dm-snap.c @@ -1478,7 +1478,7 @@ out: if (full_bio) { full_bio->bi_end_io = pe->full_bio_end_io; full_bio->bi_private = pe->full_bio_private; - atomic_inc(&full_bio->bi_remaining); + bio_inc_remaining(full_bio); } increment_pending_exceptions_done_count(); diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c index 921aafd12aee..342dbdad6131 100644 --- a/drivers/md/dm-thin.c +++ b/drivers/md/dm-thin.c @@ -795,7 +795,7 @@ static void process_prepared_mapping_fail(struct dm_thin_new_mapping *m) { if (m->bio) { m->bio->bi_end_io = m->saved_bi_end_io; - atomic_inc(&m->bio->bi_remaining); + bio_inc_remaining(m->bio); } cell_error(m->tc->pool, m->cell); list_del(&m->list); @@ -812,7 +812,7 @@ static void process_prepared_mapping(struct dm_thin_new_mapping *m) bio = m->bio; if (bio) { bio->bi_end_io = m->saved_bi_end_io; - atomic_inc(&bio->bi_remaining); + bio_inc_remaining(bio); } if (m->err) { diff --git a/include/linux/bio.h b/include/linux/bio.h index da3a127c9958..8bfe9eee6d1a 100644 --- a/include/linux/bio.h +++ b/include/linux/bio.h @@ -644,6 +644,17 @@ static inline struct bio *bio_list_get(struct bio_list *bl) return bio; } +/* + * Increment chain count for the bio. Make sure the CHAIN flag update + * is visible before the raised count. + */ +static inline void bio_inc_remaining(struct bio *bio) +{ + bio->bi_flags |= (1 << BIO_CHAIN); + smp_mb__before_atomic(); + atomic_inc(&bio->__bi_remaining); +} + /* * bio_set is used to allow other portions of the IO system to * allocate their own private memory pools for bio and iovec structures. diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h index a1b25e35ea5f..8b07e0603887 100644 --- a/include/linux/blk_types.h +++ b/include/linux/blk_types.h @@ -65,7 +65,7 @@ struct bio { unsigned int bi_seg_front_size; unsigned int bi_seg_back_size; - atomic_t bi_remaining; + atomic_t __bi_remaining; bio_end_io_t *bi_end_io; @@ -122,6 +122,7 @@ struct bio { #define BIO_NULL_MAPPED 8 /* contains invalid user pages */ #define BIO_QUIET 9 /* Make BIO Quiet */ #define BIO_SNAP_STABLE 10 /* bio data must be snapshotted during write */ +#define BIO_CHAIN 11 /* chained bio, ->bi_remaining in effect */ /* * Flags starting here get preserved by bio_reset() - this includes