>From 47e523b9ee988317369eaadb96826323cd86819e Mon Sep 17 00:00:00 2001
From: Ming Lei <ming.lei@xxxxxxxxxx>
Date: Wed, 16 Jun 2021 16:13:46 +0800
Subject: [RFC PATCH V3 3/3] dm: support bio polling
Support bio(REQ_POLLED) polling in the following approach:
1) only support io polling on normal READ/WRITE, and other abnormal IOs
still fallback on IRQ mode, so the target io is exactly inside the dm
io.
2) hold one refcnt on io->io_count after submitting this dm bio with
REQ_POLLED
3) support dm native bio splitting, any dm io instance associated with
current bio will be added into one list which head is bio->bi_end_io
which will be recovered before ending this bio
4) implement .poll_bio() callback, call bio_poll() on the single target
bio inside the dm io which is retrieved via bio->bi_bio_drv_data; call
dec_pending() after the target io is done in .poll_bio()
4) enable QUEUE_FLAG_POLL if all underlying queues enable QUEUE_FLAG_POLL,
which is based on Jeffle's previous patch.
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
V3:
- covers all comments from Jeffle
- fix corner cases when polling on abnormal ios
drivers/md/dm-table.c | 24 ++++++++
drivers/md/dm.c | 127 ++++++++++++++++++++++++++++++++++++++++--
2 files changed, 147 insertions(+), 4 deletions(-)
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index ee47a332b462..b14b379442d2 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1491,6 +1491,12 @@ struct dm_target *dm_table_find_target(struct dm_table *t, sector_t sector)
return &t->targets[(KEYS_PER_NODE * n) + k];
}
+static int device_not_poll_capable(struct dm_target *ti, struct dm_dev *dev,
+ sector_t start, sector_t len, void *data)
+{
+ return !blk_queue_poll(bdev_get_queue(dev->bdev));
+}
+
/*
* type->iterate_devices() should be called when the sanity check needs to
* iterate and check all underlying data devices. iterate_devices() will
@@ -1541,6 +1547,11 @@ static int count_device(struct dm_target *ti, struct dm_dev *dev,
return 0;
}
+static int dm_table_supports_poll(struct dm_table *t)
+{
+ return !dm_table_any_dev_attr(t, device_not_poll_capable, NULL);
+}
+
/*
* Check whether a table has no data devices attached using each
* target's iterate_devices method.
@@ -2078,6 +2089,19 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
dm_update_keyslot_manager(q, t);
blk_queue_update_readahead(q);
+
+ /*
+ * Check for request-based device is remained to
+ * dm_mq_init_request_queue()->blk_mq_init_allocated_queue().
+ * For bio-based device, only set QUEUE_FLAG_POLL when all underlying
+ * devices supporting polling.
+ */
+ if (__table_type_bio_based(t->type)) {
+ if (dm_table_supports_poll(t))
+ blk_queue_flag_set(QUEUE_FLAG_POLL, q);
+ else
+ blk_queue_flag_clear(QUEUE_FLAG_POLL, q);
+ }
}
unsigned int dm_table_get_num_targets(struct dm_table *t)
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 363f12a285ce..df4a6a999014 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -39,6 +39,8 @@
#define DM_COOKIE_ENV_VAR_NAME "DM_COOKIE"
#define DM_COOKIE_LENGTH 24
+#define REQ_SAVED_END_IO REQ_DRV
+
static const char *_name = DM_NAME;
static unsigned int major = 0;
@@ -72,6 +74,7 @@ struct clone_info {
struct dm_io *io;
sector_t sector;
unsigned sector_count;
+ bool submit_as_polled;
};
/*
@@ -99,6 +102,8 @@ struct dm_io {
blk_status_t status;
atomic_t io_count;
struct bio *orig_bio;
+ void *saved_bio_end_io;
+ struct hlist_node node;
unsigned long start_time;
spinlock_t endio_lock;
struct dm_stats_aux stats_aux;
@@ -687,6 +692,8 @@ static struct dm_target_io *alloc_tio(struct clone_info *ci, struct dm_target *t
tio->ti = ti;
tio->target_bio_nr = target_bio_nr;
+ WARN_ON_ONCE(ci->submit_as_polled && !tio->inside_dm_io);
+
return tio;
}
@@ -938,8 +945,14 @@ static void dec_pending(struct dm_io *io, blk_status_t error)
end_io_acct(io);
free_io(md, io);
- if (io_error == BLK_STS_DM_REQUEUE)
+ if (io_error == BLK_STS_DM_REQUEUE) {
+ /*
+ * Upper layer won't help us poll split bio, so
+ * clear REQ_POLLED in case of requeue
+ */
+ bio->bi_opf &= ~REQ_POLLED;
return;
+ }
if ((bio->bi_opf & REQ_PREFLUSH) && bio->bi_iter.bi_size) {
/*
@@ -1574,6 +1587,32 @@ static bool __process_abnormal_io(struct clone_info *ci, struct dm_target *ti,
return true;
}
+static void dm_setup_polled_io(struct clone_info *ci)
+{
+ struct bio *bio = ci->bio;
+
+ /*
+ * Only support bio polling for normal IO, and the target io is
+ * exactly inside the dm io instance
+ */
+ ci->submit_as_polled = !!(bio->bi_opf & REQ_POLLED);
+ if (!ci->submit_as_polled)
+ return;
+
+ INIT_HLIST_NODE(&ci->io->node);
+ /*
+ * Save .bi_end_io into dm_io, so that we can reuse .bi_end_io
+ * for storing dm_io list
+ */
+ if (bio->bi_opf & REQ_SAVED_END_IO) {
+ ci->io->saved_bio_end_io = NULL;
+ } else {
+ ci->io->saved_bio_end_io = bio->bi_end_io;
+ INIT_HLIST_HEAD((struct hlist_head *)&bio->bi_end_io);
+ bio->bi_opf |= REQ_SAVED_END_IO;
+ }
+}
+
/*
* Select the correct strategy for processing a non-flush bio.
*/
@@ -1590,6 +1629,8 @@ static int __split_and_process_non_flush(struct clone_info *ci)
if (__process_abnormal_io(ci, ti, &r))
return r;
+ dm_setup_polled_io(ci);
+
len = min_t(sector_t, max_io_len(ti, ci->sector), ci->sector_count);
r = __clone_and_map_data_bio(ci, ti, ci->sector, &len);
@@ -1666,8 +1707,18 @@ static void __split_and_process_bio(struct mapped_device *md,
}
}
- /* drop the extra reference count */
- dec_pending(ci.io, errno_to_blk_status(error));
+ /*
+ * Drop the extra reference count for non-POLLED bio, and hold one
+ * reference for POLLED bio, which will be released in dm_poll_bio
+ *
+ * Add every dm_io instance into the hlist_head which is stored in
+ * bio->bi_end_io, so that dm_poll_bio can poll them all.
+ */
+ if (!ci.submit_as_polled)
+ dec_pending(ci.io, errno_to_blk_status(error));
+ else
+ hlist_add_head(&ci.io->node,
+ (struct hlist_head *)&bio->bi_end_io);
}
static void dm_submit_bio(struct bio *bio)
@@ -1690,8 +1741,11 @@ static void dm_submit_bio(struct bio *bio)
bio_wouldblock_error(bio);
else if (bio->bi_opf & REQ_RAHEAD)
bio_io_error(bio);
- else
+ else {
+ /* Not ready for poll */
+ bio->bi_opf &= ~REQ_POLLED;
queue_io(md, bio);
+ }
goto out;
}
@@ -1707,6 +1761,70 @@ static void dm_submit_bio(struct bio *bio)
dm_put_live_table(md, srcu_idx);
}
+static bool dm_poll_dm_io(struct dm_io *io, unsigned int flags)
+{
+ WARN_ON_ONCE(!io->tio.inside_dm_io);
+
+ bio_poll(&io->tio.clone, flags);
+
+ /* bio_poll holds the last reference */
+ return atomic_read(&io->io_count) == 1;
+}
+
+static int dm_poll_bio(struct bio *bio, unsigned int flags)
+{
+ struct dm_io *io;
+ void *saved_bi_end_io = NULL;
+ struct hlist_head tmp = HLIST_HEAD_INIT;
+ struct hlist_head *head = (struct hlist_head *)&bio->bi_end_io;
+ struct hlist_node *next;
+
+ /*
+ * This bio can be submitted from FS as POLLED so that FS may keep
+ * polling even though the flag is cleared by bio splitting or
+ * requeue, so return immediately.
+ */
+ if (!(bio->bi_opf & REQ_POLLED))
+ return 0;
+
+ /* We only poll normal bio which was marked as REQ_SAVED_END_IO */
+ if (!(bio->bi_opf & REQ_SAVED_END_IO))
+ return 0;
+
+ WARN_ON_ONCE(hlist_empty(head));
+
+ hlist_move_list(head, &tmp);
+
+ hlist_for_each_entry(io, &tmp, node) {
+ if (io->saved_bio_end_io) {
+ saved_bi_end_io = io->saved_bio_end_io;
+ break;
+ }
+ }
+
+ /* restore .bi_end_io before completing dm io */
+ WARN_ON_ONCE(!saved_bi_end_io);
+ bio->bi_opf &= ~REQ_SAVED_END_IO;
+ bio->bi_end_io = saved_bi_end_io;
+
+ hlist_for_each_entry_safe(io, next, &tmp, node) {
+ if (dm_poll_dm_io(io, flags)) {
+ hlist_del_init(&io->node);
+ dec_pending(io, 0);
+ }
+ }
+
+ /* Not done, make sure at least one dm_io stores the .bi_end_io*/
+ if (!hlist_empty(&tmp)) {
+ io = hlist_entry(tmp.first, struct dm_io, node);
+ io->saved_bio_end_io = saved_bi_end_io;
+ bio->bi_opf |= REQ_SAVED_END_IO;
+ hlist_move_list(&tmp, head);
+ return 0;
+ }
+ return 1;
+}
+
/*-----------------------------------------------------------------
* An IDR is used to keep track of allocated minor numbers.
*---------------------------------------------------------------*/
@@ -3121,6 +3239,7 @@ static const struct pr_ops dm_pr_ops = {
static const struct block_device_operations dm_blk_dops = {
.submit_bio = dm_submit_bio,
+ .poll_bio = dm_poll_bio,
.open = dm_blk_open,
.release = dm_blk_close,
.ioctl = dm_blk_ioctl,
--
2.31.1
