On 6/17/21 6:35 PM, Ming Lei wrote: > 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> > --- > drivers/md/dm-table.c | 24 +++++++++ > drivers/md/dm.c | 111 ++++++++++++++++++++++++++++++++++++++++-- > 2 files changed, 132 insertions(+), 3 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..9745c3deacc3 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; > @@ -97,8 +99,11 @@ struct dm_io { > unsigned magic; > struct mapped_device *md; > blk_status_t status; > + bool submit_as_polled; > 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->io->submit_as_polled && !tio->inside_dm_io); > + > return tio; > } > > @@ -938,8 +945,12 @@ 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) { > + /* not poll any more in case of requeue */ > + if (bio->bi_opf & REQ_POLLED) > + bio->bi_opf &= ~REQ_POLLED; > return; > + } Actually I'm not sure why REQ_POLLED should be cleared here. Besides, there's one corner case where bio is submitted when dm device is suspended. ``` static blk_qc_t dm_submit_bio(struct bio *bio) /* If suspended, queue this IO for later */ if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags))) { if (bio->bi_opf & REQ_NOWAIT) bio_wouldblock_error(bio); else if (bio->bi_opf & REQ_RAHEAD) bio_io_error(bio); else queue_io(md, bio); goto out; } ``` When the dm device is suspended with DMF_BLOCK_IO_FOR_SUSPEND, the submitted bio is inserted into @md->deferred list by calling queue_io(). Then the following bio_poll() calling will trigger the 'WARN_ON_ONCE(!saved_bi_end_io)' in dm_poll_bio(), if the previously submitted bio is still buffered in @md->deferred list. ``` submit_bio() dm_submit_bio queue_io bio_poll dm_poll_bio ``` > > if ((bio->bi_opf & REQ_PREFLUSH) && bio->bi_iter.bi_size) { > /* > @@ -1590,6 +1601,12 @@ static int __split_and_process_non_flush(struct clone_info *ci) > if (__process_abnormal_io(ci, ti, &r)) > return r; > > + /* > + * Only support bio polling for normal IO, and the target io is > + * exactly inside the dm io instance > + */ > + ci->io->submit_as_polled = !!(ci->bio->bi_opf & REQ_POLLED); > + > 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); > @@ -1608,6 +1625,22 @@ static void init_clone_info(struct clone_info *ci, struct mapped_device *md, > ci->map = map; > ci->io = alloc_io(md, bio); > ci->sector = bio->bi_iter.bi_sector; > + > + if (bio->bi_opf & REQ_POLLED) { > + 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; > + } > + } > } > > #define __dm_part_stat_sub(part, field, subnd) \ > @@ -1666,8 +1699,19 @@ 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.io->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) > @@ -1707,6 +1751,66 @@ static void dm_submit_bio(struct bio *bio) > dm_put_live_table(md, srcu_idx); > } > > +static int dm_poll_dm_io(struct dm_io *io, unsigned int flags) > +{ > + if (!io || !io->submit_as_polled) > + return 0; Wondering if '!io->submit_as_polled' is necessary here. dm_io will be added into the hash list only when 'io->submit_as_polled' is true in __split_and_process_bio. > + > + WARN_ON_ONCE(!io->tio.inside_dm_io); > + bio_poll(&io->tio.clone, flags); > + > + /* bio_poll holds the last reference */ > + if (atomic_read(&io->io_count) == 1) > + return 1; > + return 0; > +} > + > +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; > + > + hlist_move_list(head, &tmp); > + > + hlist_for_each_entry(io, &tmp, node) { > + if (io->saved_bio_end_io && !saved_bi_end_io) { Seems that checking if saved_bi_end_io NULL here is not necessary, since you will exit thte loop once saved_bi_end_io is assigned. > + 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); Abnormal bio flagged with REQ_POLLED (is this possible?) can still be called with dm_poll_bio(), and will trigger this warning. > + 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; > + hlist_move_list(&tmp, head); > + return 0;> + } > + return 1; > +} > + > /*----------------------------------------------------------------- > * An IDR is used to keep track of allocated minor numbers. > *---------------------------------------------------------------*/ > @@ -3121,6 +3225,7 @@ 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, > -- Thanks, Jeffle -- dm-devel mailing list dm-devel@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/dm-devel