On Wed, Dec 23 2020 at 6:26am -0500,
Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx> wrote:
> ->poll_fn is introduced in commit ea435e1b9392 ("block: add a poll_fn
> callback to struct request_queue") for supporting non-mq queues such as
> nvme multipath, but removed in commit 529262d56dbe ("block: remove
> ->poll_fn").
>
> To add support of IO polling for non-mq device, this method need to be
> back. Since commit c62b37d96b6e ("block: move ->make_request_fn to
> struct block_device_operations") has moved all callbacks into struct
> block_device_operations in gendisk, we also add the new method named
> ->iopoll in block_device_operations.
Please update patch subject and header to:
block: add iopoll method to support bio-based IO polling
->poll_fn was introduced in commit ea435e1b9392 ("block: add a poll_fn
callback to struct request_queue") to support bio-based queues such as
nvme multipath, but was later removed in commit 529262d56dbe ("block:
remove ->poll_fn").
Given commit c62b37d96b6e ("block: move ->make_request_fn to struct
block_device_operations") restore the possibility of bio-based IO
polling support by adding an ->iopoll method to gendisk->fops.
Elevate bulk of blk_mq_poll() implementation to blk_poll() and reduce
blk_mq_poll() to blk-mq specific code that is called from blk_poll().
> Signed-off-by: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx>
> ---
> block/blk-core.c | 79 ++++++++++++++++++++++++++++++++++++++++++
> block/blk-mq.c | 70 +++++--------------------------------
> include/linux/blk-mq.h | 3 ++
> include/linux/blkdev.h | 1 +
> 4 files changed, 92 insertions(+), 61 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 96e5fcd7f071..2f5c51ce32e3 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1131,6 +1131,85 @@ blk_qc_t submit_bio(struct bio *bio)
> }
> EXPORT_SYMBOL(submit_bio);
>
> +static bool blk_poll_hybrid(struct request_queue *q, blk_qc_t cookie)
> +{
> + struct blk_mq_hw_ctx *hctx;
> +
> + /* TODO: bio-based device doesn't support hybrid poll. */
> + if (!queue_is_mq(q))
> + return false;
> +
> + hctx = q->queue_hw_ctx[blk_qc_t_to_queue_num(cookie)];
> + if (blk_mq_poll_hybrid(q, hctx, cookie))
> + return true;
> +
> + hctx->poll_considered++;
> + return false;
> +}
I don't see where you ever backfill bio-based hybrid support (in
the following patches in this series, so it is lingering TODO).
> +
> +/**
> + * blk_poll - poll for IO completions
> + * @q: the queue
> + * @cookie: cookie passed back at IO submission time
> + * @spin: whether to spin for completions
> + *
> + * Description:
> + * Poll for completions on the passed in queue. Returns number of
> + * completed entries found. If @spin is true, then blk_poll will continue
> + * looping until at least one completion is found, unless the task is
> + * otherwise marked running (or we need to reschedule).
> + */
> +int blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin)
> +{
> + long state;
> +
> + if (!blk_qc_t_valid(cookie) ||
> + !test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
> + return 0;
> +
> + if (current->plug)
> + blk_flush_plug_list(current->plug, false);
> +
> + /*
> + * If we sleep, have the caller restart the poll loop to reset
> + * the state. Like for the other success return cases, the
> + * caller is responsible for checking if the IO completed. If
> + * the IO isn't complete, we'll get called again and will go
> + * straight to the busy poll loop. If specified not to spin,
> + * we also should not sleep.
> + */
> + if (spin && blk_poll_hybrid(q, cookie))
> + return 1;
> +
> + state = current->state;
> + do {
> + int ret;
> + struct gendisk *disk = queue_to_disk(q);
> +
> + if (disk->fops->iopoll)
> + ret = disk->fops->iopoll(q, cookie);
> + else
> + ret = blk_mq_poll(q, cookie);
Really don't like that blk-mq is needlessly getting gendisk and checking
disk->fops->iopoll.
This is just to give an idea, whitespace damaged due to coding in mail
client, but why not remove above blk_poll_hybrid() and do:
struct blk_mq_hw_ctx *hctx = NULL;
struct gendisk *disk = NULL;
...
if (queue_is_mq(q)) {
/*
* If we sleep, have the caller restart the poll loop to reset
* the state. Like for the other success return cases, the
* caller is responsible for checking if the IO completed. If
* the IO isn't complete, we'll get called again and will go
* straight to the busy poll loop. If specified not to spin,
* we also should not sleep.
*/
hctx = q->queue_hw_ctx[blk_qc_t_to_queue_num(cookie)];
if (spin && blk_mq_poll_hybrid(q, hctx, cookie))
return 1;
hctx->poll_considered++;
} else {
disk = queue_to_disk(q);
}
do {
int ret;
if (hctx)
ret = blk_mq_poll(q, hctx, cookie);
else if (disk->fops->iopoll)
ret = disk->fops->iopoll(q, cookie);
> + if (ret > 0) {
> + __set_current_state(TASK_RUNNING);
> + return ret;
> + }
> +
> + if (signal_pending_state(state, current))
> + __set_current_state(TASK_RUNNING);
> +
> + if (current->state == TASK_RUNNING)
> + return 1;
> + if (ret < 0 || !spin)
> + break;
> + cpu_relax();
> + } while (!need_resched());
> +
> + __set_current_state(TASK_RUNNING);
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(blk_poll);
> +
> /**
> * blk_cloned_rq_check_limits - Helper function to check a cloned request
> * for the new queue limits
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index b09ce00cc6af..85258958e9f1 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -3818,8 +3818,8 @@ static bool blk_mq_poll_hybrid_sleep(struct request_queue *q,
> return true;
> }
>
> -static bool blk_mq_poll_hybrid(struct request_queue *q,
> - struct blk_mq_hw_ctx *hctx, blk_qc_t cookie)
> +bool blk_mq_poll_hybrid(struct request_queue *q,
> + struct blk_mq_hw_ctx *hctx, blk_qc_t cookie)
> {
> struct request *rq;
>
> @@ -3843,72 +3843,20 @@ static bool blk_mq_poll_hybrid(struct request_queue *q,
> return blk_mq_poll_hybrid_sleep(q, rq);
> }
>
> -/**
> - * blk_poll - poll for IO completions
> - * @q: the queue
> - * @cookie: cookie passed back at IO submission time
> - * @spin: whether to spin for completions
> - *
> - * Description:
> - * Poll for completions on the passed in queue. Returns number of
> - * completed entries found. If @spin is true, then blk_poll will continue
> - * looping until at least one completion is found, unless the task is
> - * otherwise marked running (or we need to reschedule).
> - */
> -int blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin)
> +int blk_mq_poll(struct request_queue *q, blk_qc_t cookie)
> {
> + int ret;
> struct blk_mq_hw_ctx *hctx;
> - long state;
> -
> - if (!blk_qc_t_valid(cookie) ||
> - !test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
> - return 0;
> -
> - if (current->plug)
> - blk_flush_plug_list(current->plug, false);
>
> hctx = q->queue_hw_ctx[blk_qc_t_to_queue_num(cookie)];
Given my suggested code changes above, pass hctx in to blk_mq_poll() to
avoid redundant code to access it in q->queue_hw_ctx[], so:
int blk_mq_poll(struct request_queue *q,
struct blk_mq_hw_ctx *hctx, blk_qc_t cookie)
> - /*
> - * If we sleep, have the caller restart the poll loop to reset
> - * the state. Like for the other success return cases, the
> - * caller is responsible for checking if the IO completed. If
> - * the IO isn't complete, we'll get called again and will go
> - * straight to the busy poll loop. If specified not to spin,
> - * we also should not sleep.
> - */
> - if (spin && blk_mq_poll_hybrid(q, hctx, cookie))
> - return 1;
> -
> - hctx->poll_considered++;
> + hctx->poll_invoked++;
> + ret = q->mq_ops->poll(hctx);
> + if (ret > 0)
> + hctx->poll_success++;
>
> - state = current->state;
> - do {
> - int ret;
> -
> - hctx->poll_invoked++;
> -
> - ret = q->mq_ops->poll(hctx);
> - if (ret > 0) {
> - hctx->poll_success++;
> - __set_current_state(TASK_RUNNING);
> - return ret;
> - }
> -
> - if (signal_pending_state(state, current))
> - __set_current_state(TASK_RUNNING);
> -
> - if (current->state == TASK_RUNNING)
> - return 1;
> - if (ret < 0 || !spin)
> - break;
> - cpu_relax();
> - } while (!need_resched());
> -
> - __set_current_state(TASK_RUNNING);
> - return 0;
> + return ret;
> }
> -EXPORT_SYMBOL_GPL(blk_poll);
>
> unsigned int blk_mq_rq_cpu(struct request *rq)
> {
> diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
> index 47b021952ac7..032e08ecd42e 100644
> --- a/include/linux/blk-mq.h
> +++ b/include/linux/blk-mq.h
> @@ -607,6 +607,9 @@ static inline void blk_rq_bio_prep(struct request *rq, struct bio *bio,
> }
>
> blk_qc_t blk_mq_submit_bio(struct bio *bio);
> +int blk_mq_poll(struct request_queue *q, blk_qc_t cookie);
> +bool blk_mq_poll_hybrid(struct request_queue *q,
> + struct blk_mq_hw_ctx *hctx, blk_qc_t cookie);
> void blk_mq_hctx_set_fq_lock_class(struct blk_mq_hw_ctx *hctx,
> struct lock_class_key *key);
>
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 2303d06a5a82..e8965879eb90 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -1845,6 +1845,7 @@ static inline void blk_ksm_unregister(struct request_queue *q) { }
>
> struct block_device_operations {
> blk_qc_t (*submit_bio) (struct bio *bio);
> + int (*iopoll)(struct request_queue *q, blk_qc_t cookie);
> int (*open) (struct block_device *, fmode_t);
> void (*release) (struct gendisk *, fmode_t);
> int (*rw_page)(struct block_device *, sector_t, struct page *, unsigned int);
> --
> 2.27.0
>
> --
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