On 1/9/21 1:33 AM, Mike Snitzer wrote:
> On Thu, Jan 07 2021 at 10:24pm -0500,
> JeffleXu <jefflexu@xxxxxxxxxxxxxxxxx> wrote:
>
>>
>>
>> On 1/8/21 5:47 AM, Mike Snitzer wrote:
>>> 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).
>>
>> Yes the hybrid polling is not implemented and thus bypassed for
>> bio-based device currently.
>>
>>>
>>>> +
>>>> +/**
>>>> + * 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);
>>
>> The original code is indeed buggy. For bio-based device, ->iopoll() may
>> not be implemented while QUEUE_FLAG_POLL flag is still set, in which
>> case blk_mq_poll() will be called for this bio-based device.
>
> Yes, here is the patch I created to capture my suggestions. Provided it
> looks good to you, please fold it into patch 3 when you rebase for
> posting a v2 of your patchset:
Thanks, I will merge it into the next version.
Thanks,
Jeffle
>
> From: Mike Snitzer <snitzer@xxxxxxxxxx>
> Date: Thu, 7 Jan 2021 20:45:17 -0500
> Subject: [PATCH] fixup patch 3
>
> ---
> block/blk-core.c | 51 +++++++++++++++++++++-----------------------------
> block/blk-mq.c | 6 ++----
> include/linux/blk-mq.h | 3 ++-
> 3 files changed, 25 insertions(+), 35 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index e6671f6ce1a4..44f62dc0fa9f 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1212,22 +1212,6 @@ int blk_bio_poll(struct request_queue *q, blk_qc_t cookie)
> }
> EXPORT_SYMBOL(blk_bio_poll);
>
> -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;
> -}
> -
> /**
> * blk_poll - poll for IO completions
> * @q: the queue
> @@ -1243,6 +1227,8 @@ static bool blk_poll_hybrid(struct request_queue *q, blk_qc_t cookie)
> int blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin)
> {
> long state;
> + struct blk_mq_hw_ctx *hctx = NULL;
> + struct gendisk *disk = NULL;
>
> if (!blk_qc_t_valid(cookie) ||
> !test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
> @@ -1251,26 +1237,31 @@ int blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin)
> 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;
> + 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);
>
> state = current->state;
> do {
> int ret;
> - struct gendisk *disk = queue_to_disk(q);
>
> - if (disk->fops->iopoll)
> + if (hctx)
> + ret = blk_mq_poll(q, hctx, cookie);
> + else if (disk->fops->iopoll)
> ret = disk->fops->iopoll(q, cookie);
> - else
> - ret = blk_mq_poll(q, cookie);
> +
> if (ret > 0) {
> __set_current_state(TASK_RUNNING);
> return ret;
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index fcb44604f806..90d8dead1da5 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -3826,12 +3826,10 @@ bool blk_mq_poll_hybrid(struct request_queue *q,
> return blk_mq_poll_hybrid_sleep(q, rq);
> }
>
> -int blk_mq_poll(struct request_queue *q, blk_qc_t cookie)
> +int blk_mq_poll(struct request_queue *q,
> + struct blk_mq_hw_ctx *hctx, blk_qc_t cookie)
> {
> int ret;
> - struct blk_mq_hw_ctx *hctx;
> -
> - hctx = q->queue_hw_ctx[blk_qc_t_to_queue_num(cookie)];
>
> hctx->poll_invoked++;
> ret = q->mq_ops->poll(hctx);
> diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
> index 2f3742207df5..b95f2ffa866f 100644
> --- a/include/linux/blk-mq.h
> +++ b/include/linux/blk-mq.h
> @@ -607,7 +607,8 @@ 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);
> +int blk_mq_poll(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);
> void blk_mq_hctx_set_fq_lock_class(struct blk_mq_hw_ctx *hctx,
>
--
Thanks,
Jeffle
