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:
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,
--
2.15.0
