[PATCH v2 3/6] block: add iopoll method to support bio-based IO polling

Jeffle Xu
2021-01-26T20:36:49Z

->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@linux.alibaba.com>
Suggested-by: Mike Snitzer <snitzer@redhat.com>
---
block/blk-core.c | 70 +++++++++++++++++++++++++++++++++++++++
block/blk-mq.c | 74 ++++++------------------------------------
include/linux/blk-mq.h | 3 ++
include/linux/blkdev.h | 1 +
4 files changed, 84 insertions(+), 64 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 7663a9b94b80..3d93aaa9a49b 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1132,6 +1132,76 @@ blk_qc_t submit_bio(struct bio *bio)
}
EXPORT_SYMBOL(submit_bio);

+/**
+ * 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;
+ 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))
+ return 0;
+
+ if (current->plug)
+ blk_flush_plug_list(current->plug, false);
+
+ 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;
+
+ if (hctx)
+ ret = blk_mq_poll(q, hctx);
+ 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 f285a9123a8b..d058b9cbdf76 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3801,8 +3801,8 @@ 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;

@@ -3826,72 +3826,18 @@ 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, struct blk_mq_hw_ctx *hctx)
{
- 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)];
-
- /*
- * 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++;
-
- 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);
+ int ret;

- if (current->state == TASK_RUNNING)
- return 1;
- if (ret < 0 || !spin)
- break;
- cpu_relax();
- } while (!need_resched());
+ hctx->poll_invoked++;
+ ret = q->mq_ops->poll(hctx);
+ if (ret > 0)
+ hctx->poll_success++;

- __set_current_state(TASK_RUNNING);
- return 0;
+ return ret;
}
-EXPORT_SYMBOL_GPL(blk_poll);
+EXPORT_SYMBOL(blk_mq_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 d705b174d346..8062a2d046a9 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, struct blk_mq_hw_ctx *hctx);
+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 2a802e011a95..bc540df197cb 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1853,6 +1853,7 @@ 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