[PATCH 4/6] ublk: initialize io_desc on daemon task

[Caleb Sander Mateos <csander@purestorage.com>]

ublk_setup_iod() is currently called to populate struct ublksrv_io_desc
on the thread submitting I/O to a ublk device. However, only the ublk
server threads read the io_descs. This basically guarantees a cache miss
on both threads for each ublk I/O. There's really no need to initialize
the io_descs on the submitting thread. Move the ublk_setup_iod() call to
ublk_dispatch_req() (for non-UBLK_F_BATCH_IO) and
__ublk_batch_prep_dispatch() (for UBLK_F_BATCH_IO), which runs on the
ublk server daemon thread before dispatching the I/O to userspace.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
---
 drivers/block/ublk_drv.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index efbb0d6af128..46f5ab13f87e 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -1786,10 +1786,11 @@ static void ublk_dispatch_req(struct ublk_queue *ubq, struct request *req)
 {
 	unsigned int issue_flags = IO_URING_CMD_TASK_WORK_ISSUE_FLAGS;
 	u16 tag = req->tag;
 	struct ublk_io *io = &ubq->ios[tag];
 
+	ublk_setup_iod(ubq, req);
 	pr_devel("%s: complete: qid %d tag %d io_flags %x addr %llx\n",
 			__func__, ubq->q_id, req->tag, io->flags,
 			ublk_get_iod(ubq, req->tag)->addr);
 
 	/*
@@ -1839,10 +1840,11 @@ static bool __ublk_batch_prep_dispatch(struct ublk_queue *ubq,
 	struct ublk_io *io = &ubq->ios[tag];
 	struct request *req = blk_mq_tag_to_rq(ub->tag_set.tags[ubq->q_id], tag);
 	enum auto_buf_reg_res res = AUTO_BUF_REG_FALLBACK;
 	struct io_uring_cmd *cmd = data->cmd;
 
+	ublk_setup_iod(ubq, req);
 	if (!ublk_start_io(ubq, req, io))
 		return false;
 
 	if (ublk_support_auto_buf_reg(ubq) && blk_rq_has_data(req)) {
 		res = ublk_auto_buf_register(ubq, req, io, cmd,
@@ -2175,11 +2177,10 @@ static blk_status_t ublk_prep_req(struct ublk_queue *ubq, struct request *rq,
 
 	/* fill iod to slot in io cmd buffer */
 	if (unlikely(!ublk_validate_req(ubq, rq)))
 		return BLK_STS_IOERR;
 
-	ublk_setup_iod(ubq, rq);
 	blk_mq_start_request(rq);
 	return BLK_STS_OK;
 }
 
 /*
-- 
2.54.0