On Tue, Jul 26, 2022 at 07:44:05PM +0800, ZiyangZhang wrote: > UBLK_IO_NEED_GET_DATA is one ublk IO command. It is designed for a user > application who wants to allocate IO buffer and set IO buffer address > only after it receives an IO request from ublksrv. This is a reasonable > scenario because these users may use a RPC framework as one IO backend > to handle IO requests passed from ublksrv. And a RPC framework may > allocate its own buffer(or memory pool). > > This new feature (UBLK_F_NEED_GET_DATA) is optional for ublk users. > Related userspace code has been added in ublksrv[1] as one pull request. > > Test cases for this feature are added in ublksrv and all the tests pass. > The performance result shows that this new feature does bring additional > latency because one IO is issued back to ublk_drv once again to copy data > from bio vectors to user-provided data buffer. UBLK_IO_NEED_GET_DATA is > suitable for bigger block size such as 512B or 1MB. > > [1] https://github.com/ming1/ubdsrv > > Signed-off-by: ZiyangZhang <ZiyangZhang@xxxxxxxxxxxxxxxxx> > --- > drivers/block/ublk_drv.c | 88 ++++++++++++++++++++++++++++++++++++---- > 1 file changed, 79 insertions(+), 9 deletions(-) > > diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c > index 255b2de46a24..c2d2cd5ab25c 100644 > --- a/drivers/block/ublk_drv.c > +++ b/drivers/block/ublk_drv.c > @@ -47,7 +47,9 @@ > #define UBLK_MINORS (1U << MINORBITS) > > /* All UBLK_F_* have to be included into UBLK_F_ALL */ > -#define UBLK_F_ALL (UBLK_F_SUPPORT_ZERO_COPY | UBLK_F_URING_CMD_COMP_IN_TASK) > +#define UBLK_F_ALL (UBLK_F_SUPPORT_ZERO_COPY \ > + | UBLK_F_URING_CMD_COMP_IN_TASK \ > + | UBLK_F_NEED_GET_DATA) > > struct ublk_rq_data { > struct callback_head work; > @@ -86,6 +88,15 @@ struct ublk_uring_cmd_pdu { > */ > #define UBLK_IO_FLAG_ABORTED 0x04 > > +/* > + * UBLK_IO_FLAG_NEED_GET_DATA is set because IO command requires > + * get data buffer address from ublksrv. > + * > + * Then, bio data could be copied into this data buffer for a WRITE request > + * after the IO command is issued again and UBLK_IO_FLAG_NEED_GET_DATA is unset. > + */ > +#define UBLK_IO_FLAG_NEED_GET_DATA 0x08 > + > struct ublk_io { > /* userspace buffer address from io cmd */ > __u64 addr; > @@ -163,11 +174,19 @@ static struct miscdevice ublk_misc; > static inline bool ublk_can_use_task_work(const struct ublk_queue *ubq) > { > if (IS_BUILTIN(CONFIG_BLK_DEV_UBLK) && > + !(ubq->flags & UBLK_F_NEED_GET_DATA) && > !(ubq->flags & UBLK_F_URING_CMD_COMP_IN_TASK)) > return true; > return false; NEED_GET_DATA isn't related with using task work. That said if use task work return true, you use task work to handle GET_DATA, otherwise use io_uring_cmd_complete_in_task() to handle it, then either we use task work or use io_uring_cmd_complete_in_task, not mix the two. BTW, in my test, it is observed reliably that task work can get better iops. > } > > +static inline bool ublk_need_get_data(const struct ublk_queue *ubq) > +{ > + if (ubq->flags & UBLK_F_NEED_GET_DATA) > + return true; > + return false; > +} > + > static struct ublk_device *ublk_get_device(struct ublk_device *ub) > { > if (kobject_get_unless_zero(&ub->cdev_dev.kobj)) > @@ -509,6 +528,21 @@ static void __ublk_fail_req(struct ublk_io *io, struct request *req) > } > } > > +static void ubq_complete_io_cmd(struct ublk_io *io, int res) > +{ > + /* mark this cmd owned by ublksrv */ > + io->flags |= UBLK_IO_FLAG_OWNED_BY_SRV; > + > + /* > + * clear ACTIVE since we are done with this sqe/cmd slot > + * We can only accept io cmd in case of being not active. > + */ > + io->flags &= ~UBLK_IO_FLAG_ACTIVE; > + > + /* tell ublksrv one io request is coming */ > + io_uring_cmd_done(io->cmd, res, 0); > +} > + > #define UBLK_REQUEUE_DELAY_MS 3 > > static inline void __ublk_rq_task_work(struct request *req) > @@ -531,6 +565,20 @@ static inline void __ublk_rq_task_work(struct request *req) > return; > } > > + if (ublk_need_get_data(ubq) && > + (req_op(req) == REQ_OP_WRITE || > + req_op(req) == REQ_OP_FLUSH) && > + !(io->flags & UBLK_IO_FLAG_NEED_GET_DATA)) { > + > + io->flags |= UBLK_IO_FLAG_NEED_GET_DATA; > + > + pr_devel("%s: ublk_need_get_data. op %d, qid %d tag %d io_flags %x\n", > + __func__, io->cmd->cmd_op, ubq->q_id, req->tag, io->flags); > + > + ubq_complete_io_cmd(io, UBLK_IO_RES_NEED_GET_DATA); > + return; > + } > + > mapped_bytes = ublk_map_io(ubq, req, io); > > /* partially mapped, update io descriptor */ > @@ -553,17 +601,13 @@ static inline void __ublk_rq_task_work(struct request *req) > mapped_bytes >> 9; > } > > - /* mark this cmd owned by ublksrv */ > - io->flags |= UBLK_IO_FLAG_OWNED_BY_SRV; > - > /* > - * clear ACTIVE since we are done with this sqe/cmd slot > - * We can only accept io cmd in case of being not active. > + * Anyway, we have handled UBLK_IO_NEED_GET_DATA for WRITE/FLUSH requests, > + * or we did nothing for other types requests. > */ > - io->flags &= ~UBLK_IO_FLAG_ACTIVE; > + io->flags &= ~UBLK_IO_FLAG_NEED_GET_DATA; > > - /* tell ublksrv one io request is coming */ > - io_uring_cmd_done(io->cmd, UBLK_IO_RES_OK, 0); > + ubq_complete_io_cmd(io, UBLK_IO_RES_OK); > } > > static void ublk_rq_task_work_cb(struct io_uring_cmd *cmd) > @@ -846,6 +890,16 @@ static void ublk_mark_io_ready(struct ublk_device *ub, struct ublk_queue *ubq) > mutex_unlock(&ub->mutex); > } > > +static void ublk_handle_need_get_data(struct ublk_device *ub, int q_id, > + int tag, struct io_uring_cmd *cmd) > +{ > + struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd); > + struct request *req = blk_mq_tag_to_rq(ub->tag_set.tags[q_id], tag); > + > + pdu->req = req; > + io_uring_cmd_complete_in_task(cmd, ublk_rq_task_work_cb); > +} Here you can choose to use task work or io_uring_cmd_complete_in_task() by checking ublk_can_use_task_work(), just like what ublk_queue_rq() does. > + > static int ublk_ch_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags) > { > struct ublksrv_io_cmd *ub_cmd = (struct ublksrv_io_cmd *)cmd->cmd; > @@ -884,6 +938,14 @@ static int ublk_ch_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags) > goto out; > } > > + /* > + * ensure that the user issues UBLK_IO_NEED_GET_DATA > + * iff the driver have set the UBLK_IO_FLAG_NEED_GET_DATA. > + */ > + if ((!!(io->flags & UBLK_IO_FLAG_NEED_GET_DATA)) > + ^ (cmd_op == UBLK_IO_NEED_GET_DATA)) > + goto out; > + > switch (cmd_op) { > case UBLK_IO_FETCH_REQ: > /* UBLK_IO_FETCH_REQ is only allowed before queue is setup */ > @@ -917,6 +979,14 @@ static int ublk_ch_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags) > io->cmd = cmd; > ublk_commit_completion(ub, ub_cmd); > break; > + case UBLK_IO_NEED_GET_DATA: > + if (!(io->flags & UBLK_IO_FLAG_OWNED_BY_SRV)) > + goto out; > + io->addr = ub_cmd->addr; > + io->cmd = cmd; > + io->flags |= UBLK_IO_FLAG_ACTIVE; > + ublk_handle_need_get_data(ub, ub_cmd->q_id, ub_cmd->tag, cmd); You still need to clear UBLK_IO_FLAG_OWNED_BY_SRV here. In future, UBLK_IO_FLAG_OWNED_BY_SRV can be removed actually. Thanks, Ming
