The initial idea of using splice for zero copy is from Miklos and Stefan. Now io_uring supports IORING_OP_READ[WRITE]_SPLICE_BUF, and ublk can pass request pages via direct/kernel private pipe to backend io_uring read/write handling code. This zero copy implementation improves sequential IO performance obviously. ublksrv code: https://github.com/ming1/ubdsrv/commits/io_uring_splice_buf So far, only loop/null target supports zero copy: ublk add -t loop -f $file -z ublk add -t none -z Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx> --- drivers/block/ublk_drv.c | 169 ++++++++++++++++++++++++++++++++-- include/uapi/linux/ublk_cmd.h | 31 ++++++- 2 files changed, 193 insertions(+), 7 deletions(-) diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c index e6eceee44366..5ef5f2ccb0d5 100644 --- a/drivers/block/ublk_drv.c +++ b/drivers/block/ublk_drv.c @@ -43,6 +43,8 @@ #include <asm/page.h> #include <linux/task_work.h> #include <linux/namei.h> +#include <linux/pipe_fs_i.h> +#include <linux/splice.h> #include <uapi/linux/ublk_cmd.h> #define UBLK_MINORS (1U << MINORBITS) @@ -154,6 +156,8 @@ struct ublk_device { unsigned long state; int ub_number; + struct srcu_struct srcu; + struct mutex mutex; spinlock_t mm_lock; @@ -537,6 +541,9 @@ static int ublk_map_io(const struct ublk_queue *ubq, const struct request *req, if (req_op(req) != REQ_OP_WRITE && req_op(req) != REQ_OP_FLUSH) return rq_bytes; + if (ubq->flags & UBLK_F_SUPPORT_ZERO_COPY) + return rq_bytes; + if (ublk_rq_has_data(req)) { struct ublk_map_data data = { .ubq = ubq, @@ -558,6 +565,9 @@ static int ublk_unmap_io(const struct ublk_queue *ubq, { const unsigned int rq_bytes = blk_rq_bytes(req); + if (ubq->flags & UBLK_F_SUPPORT_ZERO_COPY) + return rq_bytes; + if (req_op(req) == REQ_OP_READ && ublk_rq_has_data(req)) { struct ublk_map_data data = { .ubq = ubq, @@ -1221,6 +1231,7 @@ static void ublk_stop_dev(struct ublk_device *ub) del_gendisk(ub->ub_disk); ub->dev_info.state = UBLK_S_DEV_DEAD; ub->dev_info.ublksrv_pid = -1; + synchronize_srcu(&ub->srcu); put_disk(ub->ub_disk); ub->ub_disk = NULL; unlock: @@ -1355,13 +1366,155 @@ static int ublk_ch_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags) return -EIOCBQUEUED; } +static void ublk_pipe_buf_release(struct pipe_inode_info *pipe, + struct pipe_buffer *buf) +{ +} + +static const struct pipe_buf_operations ublk_pipe_buf_ops = { + .release = ublk_pipe_buf_release, +}; + +static inline bool ublk_check_splice_rw(const struct request *req, + unsigned int flags) +{ + flags &= (SPLICE_F_KERN_FOR_READ | SPLICE_F_KERN_FOR_WRITE); + + if (req_op(req) == REQ_OP_READ && flags == SPLICE_F_KERN_FOR_READ) + return true; + + if (req_op(req) == REQ_OP_WRITE && flags == SPLICE_F_KERN_FOR_WRITE) + return true; + + return false; +} + +static ssize_t ublk_splice_read(struct file *in, loff_t *ppos, + struct pipe_inode_info *pipe, + size_t len, unsigned int flags) +{ + struct ublk_device *ub = in->private_data; + struct req_iterator rq_iter; + struct bio_vec bv; + struct request *req; + struct ublk_queue *ubq; + u16 tag, q_id; + unsigned int done; + int ret, buf_offset, srcu_idx; + + if (!ub) + return -EPERM; + + /* only support direct pipe and we do need confirm */ + if (pipe != current->splice_pipe || !(flags & + SPLICE_F_KERN_NEED_CONFIRM)) + return -EACCES; + + ret = -EINVAL; + + /* protect request queue & disk removed */ + srcu_idx = srcu_read_lock(&ub->srcu); + + if (ub->dev_info.state == UBLK_S_DEV_DEAD) + goto exit; + + tag = ublk_pos_to_tag(*ppos); + q_id = ublk_pos_to_hwq(*ppos); + buf_offset = ublk_pos_to_buf_offset(*ppos); + + if (q_id >= ub->dev_info.nr_hw_queues) + goto exit; + + ubq = ublk_get_queue(ub, q_id); + if (!ubq) + goto exit; + + if (!(ubq->flags & UBLK_F_SUPPORT_ZERO_COPY)) + goto exit; + + /* + * So far just support splice read buffer from ubq daemon context + * because request may be gone in ->splice_read() if the splice + * is called from other context. + * + * TODO: add request protection and relax the following limit. + */ + if (ubq->ubq_daemon != current) + goto exit; + + if (tag >= ubq->q_depth) + goto exit; + + req = blk_mq_tag_to_rq(ub->tag_set.tags[q_id], tag); + if (!req || !blk_mq_request_started(req)) + goto exit; + + pr_devel("%s: qid %d tag %u offset %x, request bytes %u, len %llu flags %x\n", + __func__, tag, q_id, buf_offset, blk_rq_bytes(req), + (unsigned long long)len, flags); + + if (!ublk_check_splice_rw(req, flags)) + goto exit; + + if (!ublk_rq_has_data(req) || !len) + goto exit; + + if (buf_offset + len > blk_rq_bytes(req)) + goto exit; + + done = ret = 0; + rq_for_each_bvec(bv, req, rq_iter) { + struct pipe_buffer buf = { + .ops = &ublk_pipe_buf_ops, + .flags = 0, + .page = bv.bv_page, + .offset = bv.bv_offset, + .len = bv.bv_len, + }; + + if (buf_offset > 0) { + if (buf_offset >= bv.bv_len) { + buf_offset -= bv.bv_len; + continue; + } else { + buf.offset += buf_offset; + buf.len -= buf_offset; + buf_offset = 0; + } + } + + if (done + buf.len > len) + buf.len = len - done; + done += buf.len; + + ret = add_to_pipe(pipe, &buf); + if (unlikely(ret < 0)) { + done -= buf.len; + break; + } + if (done >= len) + break; + } + + if (done) { + *ppos += done; + ret = done; + + pipe_ack_page_consume(pipe); + } +exit: + srcu_read_unlock(&ub->srcu, srcu_idx); + return ret; +} + static const struct file_operations ublk_ch_fops = { .owner = THIS_MODULE, .open = ublk_ch_open, .release = ublk_ch_release, - .llseek = no_llseek, + .llseek = noop_llseek, .uring_cmd = ublk_ch_uring_cmd, .mmap = ublk_ch_mmap, + .splice_read = ublk_splice_read, }; static void ublk_deinit_queue(struct ublk_device *ub, int q_id) @@ -1472,6 +1625,7 @@ static void ublk_cdev_rel(struct device *dev) ublk_deinit_queues(ub); ublk_free_dev_number(ub); mutex_destroy(&ub->mutex); + cleanup_srcu_struct(&ub->srcu); kfree(ub); } @@ -1600,17 +1754,18 @@ static int ublk_ctrl_start_dev(struct ublk_device *ub, struct io_uring_cmd *cmd) set_bit(GD_SUPPRESS_PART_SCAN, &disk->state); get_device(&ub->cdev_dev); + ub->dev_info.state = UBLK_S_DEV_LIVE; ret = add_disk(disk); if (ret) { /* * Has to drop the reference since ->free_disk won't be * called in case of add_disk failure. */ + ub->dev_info.state = UBLK_S_DEV_DEAD; ublk_put_device(ub); goto out_put_disk; } set_bit(UB_STATE_USED, &ub->state); - ub->dev_info.state = UBLK_S_DEV_LIVE; out_put_disk: if (ret) put_disk(disk); @@ -1718,6 +1873,9 @@ static int ublk_ctrl_add_dev(struct io_uring_cmd *cmd) ub = kzalloc(sizeof(*ub), GFP_KERNEL); if (!ub) goto out_unlock; + ret = init_srcu_struct(&ub->srcu); + if (ret) + goto out_free_ub; mutex_init(&ub->mutex); spin_lock_init(&ub->mm_lock); INIT_WORK(&ub->quiesce_work, ublk_quiesce_work_fn); @@ -1726,7 +1884,7 @@ static int ublk_ctrl_add_dev(struct io_uring_cmd *cmd) ret = ublk_alloc_dev_number(ub, header->dev_id); if (ret < 0) - goto out_free_ub; + goto out_clean_srcu; memcpy(&ub->dev_info, &info, sizeof(info)); @@ -1744,9 +1902,6 @@ static int ublk_ctrl_add_dev(struct io_uring_cmd *cmd) if (!IS_BUILTIN(CONFIG_BLK_DEV_UBLK)) ub->dev_info.flags |= UBLK_F_URING_CMD_COMP_IN_TASK; - /* We are not ready to support zero copy */ - ub->dev_info.flags &= ~UBLK_F_SUPPORT_ZERO_COPY; - ub->dev_info.nr_hw_queues = min_t(unsigned int, ub->dev_info.nr_hw_queues, nr_cpu_ids); ublk_align_max_io_size(ub); @@ -1776,6 +1931,8 @@ static int ublk_ctrl_add_dev(struct io_uring_cmd *cmd) ublk_deinit_queues(ub); out_free_dev_number: ublk_free_dev_number(ub); +out_clean_srcu: + cleanup_srcu_struct(&ub->srcu); out_free_ub: mutex_destroy(&ub->mutex); kfree(ub); diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h index f6238ccc7800..a2f6748ee4ca 100644 --- a/include/uapi/linux/ublk_cmd.h +++ b/include/uapi/linux/ublk_cmd.h @@ -54,7 +54,36 @@ #define UBLKSRV_IO_BUF_OFFSET 0x80000000 /* tag bit is 12bit, so at most 4096 IOs for each queue */ -#define UBLK_MAX_QUEUE_DEPTH 4096 +#define UBLK_TAG_BITS 12 +#define UBLK_MAX_QUEUE_DEPTH (1U << UBLK_TAG_BITS) + +/* used in ->splice_read for supporting zero-copy */ +#define UBLK_BUFS_SIZE_BITS 42 +#define UBLK_BUFS_SIZE_MASK ((1ULL << UBLK_BUFS_SIZE_BITS) - 1) +#define UBLK_BUF_SIZE_BITS (UBLK_BUFS_SIZE_BITS - UBLK_TAG_BITS) +#define UBLK_BUF_MAX_SIZE (1ULL << UBLK_BUF_SIZE_BITS) + +static inline __u16 ublk_pos_to_hwq(__u64 pos) +{ + return pos >> UBLK_BUFS_SIZE_BITS; +} + +static inline __u32 ublk_pos_to_buf_offset(__u64 pos) +{ + return (pos & UBLK_BUFS_SIZE_MASK) & (UBLK_BUF_MAX_SIZE - 1); +} + +static inline __u16 ublk_pos_to_tag(__u64 pos) +{ + return (pos & UBLK_BUFS_SIZE_MASK) >> UBLK_BUF_SIZE_BITS; +} + +/* offset of single buffer, which has to be < UBLK_BUX_MAX_SIZE */ +static inline __u64 ublk_pos(__u16 q_id, __u16 tag, __u32 offset) +{ + return (((__u64)q_id) << UBLK_BUFS_SIZE_BITS) | + ((((__u64)tag) << UBLK_BUF_SIZE_BITS) + offset); +} /* * zero copy requires 4k block size, and can remap ublk driver's io -- 2.31.1
