Hello Nicholas,
What do you think about this patch?
Thanks,
Andrei
On Wed, Mar 21, 2018 at 11:55:02PM -0700, Andrei Vagin wrote:
> There are two advantages:
> * Direct I/O allows to avoid the write-back cache, so it reduces
> affects to other processes in the system.
> * Async I/O allows to handle a few commands concurrently.
>
> DIO + AIO shows a better perfomance for random write operations:
>
> Mode: O_DSYNC Async: 1
> $ ./fio --bs=4K --direct=1 --rw=randwrite --ioengine=libaio --iodepth=64
> --name=/dev/sda --runtime=20 --numjobs=2
> WRITE: bw=45.9MiB/s (48.1MB/s), 21.9MiB/s-23.0MiB/s (22.0MB/s-25.2MB/s),
> io=919MiB (963MB), run=20002-20020msec
>
> Mode: O_DSYNC Async: 0
> $ ./fio --bs=4K --direct=1 --rw=randwrite --ioengine=libaio --iodepth=64
> --name=/dev/sdb --runtime=20 --numjobs=2
> WRITE: bw=1607KiB/s (1645kB/s), 802KiB/s-805KiB/s (821kB/s-824kB/s),
> io=31.8MiB (33.4MB), run=20280-20295msec
>
> Known issue:
>
> DIF (PI) emulation doesn't work when a target uses async I/O, because
> DIF metadata is saved in a separate file, and it is another non-trivial
> task how to synchronize writing in two files, so that a following read
> operation always returns a consisten metadata for a specified block.
>
> v2: fix comments from Christoph Hellwig
>
> Cc: "Nicholas A. Bellinger" <n...@linux-iscsi.org>
> Cc: Christoph Hellwig <h...@infradead.org>
> Cc: Bryant G. Ly <bryan...@linux.vnet.ibm.com>
> Tested-by: Bryant G. Ly <bryan...@linux.vnet.ibm.com>
> Signed-off-by: Andrei Vagin <ava...@openvz.org>
> ---
> drivers/target/target_core_file.c | 137
> ++++++++++++++++++++++++++++++++++----
> drivers/target/target_core_file.h | 1 +
> 2 files changed, 124 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/target/target_core_file.c
> b/drivers/target/target_core_file.c
> index 9b2c0c773022..16751ae55d7b 100644
> --- a/drivers/target/target_core_file.c
> +++ b/drivers/target/target_core_file.c
> @@ -250,6 +250,84 @@ static void fd_destroy_device(struct se_device *dev)
> }
> }
>
> +struct target_core_file_cmd {
> + unsigned long len;
> + struct se_cmd *cmd;
> + struct kiocb iocb;
> +};
> +
> +static void cmd_rw_aio_complete(struct kiocb *iocb, long ret, long ret2)
> +{
> + struct target_core_file_cmd *cmd;
> +
> + cmd = container_of(iocb, struct target_core_file_cmd, iocb);
> +
> + if (ret != cmd->len)
> + target_complete_cmd(cmd->cmd, SAM_STAT_CHECK_CONDITION);
> + else
> + target_complete_cmd(cmd->cmd, SAM_STAT_GOOD);
> +
> + kfree(cmd);
> +}
> +
> +static sense_reason_t
> +fd_execute_rw_aio(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
> + enum dma_data_direction data_direction)
> +{
> + int is_write = !(data_direction == DMA_FROM_DEVICE);
> + struct se_device *dev = cmd->se_dev;
> + struct fd_dev *fd_dev = FD_DEV(dev);
> + struct file *file = fd_dev->fd_file;
> + struct target_core_file_cmd *aio_cmd;
> + struct iov_iter iter = {};
> + struct scatterlist *sg;
> + struct bio_vec *bvec;
> + ssize_t len = 0;
> + int ret = 0, i;
> +
> + aio_cmd = kmalloc(sizeof(struct target_core_file_cmd), GFP_KERNEL);
> + if (!aio_cmd)
> + return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
> +
> + bvec = kcalloc(sgl_nents, sizeof(struct bio_vec), GFP_KERNEL);
> + if (!bvec) {
> + kfree(aio_cmd);
> + return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
> + }
> +
> + for_each_sg(sgl, sg, sgl_nents, i) {
> + bvec[i].bv_page = sg_page(sg);
> + bvec[i].bv_len = sg->length;
> + bvec[i].bv_offset = sg->offset;
> +
> + len += sg->length;
> + }
> +
> + iov_iter_bvec(&iter, ITER_BVEC | is_write, bvec, sgl_nents, len);
> +
> + aio_cmd->cmd = cmd;
> + aio_cmd->len = len;
> + aio_cmd->iocb.ki_pos = cmd->t_task_lba * dev->dev_attrib.block_size;
> + aio_cmd->iocb.ki_filp = file;
> + aio_cmd->iocb.ki_complete = cmd_rw_aio_complete;
> + aio_cmd->iocb.ki_flags = IOCB_DIRECT;
> +
> + if (is_write && (cmd->se_cmd_flags & SCF_FUA))
> + aio_cmd->iocb.ki_flags |= IOCB_DSYNC;
> +
> + if (is_write)
> + ret = call_write_iter(file, &aio_cmd->iocb, &iter);
> + else
> + ret = call_read_iter(file, &aio_cmd->iocb, &iter);
> +
> + kfree(bvec);
> +
> + if (ret != -EIOCBQUEUED)
> + cmd_rw_aio_complete(&aio_cmd->iocb, ret, 0);
> +
> + return 0;
> +}
> +
> static int fd_do_rw(struct se_cmd *cmd, struct file *fd,
> u32 block_size, struct scatterlist *sgl,
> u32 sgl_nents, u32 data_length, int is_write)
> @@ -527,7 +605,7 @@ fd_execute_unmap(struct se_cmd *cmd, sector_t lba,
> sector_t nolb)
> }
>
> static sense_reason_t
> -fd_execute_rw(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
> +fd_execute_rw_buffered(struct se_cmd *cmd, struct scatterlist *sgl, u32
> sgl_nents,
> enum dma_data_direction data_direction)
> {
> struct se_device *dev = cmd->se_dev;
> @@ -537,16 +615,6 @@ fd_execute_rw(struct se_cmd *cmd, struct scatterlist
> *sgl, u32 sgl_nents,
> sense_reason_t rc;
> int ret = 0;
> /*
> - * We are currently limited by the number of iovecs (2048) per
> - * single vfs_[writev,readv] call.
> - */
> - if (cmd->data_length > FD_MAX_BYTES) {
> - pr_err("FILEIO: Not able to process I/O of %u bytes due to"
> - "FD_MAX_BYTES: %u iovec count limitation\n",
> - cmd->data_length, FD_MAX_BYTES);
> - return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
> - }
> - /*
> * Call vectorized fileio functions to map struct scatterlist
> * physical memory addresses to struct iovec virtual memory.
> */
> @@ -620,14 +688,39 @@ fd_execute_rw(struct se_cmd *cmd, struct scatterlist
> *sgl, u32 sgl_nents,
> return 0;
> }
>
> +static sense_reason_t
> +fd_execute_rw(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
> + enum dma_data_direction data_direction)
> +{
> + struct se_device *dev = cmd->se_dev;
> + struct fd_dev *fd_dev = FD_DEV(dev);
> +
> + /*
> + * We are currently limited by the number of iovecs (2048) per
> + * single vfs_[writev,readv] call.
> + */
> + if (cmd->data_length > FD_MAX_BYTES) {
> + pr_err("FILEIO: Not able to process I/O of %u bytes due to"
> + "FD_MAX_BYTES: %u iovec count limitation\n",
> + cmd->data_length, FD_MAX_BYTES);
> + return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
> + }
> +
> + if (fd_dev->fbd_flags & FDBD_HAS_ASYNC_IO)
> + return fd_execute_rw_aio(cmd, sgl, sgl_nents, data_direction);
> + return fd_execute_rw_buffered(cmd, sgl, sgl_nents, data_direction);
> +}
> +
> enum {
> - Opt_fd_dev_name, Opt_fd_dev_size, Opt_fd_buffered_io, Opt_err
> + Opt_fd_dev_name, Opt_fd_dev_size, Opt_fd_buffered_io,
> + Opt_fd_async_io, Opt_err
> };
>
> static match_table_t tokens = {
> {Opt_fd_dev_name, "fd_dev_name=%s"},
> {Opt_fd_dev_size, "fd_dev_size=%s"},
> {Opt_fd_buffered_io, "fd_buffered_io=%d"},
> + {Opt_fd_async_io, "fd_async_io=%d"},
> {Opt_err, NULL}
> };
>
> @@ -693,6 +786,21 @@ static ssize_t fd_set_configfs_dev_params(struct
> se_device *dev,
>
> fd_dev->fbd_flags |= FDBD_HAS_BUFFERED_IO_WCE;
> break;
> + case Opt_fd_async_io:
> + ret = match_int(args, &arg);
> + if (ret)
> + goto out;
> + if (arg != 1) {
> + pr_err("bogus fd_async_io=%d value\n", arg);
> + ret = -EINVAL;
> + goto out;
> + }
> +
> + pr_debug("FILEIO: Using async I/O"
> + " operations for struct fd_dev\n");
> +
> + fd_dev->fbd_flags |= FDBD_HAS_ASYNC_IO;
> + break;
> default:
> break;
> }
> @@ -709,10 +817,11 @@ static ssize_t fd_show_configfs_dev_params(struct
> se_device *dev, char *b)
> ssize_t bl = 0;
>
> bl = sprintf(b + bl, "TCM FILEIO ID: %u", fd_dev->fd_dev_id);
> - bl += sprintf(b + bl, " File: %s Size: %llu Mode: %s\n",
> + bl += sprintf(b + bl, " File: %s Size: %llu Mode: %s Async:
> %d\n",
> fd_dev->fd_dev_name, fd_dev->fd_dev_size,
> (fd_dev->fbd_flags & FDBD_HAS_BUFFERED_IO_WCE) ?
> - "Buffered-WCE" : "O_DSYNC");
> + "Buffered-WCE" : "O_DSYNC",
> + !!(fd_dev->fbd_flags & FDBD_HAS_ASYNC_IO));
> return bl;
> }
>
> diff --git a/drivers/target/target_core_file.h
> b/drivers/target/target_core_file.h
> index 53be5ffd3261..929b1ecd544e 100644
> --- a/drivers/target/target_core_file.h
> +++ b/drivers/target/target_core_file.h
> @@ -22,6 +22,7 @@
> #define FBDF_HAS_PATH 0x01
> #define FBDF_HAS_SIZE 0x02
> #define FDBD_HAS_BUFFERED_IO_WCE 0x04
> +#define FDBD_HAS_ASYNC_IO 0x08
> #define FDBD_FORMAT_UNIT_SIZE 2048
>
> struct fd_dev {
> --
> 2.13.6
>
