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" <nab@xxxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Bryant G. Ly <bryantly@xxxxxxxxxxxxxxxxxx>
Tested-by: Bryant G. Ly <bryantly@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrei Vagin <avagin@xxxxxxxxxx>
---
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
