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scsi: target: target/file: Add support of direct and async I/O 

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.

Cc: "Nicholas A. Bellinger" <nab@linux-iscsi.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Tested-by: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Signed-off-by: Andrei Vagin <avagin@openvz.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Reviewed-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
This commit is contained in:
Andrei Vagin 2018-03-21 23:55:02 -07:00 committed by Martin K. Petersen
parent 97e066184b
commit 769031c92c
2 changed files with 124 additions and 14 deletions
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137
drivers/target/target_core_file.c
View File

@ -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;
@ -536,16 +614,6 @@ fd_execute_rw(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
struct file *pfile = fd_dev->fd_prot_file;
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;
}

1
drivers/target/target_core_file.h
View File

@ -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 {