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>

diff --git a/drivers/target/target_core_file.c b/drivers/target/target_core_file.c
index 9b2c0c7..16751ae 100644 (file)
--- 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 53be5ff..929b1ec 100644 (file)
--- 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 {