linux/drivers/target/target_core_file.h
Andrei Vagin 769031c92c 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>
2018-05-14 22:40:08 -04:00

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1.2 KiB
C

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef TARGET_CORE_FILE_H
#define TARGET_CORE_FILE_H
#include <target/target_core_base.h>
#define FD_VERSION "4.0"
#define FD_MAX_DEV_NAME 256
#define FD_MAX_DEV_PROT_NAME FD_MAX_DEV_NAME + 16
#define FD_DEVICE_QUEUE_DEPTH 32
#define FD_MAX_DEVICE_QUEUE_DEPTH 128
#define FD_BLOCKSIZE 512
/*
* Limited by the number of iovecs (2048) per vfs_[writev,readv] call
*/
#define FD_MAX_BYTES 8388608
#define RRF_EMULATE_CDB 0x01
#define RRF_GOT_LBA 0x02
#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 {
struct se_device dev;
u32 fbd_flags;
unsigned char fd_dev_name[FD_MAX_DEV_NAME];
/* Unique Ramdisk Device ID in Ramdisk HBA */
u32 fd_dev_id;
/* Number of SG tables in sg_table_array */
u32 fd_table_count;
u32 fd_queue_depth;
u32 fd_block_size;
unsigned long long fd_dev_size;
struct file *fd_file;
struct file *fd_prot_file;
/* FILEIO HBA device is connected to */
struct fd_host *fd_host;
} ____cacheline_aligned;
struct fd_host {
u32 fd_host_dev_id_count;
/* Unique FILEIO Host ID */
u32 fd_host_id;
} ____cacheline_aligned;
#endif /* TARGET_CORE_FILE_H */