From 769031c92c8b85bd886f7e064430b7b512c68728 Mon Sep 17 00:00:00 2001 From: Andrei Vagin Date: Wed, 21 Mar 2018 23:55:02 -0700 Subject: 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" Cc: Christoph Hellwig Cc: Bryant G. Ly Tested-by: Bryant G. Ly Signed-off-by: Andrei Vagin Reviewed-by: Christoph Hellwig Reviewed-by: Bryant G. Ly Reviewed-by: Mike Christie Signed-off-by: Martin K. Petersen --- drivers/target/target_core_file.h | 1 + 1 file changed, 1 insertion(+) (limited to 'drivers/target/target_core_file.h') diff --git a/drivers/target/target_core_file.h b/drivers/target/target_core_file.h index 53be5ff..929b1ec 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 { -- cgit v1.1