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769031c92c
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> |
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| .. | ||
| iscsi | ||
| loopback | ||
| sbp | ||
| tcm_fc | ||
| Kconfig | ||
| Makefile | ||
| target_core_alua.c | ||
| target_core_alua.h | ||
| target_core_configfs.c | ||
| target_core_device.c | ||
| target_core_fabric_configfs.c | ||
| target_core_fabric_lib.c | ||
| target_core_file.c | ||
| target_core_file.h | ||
| target_core_hba.c | ||
| target_core_iblock.c | ||
| target_core_iblock.h | ||
| target_core_internal.h | ||
| target_core_pr.c | ||
| target_core_pr.h | ||
| target_core_pscsi.c | ||
| target_core_pscsi.h | ||
| target_core_rd.c | ||
| target_core_rd.h | ||
| target_core_sbc.c | ||
| target_core_spc.c | ||
| target_core_stat.c | ||
| target_core_tmr.c | ||
| target_core_tpg.c | ||
| target_core_transport.c | ||
| target_core_ua.c | ||
| target_core_ua.h | ||
| target_core_user.c | ||
| target_core_xcopy.c | ||
| target_core_xcopy.h | ||