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author | Tejun Heo <tj@kernel.org> | 2009-07-03 22:13:18 (GMT) |
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committer | Tejun Heo <tj@kernel.org> | 2009-07-03 22:13:18 (GMT) |
commit | c43768cbb7655ea5ff782ae250f6e2ef4297cf98 (patch) | |
tree | 3982e41dde3eecaa3739a5d1a8ed18d04bd74f01 /Documentation/device-mapper/dm-queue-length.txt | |
parent | 1a8dd307cc0a2119be4e578c517795464e6dabba (diff) | |
parent | 746a99a5af60ee676afa2ba469ccd1373493c7e7 (diff) | |
download | linux-fsl-qoriq-c43768cbb7655ea5ff782ae250f6e2ef4297cf98.tar.xz |
Merge branch 'master' into for-next
Pull linus#master to merge PER_CPU_DEF_ATTRIBUTES and alpha build fix
changes. As alpha in percpu tree uses 'weak' attribute instead of
inline assembly, there's no need for __used attribute.
Conflicts:
arch/alpha/include/asm/percpu.h
arch/mn10300/kernel/vmlinux.lds.S
include/linux/percpu-defs.h
Diffstat (limited to 'Documentation/device-mapper/dm-queue-length.txt')
-rw-r--r-- | Documentation/device-mapper/dm-queue-length.txt | 39 |
1 files changed, 39 insertions, 0 deletions
diff --git a/Documentation/device-mapper/dm-queue-length.txt b/Documentation/device-mapper/dm-queue-length.txt new file mode 100644 index 0000000..f4db256 --- /dev/null +++ b/Documentation/device-mapper/dm-queue-length.txt @@ -0,0 +1,39 @@ +dm-queue-length +=============== + +dm-queue-length is a path selector module for device-mapper targets, +which selects a path with the least number of in-flight I/Os. +The path selector name is 'queue-length'. + +Table parameters for each path: [<repeat_count>] + <repeat_count>: The number of I/Os to dispatch using the selected + path before switching to the next path. + If not given, internal default is used. To check + the default value, see the activated table. + +Status for each path: <status> <fail-count> <in-flight> + <status>: 'A' if the path is active, 'F' if the path is failed. + <fail-count>: The number of path failures. + <in-flight>: The number of in-flight I/Os on the path. + + +Algorithm +========= + +dm-queue-length increments/decrements 'in-flight' when an I/O is +dispatched/completed respectively. +dm-queue-length selects a path with the minimum 'in-flight'. + + +Examples +======== +In case that 2 paths (sda and sdb) are used with repeat_count == 128. + +# echo "0 10 multipath 0 0 1 1 queue-length 0 2 1 8:0 128 8:16 128" \ + dmsetup create test +# +# dmsetup table +test: 0 10 multipath 0 0 1 1 queue-length 0 2 1 8:0 128 8:16 128 +# +# dmsetup status +test: 0 10 multipath 2 0 0 0 1 1 E 0 2 1 8:0 A 0 0 8:16 A 0 0 |