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| author |   Kiyoshi Ueda <k-ueda@ct.jp.nec.com> | 2009-06-22 10:12:27 +0100 |
|---|---|---|
| committer |   Alasdair G Kergon <agk@redhat.com> | 2009-06-22 10:12:27 +0100 |
| commit | fd5e033908b7b743b5650790f196761dd930f988 (patch) | |
| tree | cd264d11371b9410e98388e00f4d87459a5e6325 /Documentation/device-mapper | |
| parent | dm mpath: add start_io and nr_bytes to path selectors (diff) | |
| download | linux-dev-fd5e033908b7b743b5650790f196761dd930f988.tar.xz linux-dev-fd5e033908b7b743b5650790f196761dd930f988.zip | |
dm mpath: add queue length load balancer
This patch adds a dynamic load balancer, dm-queue-length, which
balances the number of in-flight I/Os across the paths.
The code is based on the patch posted by Stefan Bader:
https://www.redhat.com/archives/dm-devel/2005-October/msg00050.html
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Diffstat (limited to 'Documentation/device-mapper')
| -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 000000000000..f4db2562175c --- /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 |