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Diffstat (limited to 'Documentation/device-mapper/dm-service-time.txt')
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diff --git a/Documentation/device-mapper/dm-service-time.txt b/Documentation/device-mapper/dm-service-time.txt deleted file mode 100644 index fb1d4a0cf122..000000000000 --- a/Documentation/device-mapper/dm-service-time.txt +++ /dev/null @@ -1,91 +0,0 @@ -dm-service-time -=============== - -dm-service-time is a path selector module for device-mapper targets, -which selects a path with the shortest estimated service time for -the incoming I/O. - -The service time for each path is estimated by dividing the total size -of in-flight I/Os on a path with the performance value of the path. -The performance value is a relative throughput value among all paths -in a path-group, and it can be specified as a table argument. - -The path selector name is 'service-time'. - -Table parameters for each path: [<repeat_count> [<relative_throughput>]] - <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. - <relative_throughput>: The relative throughput value of the path - among all paths in the path-group. - The valid range is 0-100. - If not given, minimum value '1' is used. - If '0' is given, the path isn't selected while - other paths having a positive value are available. - -Status for each path: <status> <fail-count> <in-flight-size> \ - <relative_throughput> - <status>: 'A' if the path is active, 'F' if the path is failed. - <fail-count>: The number of path failures. - <in-flight-size>: The size of in-flight I/Os on the path. - <relative_throughput>: The relative throughput value of the path - among all paths in the path-group. - - -Algorithm -========= - -dm-service-time adds the I/O size to 'in-flight-size' when the I/O is -dispatched and subtracts when completed. -Basically, dm-service-time selects a path having minimum service time -which is calculated by: - - ('in-flight-size' + 'size-of-incoming-io') / 'relative_throughput' - -However, some optimizations below are used to reduce the calculation -as much as possible. - - 1. If the paths have the same 'relative_throughput', skip - the division and just compare the 'in-flight-size'. - - 2. If the paths have the same 'in-flight-size', skip the division - and just compare the 'relative_throughput'. - - 3. If some paths have non-zero 'relative_throughput' and others - have zero 'relative_throughput', ignore those paths with zero - 'relative_throughput'. - -If such optimizations can't be applied, calculate service time, and -compare service time. -If calculated service time is equal, the path having maximum -'relative_throughput' may be better. So compare 'relative_throughput' -then. - - -Examples -======== -In case that 2 paths (sda and sdb) are used with repeat_count == 128 -and sda has an average throughput 1GB/s and sdb has 4GB/s, -'relative_throughput' value may be '1' for sda and '4' for sdb. - -# echo "0 10 multipath 0 0 1 1 service-time 0 2 2 8:0 128 1 8:16 128 4" \ - dmsetup create test -# -# dmsetup table -test: 0 10 multipath 0 0 1 1 service-time 0 2 2 8:0 128 1 8:16 128 4 -# -# dmsetup status -test: 0 10 multipath 2 0 0 0 1 1 E 0 2 2 8:0 A 0 0 1 8:16 A 0 0 4 - - -Or '2' for sda and '8' for sdb would be also true. - -# echo "0 10 multipath 0 0 1 1 service-time 0 2 2 8:0 128 2 8:16 128 8" \ - dmsetup create test -# -# dmsetup table -test: 0 10 multipath 0 0 1 1 service-time 0 2 2 8:0 128 2 8:16 128 8 -# -# dmsetup status -test: 0 10 multipath 2 0 0 0 1 1 E 0 2 2 8:0 A 0 0 2 8:16 A 0 0 8 |