diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/device-mapper/statistics.txt | 28 |
1 files changed, 24 insertions, 4 deletions
diff --git a/Documentation/device-mapper/statistics.txt b/Documentation/device-mapper/statistics.txt index 2a1673a..ff6baea 100644 --- a/Documentation/device-mapper/statistics.txt +++ b/Documentation/device-mapper/statistics.txt @@ -13,9 +13,13 @@ the range specified. The I/O statistics counters for each step-sized area of a region are in the same format as /sys/block/*/stat or /proc/diskstats (see: Documentation/iostats.txt). But two extra counters (12 and 13) are -provided: total time spent reading and writing in milliseconds. All -these counters may be accessed by sending the @stats_print message to -the appropriate DM device via dmsetup. +provided: total time spent reading and writing. All these counters may +be accessed by sending the @stats_print message to the appropriate DM +device via dmsetup. + +The reported times are in milliseconds and the granularity depends on +the kernel ticks. When the option precise_timestamps is used, the +reported times are in nanoseconds. Each region has a corresponding unique identifier, which we call a region_id, that is assigned when the region is created. The region_id @@ -33,7 +37,9 @@ memory is used by reading Messages ======== - @stats_create <range> <step> [<program_id> [<aux_data>]] + @stats_create <range> <step> + [<number_of_optional_arguments> <optional_arguments>...] + [<program_id> [<aux_data>]] Create a new region and return the region_id. @@ -48,6 +54,17 @@ Messages "/<number_of_areas>" - the range is subdivided into the specified number of areas. + <number_of_optional_arguments> + The number of optional arguments + + <optional_arguments> + The following optional arguments are supported + precise_timestamps - use precise timer with nanosecond resolution + instead of the "jiffies" variable. When this argument is + used, the resulting times are in nanoseconds instead of + milliseconds. Precise timestamps are a little bit slower + to obtain than jiffies-based timestamps. + <program_id> An optional parameter. A name that uniquely identifies the userspace owner of the range. This groups ranges together @@ -55,6 +72,9 @@ Messages created and ignore those created by others. The kernel returns this string back in the output of @stats_list message, but it doesn't use it for anything else. + If we omit the number of optional arguments, program id must not + be a number, otherwise it would be interpreted as the number of + optional arguments. <aux_data> An optional parameter. A word that provides auxiliary data |