+++ /dev/null
-=============
-DM statistics
-=============
-
-Device Mapper supports the collection of I/O statistics on user-defined
-regions of a DM device. If no regions are defined no statistics are
-collected so there isn't any performance impact. Only bio-based DM
-devices are currently supported.
-
-Each user-defined region specifies a starting sector, length and step.
-Individual statistics will be collected for each step-sized area within
-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. When the histogram
-argument is used, the 14th parameter is reported that represents the
-histogram of latencies. 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
-must be supplied when querying statistics about the region, deleting the
-region, etc. Unique region_ids enable multiple userspace programs to
-request and process statistics for the same DM device without stepping
-on each other's data.
-
-The creation of DM statistics will allocate memory via kmalloc or
-fallback to using vmalloc space. At most, 1/4 of the overall system
-memory may be allocated by DM statistics. The admin can see how much
-memory is used by reading:
-
- /sys/module/dm_mod/parameters/stats_current_allocated_bytes
-
-Messages
-========
-
- @stats_create <range> <step> [<number_of_optional_arguments> <optional_arguments>...] [<program_id> [<aux_data>]]
- Create a new region and return the region_id.
-
- <range>
- "-"
- whole device
- "<start_sector>+<length>"
- a range of <length> 512-byte sectors
- starting with <start_sector>.
-
- <step>
- "<area_size>"
- the range is subdivided into areas each containing
- <area_size> sectors.
- "/<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.
- histogram:n1,n2,n3,n4,...
- collect histogram of latencies. The
- numbers n1, n2, etc are times that represent the boundaries
- of the histogram. If precise_timestamps is not used, the
- times are in milliseconds, otherwise they are in
- nanoseconds. For each range, the kernel will report the
- number of requests that completed within this range. For
- example, if we use "histogram:10,20,30", the kernel will
- report four numbers a:b:c:d. a is the number of requests
- that took 0-10 ms to complete, b is the number of requests
- that took 10-20 ms to complete, c is the number of requests
- that took 20-30 ms to complete and d is the number of
- requests that took more than 30 ms to complete.
-
- <program_id>
- An optional parameter. A name that uniquely identifies
- the userspace owner of the range. This groups ranges together
- so that userspace programs can identify the ranges they
- 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
- that is useful to the client program that created the range.
- The kernel returns this string back in the output of
- @stats_list message, but it doesn't use this value for anything.
-
- @stats_delete <region_id>
- Delete the region with the specified id.
-
- <region_id>
- region_id returned from @stats_create
-
- @stats_clear <region_id>
- Clear all the counters except the in-flight i/o counters.
-
- <region_id>
- region_id returned from @stats_create
-
- @stats_list [<program_id>]
- List all regions registered with @stats_create.
-
- <program_id>
- An optional parameter.
- If this parameter is specified, only matching regions
- are returned.
- If it is not specified, all regions are returned.
-
- Output format:
- <region_id>: <start_sector>+<length> <step> <program_id> <aux_data>
- precise_timestamps histogram:n1,n2,n3,...
-
- The strings "precise_timestamps" and "histogram" are printed only
- if they were specified when creating the region.
-
- @stats_print <region_id> [<starting_line> <number_of_lines>]
- Print counters for each step-sized area of a region.
-
- <region_id>
- region_id returned from @stats_create
-
- <starting_line>
- The index of the starting line in the output.
- If omitted, all lines are returned.
-
- <number_of_lines>
- The number of lines to include in the output.
- If omitted, all lines are returned.
-
- Output format for each step-sized area of a region:
-
- <start_sector>+<length>
- counters
-
- The first 11 counters have the same meaning as
- `/sys/block/*/stat or /proc/diskstats`.
-
- Please refer to Documentation/iostats.txt for details.
-
- 1. the number of reads completed
- 2. the number of reads merged
- 3. the number of sectors read
- 4. the number of milliseconds spent reading
- 5. the number of writes completed
- 6. the number of writes merged
- 7. the number of sectors written
- 8. the number of milliseconds spent writing
- 9. the number of I/Os currently in progress
- 10. the number of milliseconds spent doing I/Os
- 11. the weighted number of milliseconds spent doing I/Os
-
- Additional counters:
-
- 12. the total time spent reading in milliseconds
- 13. the total time spent writing in milliseconds
-
- @stats_print_clear <region_id> [<starting_line> <number_of_lines>]
- Atomically print and then clear all the counters except the
- in-flight i/o counters. Useful when the client consuming the
- statistics does not want to lose any statistics (those updated
- between printing and clearing).
-
- <region_id>
- region_id returned from @stats_create
-
- <starting_line>
- The index of the starting line in the output.
- If omitted, all lines are printed and then cleared.
-
- <number_of_lines>
- The number of lines to process.
- If omitted, all lines are printed and then cleared.
-
- @stats_set_aux <region_id> <aux_data>
- Store auxiliary data aux_data for the specified region.
-
- <region_id>
- region_id returned from @stats_create
-
- <aux_data>
- The string that identifies data which is useful to the client
- program that created the range. The kernel returns this
- string back in the output of @stats_list message, but it
- doesn't use this value for anything.
-
-Examples
-========
-
-Subdivide the DM device 'vol' into 100 pieces and start collecting
-statistics on them::
-
- dmsetup message vol 0 @stats_create - /100
-
-Set the auxiliary data string to "foo bar baz" (the escape for each
-space must also be escaped, otherwise the shell will consume them)::
-
- dmsetup message vol 0 @stats_set_aux 0 foo\\ bar\\ baz
-
-List the statistics::
-
- dmsetup message vol 0 @stats_list
-
-Print the statistics::
-
- dmsetup message vol 0 @stats_print 0
-
-Delete the statistics::
-
- dmsetup message vol 0 @stats_delete 0
projects / linux-2.6-microblaze.git / blobdiff