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Diffstat (limited to 'Documentation/device-mapper')
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diff --git a/Documentation/device-mapper/statistics.txt b/Documentation/device-mapper/statistics.txt new file mode 100644 index 000000000000..2a1673adc200 --- /dev/null +++ b/Documentation/device-mapper/statistics.txt @@ -0,0 +1,186 @@ +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 in milliseconds. All +these counters may be accessed by sending the @stats_print message to +the appropriate DM device via dmsetup. + +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> [<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. + + <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. + + <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> + + @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 auxillary 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 |