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dm stats: support precise timestamps

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Make it possible to use precise timestamps with nanosecond granularity
in dm statistics.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
This commit is contained in:
Mikulas Patocka
2015-06-09 17:21:39 -04:00
committed by Mike Snitzer
parent dd4c1b7d0c
commit c96aec344d
3 changed files with 127 additions and 43 deletions
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28
Documentation/device-mapper/statistics.txt
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@@ -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