X-Git-Url: https://gerrit.opnfv.org/gerrit/gitweb?a=blobdiff_plain;f=kernel%2FDocumentation%2Fdevice-mapper%2Fstatistics.txt;h=6f5ef944ca4c8fcdbe9ce8cb06b0bddf0bcdfe59;hb=878d38941df56e0392cb652efe3c5996592e7f39;hp=2a1673adc2004beae034f0ee5d5ae3ef3bceccf8;hpb=9ca8dbcc65cfc63d6f5ef3312a33184e1d726e00;p=kvmfornfv.git

diff --git a/kernel/Documentation/device-mapper/statistics.txt b/kernel/Documentation/device-mapper/statistics.txt
index 2a1673adc..6f5ef944c 100644
--- a/kernel/Documentation/device-mapper/statistics.txt
+++ b/kernel/Documentation/device-mapper/statistics.txt
@@ -13,9 +13,14 @@ 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.  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
@@ -33,7 +38,9 @@ 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 +55,29 @@ 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.
+	  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
@@ -55,6 +85,9 @@ 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
@@ -88,6 +121,10 @@ Messages
 
 	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>]