admin-guide/device-mapper/statistics.rst

5 Device Mapper supports the collection of I/O statistics on user-defined
7 collected so there isn't any performance impact.  Only bio-based DM
10 Each user-defined region specifies a starting sector, length and step.
11 Individual statistics will be collected for each step-sized area within
14 The I/O statistics counters for each step-sized area of a region are
16 Documentation/admin-guide/iostats.rst).  But two extra counters (12 and 13) are
17 provided: total time spent reading and writing.  When the histogram
19 histogram of latencies.  All these counters may be accessed by sending
34 fallback to using vmalloc space.  At most, 1/4 of the overall system
47 	  "-"
50 		a range of <length> 512-byte sectors
72 		to obtain than jiffies-based timestamps.
73 	  histogram:n1,n2,n3,n4,...
74 		collect histogram of latencies.  The
76 		of the histogram.  If precise_timestamps is not used, the
80 		example, if we use "histogram:10,20,30", the kernel will
81 		report four numbers a:b:c:d. a is the number of requests
82 		that took 0-10 ms to complete, b is the number of requests
83 		that took 10-20 ms to complete, c is the number of requests
84 		that took 20-30 ms to complete and d is the number of
111 	Clear all the counters except the in-flight i/o counters.
127 	        precise_timestamps histogram:n1,n2,n3,...
129 	The strings "precise_timestamps" and "histogram" are printed only
133 	Print counters for each step-sized area of a region.
146 	Output format for each step-sized area of a region:
154 	  Please refer to Documentation/admin-guide/iostats.rst for details.
156 	  1. the number of reads completed
175 	in-flight i/o counters.	 Useful when the client consuming the
208   dmsetup message vol 0 @stats_create - /100