docs: expand description for interval-based bw and iops statistics

Update HOWTO.rst and fio.1 to provide more details about the descriptive
statistics interval-based bw and iops measurements.

Signed-off-by: Vincent Fu <vincent.fu@samsung.com>

diff --git a/HOWTO.rst b/HOWTO.rst
index 0a6e60c77bc7f58176bce88dba759f46c2b38df7..80c08f7ec1ac5ac83d712091f87e244b529afb3a 100644 (file)
--- a/HOWTO.rst
+++ b/HOWTO.rst
@@ -4417,15 +4417,23 @@ writes in the example above).  In the order listed, they denote:
                 It is the sum of submission and completion latency.
 
 **bw**
-               Bandwidth statistics based on samples. Same names as the xlat stats,
-               but also includes the number of samples taken (**samples**) and an
-               approximate percentage of total aggregate bandwidth this thread
-               received in its group (**per**). This last value is only really
-               useful if the threads in this group are on the same disk, since they
-               are then competing for disk access.
+               Bandwidth statistics based on measurements from discrete
+               intervals. Fio continuously monitors bytes transferred and I/O
+               operations completed. By default fio calculates bandwidth in
+               each half-second interval (see :option:`bwavgtime`) and reports
+               descriptive statistics for the measurements here. Same names as
+               the xlat stats, but also includes the number of samples taken
+               (**samples**) and an approximate percentage of total aggregate
+               bandwidth this thread received in its group (**per**). This
+               last value is only really useful if the threads in this group
+               are on the same disk, since they are then competing for disk
+               access.
 
 **iops**
-               IOPS statistics based on samples. Same names as bw.
+               IOPS statistics based on measurements from discrete intervals.
+               For details see the description for bw above. See
+               :option:`iopsavgtime` to control the duration of the intervals.
+               Same values reported here as for bw except for percentage.
 
 **lat (nsec/usec/msec)**
                The distribution of I/O completion latencies. This is the time from when

diff --git a/fio.1 b/fio.1
index 4207814b443e5075a24653badc0530a3f0dbc9c0..e577e2e0130ce96159fe22cb064ec93d9e8690ee 100644 (file)
--- a/fio.1
+++ b/fio.1
@@ -4073,15 +4073,20 @@ Total latency. Same names as slat and clat, this denotes the time from
 when fio created the I/O unit to completion of the I/O operation.
 .TP
 .B bw
-Bandwidth statistics based on samples. Same names as the xlat stats,
-but also includes the number of samples taken (\fIsamples\fR) and an
-approximate percentage of total aggregate bandwidth this thread
-received in its group (\fIper\fR). This last value is only really
-useful if the threads in this group are on the same disk, since they
-are then competing for disk access.
+Bandwidth statistics based on measurements from discrete intervals. Fio
+continuosly monitors bytes transferred and I/O operations completed. By default
+fio calculates bandwidth in each half-second interval (see \fBbwavgtime\fR)
+and reports descriptive statistics for the measurements here. Same names as the
+xlat stats, but also includes the number of samples taken (\fIsamples\fR) and an
+approximate percentage of total aggregate bandwidth this thread received in its
+group (\fIper\fR). This last value is only really useful if the threads in this
+group are on the same disk, since they are then competing for disk access.
 .TP
 .B iops
-IOPS statistics based on samples. Same names as \fBbw\fR.
+IOPS statistics based on measurements from discrete intervals.
+For details see the description for \fBbw\fR above. See
+\fBiopsavgtime\fR to control the duration of the intervals.
+Same values reported here as for \fBbw\fR except for percentage.
 .TP
 .B lat (nsec/usec/msec)
 The distribution of I/O completion latencies. This is the time from when