docs: updates for slat, clat, lat percentile reporting

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index f19f9226a93de504d04aad6c60c27856bf1b19cb..d7634790bf7295d0c10dd8414e52adfb3ac1ad10 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -3346,27 +3346,28 @@ Measurements and reporting
        Disable measurements of throughput/bandwidth numbers. See
        :option:`disable_lat`.
 
+.. option:: slat_percentiles=bool
+
+       Report submission latency percentiles. Submission latency is not recorded
+       for synchronous ioengines.
+
 .. option:: clat_percentiles=bool
 
-       Enable the reporting of percentiles of completion latencies.  This
-       option is mutually exclusive with :option:`lat_percentiles`.
+       Report completion latency percentiles.
 
 .. option:: lat_percentiles=bool
 
-       Enable the reporting of percentiles of I/O latencies. This is similar
-       to :option:`clat_percentiles`, except that this includes the
-       submission latency. This option is mutually exclusive with
-       :option:`clat_percentiles`.
+       Report total latency percentiles. Total latency is the sum of submission
+       latency and completion latency.
 
 .. option:: percentile_list=float_list
 
-       Overwrite the default list of percentiles for completion latencies and
-       the block error histogram.  Each number is a floating number in the
-       range (0,100], and the maximum length of the list is 20. Use ``:`` to
-       separate the numbers, and list the numbers in ascending order. For
+       Overwrite the default list of percentiles for latencies and the block error
+       histogram.  Each number is a floating point number in the range (0,100], and
+       the maximum length of the list is 20. Use ``:`` to separate the numbers. For
        example, ``--percentile_list=99.5:99.9`` will cause fio to report the
-       values of completion latency below which 99.5% and 99.9% of the observed
-       latencies fell, respectively.
+       latency durations below which 99.5% and 99.9% of the observed latencies fell,
+       respectively.
 
 .. option:: significant_figures=int