This commit / feature adds completion latency histogram output to fio, piggybacking

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index 2c5896d2c212149e65c108f931a589bc681aca29..d4b23c897fb188a99f4794e63769b50ef109b81a 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -1610,6 +1610,14 @@ write_lat_log=str Same as write_bw_log, except that this option stores io
                the filename will not include the job index. See 'Log File
                Formats'.
 
+write_hist_log=str Same as write_lat_log, but writes I/O completion
+               latency histograms. If no filename is given with this option, the
+               default filename of "jobname_clat_hist.x.log" is used, where x is
+               the index of the job (1..N, where N is the number of jobs). Even
+               if the filename is given, fio will still append the type of log.
+               If per_job_logs is false, then the filename will not include the
+               job index. See 'Log File Formats'.
+
 write_iops_log=str Same as write_bw_log, but writes IOPS. If no filename is
                given with this option, the default filename of
                "jobname_type.x.log" is used,where x is the index of the job
@@ -1625,6 +1633,20 @@ log_avg_msec=int By default, fio will log an entry in the iops, latency,
                specified period of time, reducing the resolution of the log.
                See log_max_value as well. Defaults to 0, logging all entries.
 
+log_hist_msec=int Same as log_avg_msec, but logs entries for completion
+               latency histograms. Computing latency percentiles from averages of
+               intervals using log_avg_msec is innacurate. Setting this option makes
+               fio log histogram entries over the specified period of time, reducing
+               log sizes for high IOPS devices while retaining percentile accuracy.
+               See log_hist_coarseness as well. Defaults to 0, meaning histogram
+               logging is disabled.
+
+log_hist_coarseness=int Integer ranging from 0 to 6, defining the coarseness
+               of the resolution of the histogram logs enabled with log_hist_msec. For
+               each increment in coarseness, fio outputs half as many bins. Defaults to
+               0, for which histogram logs contain 1216 latency bins. See
+               'Log File Formats'.
+
 log_max_value=bool     If log_avg_msec is set, fio logs the average over that
                window. If you instead want to log the maximum value, set this
                option to 1. Defaults to 0, meaning that averaged values are