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

[fio.git] / fio.1

diff --git a/fio.1 b/fio.1
index 85eb0fe981b0d0b89c40e9b714f48f9112778f25..d1acebcdeef1e55f50686ab3cb877ad2aa52ed9b 100644 (file)
--- a/fio.1
+++ b/fio.1
@@ -1476,6 +1476,14 @@ N is the number of jobs). Even if the filename is given, fio will still
 append the type of log. If \fBper_job_logs\fR is false, then the filename will
 not include the job index. See the \fBLOG FILE FORMATS\fR section.
 .TP
+.BI write_hist_log \fR=\fPstr
+Same as \fBwrite_lat_log\fR, 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 \fBper_job_logs\fR is false, then the filename will not
+include the job index. See the \fBLOG FILE FORMATS\fR section.
+.TP
 .BI write_iops_log \fR=\fPstr
 Same as \fBwrite_bw_log\fR, 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
@@ -1496,6 +1504,20 @@ If \fBlog_avg_msec\fR 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 logged.
 .TP
+.BI log_hist_msec \fR=\fPint
+Same as \fBlog_avg_msec\fR, but logs entries for completion latency histograms.
+Computing latency percentiles from averages of intervals using \fBlog_avg_msec\fR
+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 \fBlog_hist_coarseness\fR as well. Defaults
+to 0, meaning histogram logging is disabled.
+.TP
+.BI log_hist_coarseness \fR=\fPint
+Integer ranging from 0 to 6, defining the coarseness of the resolution of the
+histogram logs enabled with \fBlog_hist_msec\fR. For each increment in
+coarseness, fio outputs half as many bins. Defaults to 0, for which histogram
+logs contain 1216 latency bins. See the \fBLOG FILE FORMATS\fR section.
+.TP
 .BI log_offset \fR=\fPbool
 If this is set, the iolog options will include the byte offset for the IO
 entry as well as the other data values.
@@ -2302,6 +2324,13 @@ they aren't applicable if windowed logging is enabled. If windowed logging
 is enabled and \fBlog_max_value\fR is set, then fio logs maximum values in
 that window instead of averages.
 
+For histogram logging the logs look like this:
+
+.B time (msec), data direction, block-size, bin 0, bin 1, ..., bin 1215
+
+Where 'bin i' gives the frequency of IO requests with a latency falling in
+the i-th bin. See \fBlog_hist_coarseness\fR for logging fewer bins.
+
 .RE
 
 .SH CLIENT / SERVER