X-Git-Url: https://git.kernel.dk/?p=fio.git;a=blobdiff_plain;f=fio.1;h=5c11d963d93dc02d0bf5fd34a3ac6dd633784acb;hp=e28a1fa7b23699696c465399cf2f899d96ac92e1;hb=2c477f4fe896aa059196eac73e569c47050fdfcc;hpb=b9921d1a56d9a6576dcf6c276b380a2a29a112be

diff --git a/fio.1 b/fio.1
index e28a1fa7..5c11d963 100644
--- a/fio.1
+++ b/fio.1
@@ -2209,6 +2209,22 @@ intention here is to make the order of events consistent. This limits the
 influence of the scheduler compared to replaying multiple blktraces via
 concurrent jobs.
 .TP
+.BI merge_blktrace_scalars \fR=\fPfloat_list
+This is a percentage based option that is index paired with the list of files
+passed to \fBread_iolog\fR. When merging is performed, scale the time of each
+event by the corresponding amount. For example,
+`\-\-merge_blktrace_scalars="50:100"' runs the first trace in halftime and the
+second trace in realtime. This knob is separately tunable from
+\fBreplay_time_scale\fR which scales the trace during runtime and will not
+change the output of the merge unlike this option.
+.TP
+.BI merge_blktrace_iters \fR=\fPfloat_list
+This is a whole number option that is index paired with the list of files
+passed to \fBread_iolog\fR. When merging is performed, run each trace for
+the specified number of iterations. For example,
+`\-\-merge_blktrace_iters="2:1"' runs the first trace for two iterations
+and the second trace for one iteration.
+.TP
 .BI replay_no_stall \fR=\fPbool
 When replaying I/O with \fBread_iolog\fR the default behavior is to
 attempt to respect the timestamps within the log and replay them with the
@@ -2655,6 +2671,12 @@ steady state assessment criteria. All assessments are carried out using only
 data from the rolling collection window. Threshold limits can be expressed
 as a fixed value or as a percentage of the mean in the collection window.
 .RS
+.P
+When using this feature, most jobs should include the \fBtime_based\fR
+and \fBruntime\fR options or the \fBloops\fR option so that fio does not
+stop running after it has covered the full size of the specified file(s)
+or device(s).
+.RS
 .RS
 .TP
 .B iops
@@ -3561,6 +3583,26 @@ $ fio \-\-read_iolog="<file1>:<file2>" \-\-merge_blktrace_file="<output_file>"
 .P
 Creating only the merged file can be done by passing the command line argument
 \fBmerge-blktrace-only\fR.
+.P
+Scaling traces can be done to see the relative impact of any particular trace
+being slowed down or sped up. \fBmerge_blktrace_scalars\fR takes in a colon
+separated list of percentage scalars. It is index paired with the files passed
+to \fBread_iolog\fR.
+.P
+With scaling, it may be desirable to match the running time of all traces.
+This can be done with \fBmerge_blktrace_iters\fR. It is index paired with
+\fBread_iolog\fR just like \fBmerge_blktrace_scalars\fR.
+.P
+In an example, given two traces, A and B, each 60s long. If we want to see
+the impact of trace A issuing IOs twice as fast and repeat trace A over the
+runtime of trace B, the following can be done:
+.RS
+.P
+$ fio \-\-read_iolog="<trace_a>:"<trace_b>" \-\-merge_blktrace_file"<output_file>" \-\-merge_blktrace_scalars="50:100" \-\-merge_blktrace_iters="2:1"
+.RE
+.P
+This runs trace A at 2x the speed twice for approximately the same runtime as
+a single run of trace B.
 .SH CPU IDLENESS PROFILING
 In some cases, we want to understand CPU overhead in a test. For example, we
 test patches for the specific goodness of whether they reduce CPU usage.