x86-64: correct read/write barriers

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index 0c767dd701c28a16917fcbfd591d22b9e579049b..468772d7227a3a2c9a9cca50436e7c4bc4ebbf0b 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -2339,8 +2339,13 @@ I/O depth
        ``serialize_overlap`` tells fio to avoid provoking this behavior by explicitly
        serializing in-flight I/Os that have a non-zero overlap. Note that setting
        this option can reduce both performance and the :option:`iodepth` achieved.
        ``serialize_overlap`` tells fio to avoid provoking this behavior by explicitly
        serializing in-flight I/Os that have a non-zero overlap. Note that setting
        this option can reduce both performance and the :option:`iodepth` achieved.

-       Additionally this option does not work when :option:`io_submit_mode` is set to
-       offload. Default: false.
+
+       This option only applies to I/Os issued for a single job except when it is
+       enabled along with :option:`io_submit_mode`=offload. In offload mode, fio
+       will check for overlap among all I/Os submitted by offload jobs with :option:`serialize_overlap`
+       enabled.
+
+       Default: false.

 
 .. option:: io_submit_mode=str
 
 
 .. option:: io_submit_mode=str
 


@@ -2504,6 +2509,24 @@ I/O replay
        This limits the influence of the scheduler compared to replaying multiple
        blktraces via concurrent jobs.
 
        This limits the influence of the scheduler compared to replaying multiple
        blktraces via concurrent jobs.
 

+.. option:: merge_blktrace_scalars=float_list
+
+       This is a percentage based option that is index paired with the list of
+       files passed to :option:`read_iolog`. 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
+       :option:`replay_time_scale` which scales the trace during runtime and
+       does not change the output of the merge unlike this option.
+
+.. option:: merge_blktrace_iters=float_list
+
+       This is a whole number option that is index paired with the list of files
+       passed to :option:`read_iolog`. 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.
+

 .. option:: replay_no_stall=bool
 
        When replaying I/O with :option:`read_iolog` the default behavior is to
 .. option:: replay_no_stall=bool
 
        When replaying I/O with :option:`read_iolog` the default behavior is to


@@ -2541,12 +2564,13 @@ I/O replay
 
 .. option:: replay_align=int
 
 
 .. option:: replay_align=int
 

-       Force alignment of I/O offsets and lengths in a trace to this power of 2
-       value.
+       Force alignment of the byte offsets in a trace to this value. The value
+       must be a power of 2.

 
 .. option:: replay_scale=int
 
 
 .. option:: replay_scale=int
 

-       Scale sector offsets down by this factor when replaying traces.
+       Scale byte offsets down by this factor when replaying traces. Should most
+       likely use :option:`replay_align` as well.

 
 .. option:: replay_skip=str
 
 
 .. option:: replay_skip=str
 


@@ -2982,6 +3006,10 @@ Steady state
        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.
 
        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.
 

+       When using this feature, most jobs should include the :option:`time_based`
+       and :option:`runtime` options or the :option:`loops` option so that fio does not
+       stop running after it has covered the full size of the specified file(s) or device(s).
+

                **iops**
                        Collect IOPS data. Stop the job if all individual IOPS measurements
                        are within the specified limit of the mean IOPS (e.g., ``iops:2``
                **iops**
                        Collect IOPS data. Stop the job if all individual IOPS measurements
                        are within the specified limit of the mean IOPS (e.g., ``iops:2``


@@ -3873,6 +3901,24 @@ only file passed to :option:`read_iolog`. An example would look like::
 Creating only the merged file can be done by passing the command line argument
 :option:`merge-blktrace-only`.
 
 Creating only the merged file can be done by passing the command line argument
 :option:`merge-blktrace-only`.
 

+Scaling traces can be done to see the relative impact of any particular trace
+being slowed down or sped up. :option:`merge_blktrace_scalars` takes in a colon
+separated list of percentage scalars. It is index paired with the files passed
+to :option:`read_iolog`.
+
+With scaling, it may be desirable to match the running time of all traces.
+This can be done with :option:`merge_blktrace_iters`. It is index paired with
+:option:`read_iolog` just like :option:`merge_blktrace_scalars`.
+
+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::
+
+       $ fio --read_iolog="<trace_a>:"<trace_b>" --merge_blktrace_file"<output_file>" --merge_blktrace_scalars="50:100" --merge_blktrace_iters="2:1"
+
+This runs trace A at 2x the speed twice for approximately the same runtime as
+a single run of trace B.
+

 
 CPU idleness profiling
 ----------------------
 
 CPU idleness profiling
 ----------------------