Merge branch 'histograms-PR' of https://github.com/cronburg/fio

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index ca1542d5fdf88b7fa0e6e607ab019a98c5d2d770..0085b7471ff669119b669495b591a3053ff10c32 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -757,7 +757,8 @@ ioengine=str        Defines how the job issues io to the file. The following
                                85% of the CPU. In case of SMP machines,
                                use numjobs=<no_of_cpu> to get desired CPU
                                usage, as the cpuload only loads a single
-                               CPU at the desired rate.
+                               CPU at the desired rate. A job never finishes
+                               unless there is at least one non-cpuio job.
 
                        guasi   The GUASI IO engine is the Generic Userspace
                                Asyncronous Syscall Interface approach
@@ -1174,7 +1175,7 @@ cpus_allowed_policy=str Set the policy of how fio distributes the CPUs
                one cpu per job. If not enough CPUs are given for the jobs
                listed, then fio will roundrobin the CPUs in the set.
 
-numa_cpu_nodes=str Set this job running on spcified NUMA nodes' CPUs. The
+numa_cpu_nodes=str Set this job running on specified NUMA nodes' CPUs. The
                arguments allow comma delimited list of cpu numbers,
                A-B ranges, or 'all'. Note, to enable numa options support,
                fio must be built on a system with libnuma-dev(el) installed.
@@ -1605,10 +1606,18 @@ write_lat_log=str Same as write_bw_log, except that this option stores io
                The actual log names will be foo_slat.x.log, foo_clat.x.log,
                and foo_lat.x.log, where x is the index of the job (1..N,
                where N is the number of jobs). This helps fio_generate_plot
-               fine the logs automatically. If 'per_job_logs' is false, then
+               find the logs automatically. If 'per_job_logs' is false, then
                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
@@ -1624,6 +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
@@ -1839,12 +1862,12 @@ that defines them is selected.
 [psyncv2] hipri                Set RWF_HIPRI on IO, indicating to the kernel that
                        it's of higher priority than normal.
 
-[cpu] cpuload=int Attempt to use the specified percentage of CPU cycles.
+[cpuio] cpuload=int Attempt to use the specified percentage of CPU cycles.
 
-[cpu] cpuchunks=int Split the load into cycles of the given time. In
+[cpuio] cpuchunks=int Split the load into cycles of the given time. In
                microseconds.
 
-[cpu] exit_on_io_done=bool Detect when IO threads are done, then exit.
+[cpuio] exit_on_io_done=bool Detect when IO threads are done, then exit.
 
 [netsplice] hostname=str
 [net] hostname=str The host name or IP address to use for TCP or UDP based IO.