for using direct IO, though it usually depends on the hardware block size.
This option is mutually exclusive with using a random map for files, so it
will turn off that option.
+.TP
.B zero_buffers
Initialise buffers with all zeros. Default: fill buffers with random data.
.TP
+.B refill_buffers
+If this option is given, fio will refill the IO buffers on every submit. The
+default is to only fill it at init time and reuse that data. Only makes sense
+if zero_buffers isn't specified, naturally. If data verification is enabled,
+refill_buffers is also automatically enabled.
+.TP
.BI nrfiles \fR=\fPint
Number of files to use for this job. Default: 1.
.TP
completely read or written. The same workload will be repeated as many times
as \fBruntime\fR allows.
.TP
+.BI ramp_time \fR=\fPint
+If set, fio will run the specified workload for this amount of time before
+logging any performance numbers. Useful for letting performance settle before
+logging results, thus minimizing the runtime required for stable results. Note
+that the ramp_time is considered lead in time for a job, thus it will increase
+the total runtime if a special timeout or runtime is specified.
+.TP
.BI invalidate \fR=\fPbool
Invalidate buffer-cache for the file prior to starting I/O. Default: true.
.TP
Replay the I/O patterns contained in the specified file generated by
\fBwrite_iolog\fR, or may be a \fBblktrace\fR binary file.
.TP
-.B write_bw_log
-If given, write bandwidth logs of the jobs in this file.
+.B write_bw_log \fR=\fPstr
+If given, write a bandwidth log of the jobs in this job file. Can be used to
+store data of the bandwidth of the jobs in their lifetime. The included
+fio_generate_plots script uses gnuplot to turn these text files into nice
+graphs. See \fBwrite_log_log\fR for behaviour of given filename. For this
+option, the postfix is _bw.log.
.TP
.B write_lat_log
-Same as \fBwrite_bw_log\fR, but writes I/O completion latencies.
+Same as \fBwrite_bw_log\fR, but writes I/O completion latencies. If no
+filename is given with this option, the default filename of "jobname_type.log"
+is used. Even if the filename is given, fio will still append the type of log.
+.TP
+.B disable_clat \fR=\fPbool
+Disable measurements of completion latency numbers. Useful only for cutting
+back the number of calls to gettimeofday, as that does impact performance at
+really high IOPS rates. Note that to really get rid of a large amount of these
+calls, this option must be used with disable_slat and disable_bw as well.
+.TP
+.B disable_slat \fR=\fPbool
+Disable measurements of submission latency numbers. See \fBdisable_clat\fR.
+.TP
+.B disable_bw_measurement \fR=\fPbool
+Disable measurements of throughput/bandwidth numbers. See \fBdisable_clat\fR.
.TP
.BI lockmem \fR=\fPint
Pin the specified amount of memory with \fBmlock\fR\|(2). Can be used to
.TP
.BI disk_util \fR=\fPbool
Generate disk utilization statistics if the platform supports it. Default: true.
+.TP
+.BI gtod_reduce \fR=\fPbool
+Enable all of the gettimeofday() reducing options (disable_clat, disable_slat,
+disable_bw) plus reduce precision of the timeout somewhat to really shrink the
+gettimeofday() call count. With this option enabled, we only do about 0.4% of
+the gtod() calls we would have done if all time keeping was enabled.
+.TP
+.BI gtod_cpu \fR=\fPint
+Sometimes it's cheaper to dedicate a single thread of execution to just getting
+the current time. Fio (and databases, for instance) are very intensive on
+gettimeofday() calls. With this option, you can set one CPU aside for doing
+nothing but logging current time to a shared memory location. Then the other
+threads/processes that run IO workloads need only copy that segment, instead of
+entering the kernel with a gettimeofday() call. The CPU set aside for doing
+these time calls will be excluded from other uses. Fio will manually clear it
+from the CPU mask of other jobs.
.SH OUTPUT
While running, \fBfio\fR will display the status of the created jobs. For
example:
projects / fio.git / blobdiff