Add support for giving bw/clat/slat log prefixes

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index 1d1aa61d3daf357d734545e83b1ecabb35e237f2..4298f3245daed2b850cc0bcf3077fad48f8404e5 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -804,14 +804,23 @@ read_iolog=str    Open an iolog with the specified file name and replay the
                the file needs to be turned into a blkparse binary data
                file first (blktrace <device> -d file_for_fio.bin).
 
-write_bw_log   If given, write a bandwidth log of the jobs in this job
+write_bw_log=str 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.
+               graphs. See write_log_log for behaviour of given
+               filename. For this option, the postfix is _bw.log.
 
-write_lat_log  Same as write_bw_log, except that this option stores io
-               completion latencies instead.
+write_lat_log=str Same as write_bw_log, except that this option stores io
+               completion latencies instead. 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. So if one specifies
+
+               write_lat_log=foo
+
+               The actual log names will be foo_clat.log and foo_slat.log.
+               This helps fio_generate_plot fine the logs automatically.
 
 lockmem=siint  Pin down the specified amount of memory with mlock(2). Can
                potentially be used instead of removing memory or booting
@@ -848,6 +857,13 @@ disable_slat=bool Disable measurements of submission latency numbers. See
 disable_bw=bool        Disable measurements of throughput/bandwidth numbers. See
                disable_clat.
 
+gtod_reduce=bool 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.
+
 
 6.0 Interpreting the output
 ---------------------------