Add gtod_reduce option

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index 129926b33be660faae02bc6cef0e4f5f4048cdd3..f4efd281bbc72e2a4a54dfc233aab2310fa0643d 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -835,6 +835,26 @@ cpuchunks=int      If the job is a CPU cycle eater, split the load into
 disk_util=bool Generate disk utilization statistics, if the platform
                supports it. Defaults to on.
 
+disable_clat=bool 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.
+
+disable_slat=bool Disable measurements of submission latency numbers. See
+               disable_clat.
+
+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
 ---------------------------