Merge branch 'master' into gfio

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index 529c96784117b0955b93fe3f3ad31c3faa58e1e2..a1e659008b38b82e98ba86d0d5d07b4b35b35897 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -1256,6 +1256,22 @@ percentile_list=float_list Overwrite the default list of percentiles
                the values of completion latency below which 99.5% and
                99.9% of the observed latencies fell, respectively.
 
+clocksource=str        Use the given clocksource as the base of timing. The
+               supported options are:
+
+                       gettimeofday    gettimeofday(2)
+
+                       clock_gettime   clock_gettime(2)
+
+                       cpu             Internal CPU clock source
+
+               cpu is the preferred clocksource if it is reliable, as it
+               is very fast (and fio is heavy on time calls). Fio will
+               automatically use this clocksource if it's supported and
+               considered reliable on the system it is running on, unless
+               another clocksource is specifically set. For x86/x86-64 CPUs,
+               this means supporting TSC Invariant.
+
 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