Add option to disable fadvise() hints

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index 76613714a14a063b4adc3133ee954f2b966748aa..8312d9315ae3a591b7a85cdd0822c86626ace840 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -228,11 +228,25 @@ rw=str            Type of io pattern. Accepted values are:
 
                For the mixed io types, the default is to split them 50/50.
                For certain types of io the result may still be skewed a bit,
-               since the speed may be different.
+               since the speed may be different. It is possible to specify
+               a number of IO's to do before getting a new offset - this
+               is only useful for random IO, where fio would normally
+               generate a new random offset for every IO. If you append
+               eg 8 to randread, you would get a new random offset for
+               every 8 IO's. The result would be a seek for only every 8
+               IO's, instead of for every IO. Use rw=randread:8 to specify
+               that.
 
 randrepeat=bool        For random IO workloads, seed the generator in a predictable
                way so that results are repeatable across repetitions.
 
+fadvise_hint=bool By default, fio will use fadvise() to advise the kernel
+               on what IO patterns it is likely to issue. Sometimes you
+               want to test specific IO patterns without telling the
+               kernel about it, in which case you can disable this option.
+               If set, fio will use POSIX_FADV_SEQUENTIAL for sequential
+               IO and POSIX_FADV_RANDOM for random IO.
+
 size=siint     The total size of file io for this job. This may describe
                the size of the single file the job uses, or it may be
                divided between the number of files in the job. If the