Add option to disable fadvise() hints

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index 460b456ce44b312a016346a62c30a7a8093bb86b..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
@@ -330,6 +344,14 @@ ioengine=str       Defines how the job issues io to the file. The following
                                will cause that job to do nothing but burn
                                85% of the CPU.
 
+                       guasi   The GUASI IO engine is the Generic Userspace
+                               Asyncronous Syscall Interface approach
+                               to async IO. See
+
+                               http://www.xmailserver.org/guasi-lib.html
+
+                               for more info on GUASI.
+
                        external Prefix to specify loading an external
                                IO engine object file. Append the engine
                                filename, eg ioengine=external:/tmp/foo.o
@@ -539,7 +561,13 @@ verify=str If writing to a file, fio can verify the file contents
 
 stonewall      Wait for preceeding jobs in the job file to exit, before
                starting this one. Can be used to insert serialization
-               points in the job file.
+               points in the job file. A stone wall also implies starting
+               a new reporting group.
+
+new_group      Start a new reporting group. If this option isn't given,
+               jobs in a file will be part of the same reporting group
+               unless seperated by a stone wall (or if it's a group
+               by itself, with the numjobs option).
 
 numjobs=int    Create the specified number of clones of this job. May be
                used to setup a larger number of threads/processes doing
@@ -652,7 +680,7 @@ they denote:
 io=            Number of megabytes io performed
 bw=            Average bandwidth rate
 runt=          The runtime of that thread
-       slat=   Submission latency (avg being the average, dev being the
+       slat=   Submission latency (avg being the average, stdev being the
                standard deviation). This is the time it took to submit
                the io. For sync io, the slat is really the completion
                latency, since queue/complete is one operation there.