X-Git-Url: https://git.kernel.dk/?p=fio.git;a=blobdiff_plain;f=HOWTO;h=57c0730b13d0ef7ef8b257a97ff56c1181aa53cf;hp=f5e2449c22d64956015d983c04c1f93aa8dc9840;hb=03b74b3ec5268e731ed7fcaef31c8c0655acd530;hpb=d0bdaf49eb3f4faa941d02274f2bd875a187e7d7

diff --git a/HOWTO b/HOWTO
index f5e2449c..57c0730b 100644
--- a/HOWTO
+++ b/HOWTO
@@ -211,6 +211,9 @@ rw=str		Type of io pattern. Accepted values are:
 		For certain types of io the result may still be skewed a bit,
 		since the speed may be different.
 
+randrepeat=bool	For random IO workloads, seed the generator in a predictable
+		way so that results are repeatable across repetitions.
+
 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
@@ -319,7 +322,13 @@ prioclass=int	Set the io priority class. See man ionice(1).
 
 thinktime=int	Stall the job x microseconds after an io has completed before
 		issuing the next. May be used to simulate processing being
-		done by an application.
+		done by an application. See thinktime_blocks.
+
+thinktime_blocks
+		Only valid if thinktime is set - control how many blocks
+		to issue, before waiting 'thinktime' usecs. If not set,
+		defaults to 1 which will make fio wait 'thinktime' usecs
+		after every block.
 
 rate=int	Cap the bandwidth used by this job to this number of KiB/sec.
 
@@ -338,7 +347,7 @@ startdelay=int	Start this job the specified number of seconds after fio
 		jobs, and you want to delay starting some jobs to a certain
 		time.
 
-timeout=int	Tell fio to terminate processing after the specified number
+runtime=int	Tell fio to terminate processing after the specified number
 		of seconds. It can be quite hard to determine for how long
 		a specified job will run, so this parameter is handy to
 		cap the total runtime to a given time.
@@ -359,15 +368,39 @@ mem=str		Fio can use various types of memory as the io unit buffer.
 
 			shmhuge	Same as shm, but use huge pages as backing.
 
-			mmap	Use anonymous memory maps as the buffers.
-				Allocated through mmap(2).
+			mmap	Use mmap to allocate buffers. May either be
+				anonymous memory, or can be file backed if
+				a filename is given after the option. The
+				format is mem=mmap:/path/to/file.
 
 			mmaphuge Use a memory mapped huge file as the buffer
 				backing. Append filename after mmaphuge, ala
 				mem=mmaphuge:/hugetlbfs/file
 
 		The area allocated is a function of the maximum allowed
-		bs size for the job, multiplied by the io depth given.
+		bs size for the job, multiplied by the io depth given. Note
+		that for shmhuge and mmaphuge to work, the system must have
+		free huge pages allocated. This can normally be checked
+		and set by reading/writing /proc/sys/vm/nr_hugepages on a
+		Linux system. Fio assumes a huge page is 4MiB in size. So
+		to calculate the number of huge pages you need for a given
+		job file, add up the io depth of all jobs (normally one unless
+		iodepth= is used) and multiply by the maximum bs set. Then
+		divide that number by the huge page size. You can see the
+		size of the huge pages in /proc/meminfo. If no huge pages
+		are allocated by having a non-zero number in nr_hugepages,
+		using mmaphuge or shmhuge will fail. Also see hugepage-size.
+
+		mmaphuge also needs to have hugetlbfs mounted and the file
+		location should point there. So if it's mounted in /huge,
+		you would use mem=mmaphuge:/huge/somefile.
+
+hugepage-size=siint
+		Defines the size of a huge page. Must at least be equal
+		to the system setting, see /proc/meminfo. Defaults to 4MiB.
+		Should probably always be a multiple of megabytes, so using
+		hugepage-size=Xm is the preferred way to set this to avoid
+		setting a non-pow-2 bad value.
 
 exitall		When one job finishes, terminate the rest. The default is
 		to wait for each job to finish, sometimes that is not the
@@ -384,7 +417,7 @@ create_serialize=bool	If true, serialize the file creating for the jobs.
 create_fsync=bool	fsync the data file after creation. This is the
 			default.
 
-unlink		Unlink the job files when done. fio defaults to doing this,
+unlink=bool	Unlink the job files when done. fio defaults to doing this,
 		if it created the file itself.
 
 loops=int	Run the specified number of iterations of this job. Used