[PATCH] Don't hide submission latency numbers, even if they are 0.

[fio.git] / README

fio
---

fio is a tool that will spawn a number of threads or processes doing a
particular type of io action as specified by the user. fio takes a
number of global parameters, each inherited by the thread unless
otherwise parameters given to them overriding that setting is given.
The typical use of fio is to write a job file matching the io load
one wants to simulate.


Source
------

fio resides in a git repo, the canonical place is:

git://brick.kernel.dk/data/git/fio.git

Snapshots are frequently generated and they include the git meta data as
well. You can download them here:

http://brick.kernel.dk/snaps/

Pascal Bleser <guru@unixtech.be> has fio RPMs in his repository, you
can find them here:

http://linux01.gwdg.de/~pbleser/rpm-navigation.php?cat=System/fio


Building
--------

Just type 'make' and 'make install'. If on FreeBSD, for now you have to
specify the FreeBSD Makefile with -f, eg:

$ make -f Makefile.Freebsd && make -f Makefile.FreeBSD install

Likewise with OpenSolaris, use the Makefile.solaris to compile there.
This might change in the future if I opt for an autoconf type setup.


Command line
------------

$ fio
	-t <sec> Runtime in seconds
	-l Generate per-job latency logs
	-w Generate per-job bandwidth logs
	-f <file> Read <file> for job descriptions
	-o <file> Log output to file
	-h Print help info
	-v Print version information and exit

Any parameters following the options will be assumed to be job files.
You can add as many as you want, each job file will be regarded as a
separate group and fio will stonewall it's execution.


Job file
--------

Only a few options can be controlled with command line parameters,
generally it's a lot easier to just write a simple job file to describe
the workload. The job file format is in the ini style format, as it's
easy to read and write for the user.

The job file parameters are:

	name=x		Use 'x' as the identifier for this job.
	directory=x	Use 'x' as the top level directory for storing files
	rw=x		'x' may be: read, randread, write, randwrite,
			rw (read-write mix), randrw (read-write random mix)
	rwmixcycle=x	Base cycle for switching between read and write
			in msecs.
	rwmixread=x	'x' percentage of rw mix ios will be reads. If
			rwmixwrite is also given, the last of the two will
			 be used if they don't add up to 100%.
	rwmixwrite=x	'x' percentage of rw mix ios will be writes. See
			rwmixread.
	rand_repeatable=x  The sequence of random io blocks can be repeatable
			across runs, if 'x' is 1.
	size=x		Set file size to x bytes (x string can include k/m/g)
	ioengine=x	'x' may be: aio/libaio/linuxaio for Linux aio,
			posixaio for POSIX aio, sync for regular read/write io,
			mmap for mmap'ed io, splice for using splice/vmsplice,
			or sgio for direct SG_IO io. The latter only works on
			Linux on SCSI (or SCSI-like devices, such as
			usb-storage or sata/libata driven) devices.
	iodepth=x	For async io, allow 'x' ios in flight
	overwrite=x	If 'x', layout a write file first.
	prio=x		Run io at prio X, 0-7 is the kernel allowed range
	prioclass=x	Run io at prio class X
	bs=x		Use 'x' for thread blocksize. May include k/m postfix.
	bsrange=x-y	Mix thread block sizes randomly between x and y. May
			also include k/m postfix.
	direct=x	1 for direct IO, 0 for buffered IO
	thinktime=x	"Think" x usec after each io
	rate=x		Throttle rate to x KiB/sec
	ratemin=x	Quit if rate of x KiB/sec can't be met
	ratecycle=x	ratemin averaged over x msecs
	cpumask=x	Only allow job to run on CPUs defined by mask.
	fsync=x		If writing, fsync after every x blocks have been written
	startdelay=x	Start this thread x seconds after startup
	timeout=x	Terminate x seconds after startup
	offset=x	Start io at offset x (x string can include k/m/g)
	invalidate=x	Invalidate page cache for file prior to doing io
	sync=x		Use sync writes if x and writing
	mem=x		If x == malloc, use malloc for buffers. If x == shm,
			use shm for buffers. If x == mmap, use anon mmap.
	exitall		When one thread quits, terminate the others
	bwavgtime=x	Average bandwidth stats over an x msec window.
	create_serialize=x	If 'x', serialize file creation.
	create_fsync=x	If 'x', run fsync() after file creation.
	end_fsync=x	If 'x', run fsync() after end-of-job.
	loops=x		Run the job 'x' number of times.
	verify=x	If 'x' == md5, use md5 for verifies. If 'x' == crc32,
			use crc32 for verifies. md5 is 'safer', but crc32 is
			a lot faster. Only makes sense for writing to a file.
	stonewall	Wait for preceeding jobs to end before running.
	numjobs=x	Create 'x' similar entries for this job
	thread		Use pthreads instead of forked jobs
	zonesize=x
	zoneskip=y	Zone options must be paired. If given, the job
			will skip y bytes for every x read/written. This
			can be used to gauge hard drive speed over the entire
			platter, without reading everything. Both x/y can
			include k/m/g suffix.
	iolog=x		Open and read io pattern from file 'x'. The file must
			contain one io action per line in the following format:
			rw, offset, length
			where with rw=0/1 for read/write, and the offset
			and length entries being in bytes.
	write_iolog=x	Write an iolog to file 'x' in the same format as iolog.
			The iolog options are exclusive, if both given the
			read iolog will be performed.
	lockmem=x	Lock down x amount of memory on the machine, to
			simulate a machine with less memory available. x can
			include k/m/g suffix.
	nice=x		Run job at given nice value.
	exec_prerun=x	Run 'x' before job io is begun.
	exec_postrun=x	Run 'x' after job io has finished.
	ioscheduler=x	Use ioscheduler 'x' for this job.


Examples using a job file
-------------------------

Example 1) Two random readers

Lets say we want to simulate two threads reading randomly from a file
each. They will be doing IO in 4KiB chunks, using raw (O_DIRECT) IO.
Since they share most parameters, we'll put those in the [global]
section. Job 1 will use a 128MiB file, job 2 will use a 256MiB file.

; ---snip---

[global]
ioengine=sync	; regular read/write(2), the default
rw=randread
bs=4k
direct=1

[file1]
size=128m

[file2]
size=256m

; ---snip---

Generally the [] bracketed name specifies a file name, but the "global"
keyword is reserved for setting options that are inherited by each
subsequent job description. It's possible to have several [global]
sections in the job file, each one adds options that are inherited by
jobs defined below it. The name can also point to a block device, such
as /dev/sda. To run the above job file, simply do:

$ fio jobfile

Example 2) Many random writers

Say we want to exercise the IO subsystem some more. We'll define 64
threads doing random buffered writes. We'll let each thread use async io
with a depth of 4 ios in flight. A job file would then look like this:

; ---snip---

[global]
ioengine=libaio
iodepth=4
rw=randwrite
bs=32k
direct=0
size=64m

[files]
numjobs=64

; ---snip---

This will create files.[0-63] and perform the random writes to them.

There are endless ways to define jobs, the examples/ directory contains
a few more examples.


Interpreting the output
-----------------------

fio spits out a lot of output. While running, fio will display the
status of the jobs created. An example of that would be:

Threads running: 1: [_r] [24.79% done] [eta 00h:01m:31s]

The characters inside the square brackets denote the current status of
each thread. The possible values (in typical life cycle order) are:

Idle	Run
----    ---
P		Thread setup, but not started.
C		Thread created.
I		Thread initialized, waiting.
	R	Running, doing sequential reads.
	r	Running, doing random reads.
	W	Running, doing sequential writes.
	w	Running, doing random writes.
	M	Running, doing mixed sequential reads/writes.
	m	Running, doing mixed random reads/writes.
	F	Running, currently waiting for fsync()
V		Running, doing verification of written data.
E		Thread exited, not reaped by main thread yet.
_		Thread reaped.

The other values are fairly self explanatory - number of threads
currently running and doing io, and the estimated completion percentage
and time for the running group. It's impossible to estimate runtime
of the following groups (if any).

When fio is done (or interrupted by ctrl-c), it will show the data for
each thread, group of threads, and disks in that order. For each data
direction, the output looks like:

Client1 (g=0): err= 0:
  write: io=    32MiB, bw=   666KiB/s, runt= 50320msec
    slat (msec): min=    0, max=  136, avg= 0.03, dev= 1.92
    clat (msec): min=    0, max=  631, avg=48.50, dev=86.82
    bw (KiB/s) : min=    0, max= 1196, per=51.00%, avg=664.02, dev=681.68
  cpu        : usr=1.49%, sys=0.25%, ctx=7969

The client number is printed, along with the group id and error of that
thread. Below is the io statistics, here for writes. In the order listed,
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
		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.
	clat=	Completion latency. Same names as slat, this denotes the
		time from submission to completion of the io pieces. For
		sync io, clat will usually be equal (or very close) to 0,
		as the time from submit to complete is basically just
		CPU time (io has already been done, see slat explanation).
	bw=	Bandwidth. Same names as the xlat stats, but also includes
		an approximate percentage of total aggregate bandwidth
		this thread received in this group. This last value is
		only really useful if the threads in this group are on the
		same disk, since they are then competing for disk access.
cpu=		CPU usage. User and system time, along with the number
		of context switches this thread went through.

After each client has been listed, the group statistics are printed. They
will look like this:

Run status group 0 (all jobs):
   READ: io=64MiB, aggrb=22178, minb=11355, maxb=11814, mint=2840msec, maxt=2955msec
  WRITE: io=64MiB, aggrb=1302, minb=666, maxb=669, mint=50093msec, maxt=50320msec

For each data direction, it prints:

io=		Number of megabytes io performed.
aggrb=		Aggregate bandwidth of threads in this group.
minb=		The minimum average bandwidth a thread saw.
maxb=		The maximum average bandwidth a thread saw.
mint=		The smallest runtime of the threads in that group.
maxt=		The longest runtime of the threads in that group.

And finally, the disk statistics are printed. They will look like this:

Disk stats (read/write):
  sda: ios=16398/16511, merge=30/162, ticks=6853/819634, in_queue=826487, util=100.00%

Each value is printed for both reads and writes, with reads first. The
numbers denote:

ios=		Number of ios performed by all groups.
merge=		Number of merges io the io scheduler.
ticks=		Number of ticks we kept the disk busy.
io_queue=	Total time spent in the disk queue.
util=		The disk utilization. A value of 100% means we kept the disk
		busy constantly, 50% would be a disk idling half of the time.


Author
------

Fio was written by Jens Axboe <axboe@suse.de> to enable flexible testing
of the Linux IO subsystem and schedulers. He got tired of writing
specific test applications to simulate a given workload, and found that
the existing io benchmark/test tools out there weren't flexible enough
to do what he wanted.

Jens Axboe <axboe@suse.de> 20060609