6. Normal output
7. Terse output
8. Trace file format
+9. CPU idleness profiling
1.0 Overview and history
------------------------
Num threads How many threads or processes should we spread
this workload over.
-
+
The above are the basic parameters defined for a workload, in addition
there's a multitude of parameters that modify other aspects of how this
job behaves.
str String. This is a sequence of alpha characters.
time Integer with possible time suffix. In seconds unless otherwise
specified, use eg 10m for 10 minutes. Accepts s/m/h for seconds,
- minutes, and hours.
+ minutes, and hours, and accepts 'ms' (or 'msec') for milliseconds,
+ and 'us' (or 'usec') for microseconds.
int SI integer. A whole number value, which may contain a suffix
describing the base of the number. Accepted suffixes are k/m/g/t/p,
meaning kilo, mega, giga, tera, and peta. The suffix is not case
can specify a number of files by separating the names with a
':' colon. So if you wanted a job to open /dev/sda and /dev/sdb
as the two working files, you would use
- filename=/dev/sda:/dev/sdb. On Windows, disk devices are accessed
- as \\.\PhysicalDrive0 for the first device, \\.\PhysicalDrive1
- for the second etc. If the wanted filename does need to
- include a colon, then escape that with a '\' character.
- For instance, if the filename is "/dev/dsk/foo@3,0:c",
- then you would use filename="/dev/dsk/foo@3,0\:c".
- '-' is a reserved name, meaning stdin or stdout. Which of the
- two depends on the read/write direction set.
+ filename=/dev/sda:/dev/sdb. On Windows, disk devices are
+ accessed as \\.\PhysicalDrive0 for the first device,
+ \\.\PhysicalDrive1 for the second etc. Note: Windows and
+ FreeBSD prevent write access to areas of the disk containing
+ in-use data (e.g. filesystems).
+ If the wanted filename does need to include a colon, then
+ escape that with a '\' character. For instance, if the filename
+ is "/dev/dsk/foo@3,0:c", then you would use
+ filename="/dev/dsk/foo@3,0\:c". '-' is a reserved name, meaning
+ stdin or stdout. Which of the two depends on the read/write
+ direction set.
+
+filename_format=str
+ If sharing multiple files between jobs, it is usually necessary
+ to have fio generate the exact names that you want. By default,
+ fio will name a file based on the default file format
+ specification of jobname.jobnumber.filenumber. With this
+ option, that can be customized. Fio will recognize and replace
+ the following keywords in this string:
+
+ $jobname
+ The name of the worker thread or process.
+
+ $jobnum
+ The incremental number of the worker thread or
+ process.
+
+ $filenum
+ The incremental number of the file for that worker
+ thread or process.
+
+ To have dependent jobs share a set of files, this option can
+ be set to have fio generate filenames that are shared between
+ the two. For instance, if testfiles.$filenum is specified,
+ file number 4 for any job will be named testfiles.4. The
+ default of $jobname.$jobnum.$filenum will be used if
+ no other format specifier is given.
opendir=str Tell fio to recursively add any file it can find in this
directory and down the file system tree.
same time, but writes get exclusive
access.
- The option may be post-fixed with a lock batch number. If
- set, then each thread/process may do that amount of IOs to
- the file before giving up the lock. Since lock acquisition is
- expensive, batching the lock/unlocks will speed up IO.
-
readwrite=str
rw=str Type of io pattern. Accepted values are:
ten unit instead, for obvious reasons. Allow values are
1024 or 1000, with 1024 being the default.
+unified_rw_reporting=bool Fio normally reports statistics on a per
+ data direction basis, meaning that read, write, and trim are
+ accounted and reported separately. If this option is set,
+ the fio will sum the results and report them as "mixed"
+ instead.
+
randrepeat=bool For random IO workloads, seed the generator in a predictable
way so that results are repeatable across repetitions.
+randseed=int Seed the random number generators based on this seed value, to
+ be able to control what sequence of output is being generated.
+ If not set, the random sequence depends on the randrepeat
+ setting.
+
use_os_rand=bool Fio can either use the random generator supplied by the OS
to generator random offsets, or it can use it's own internal
generator (based on Tausworthe). Default is to use the
fill_device=bool
fill_fs=bool Sets size to something really large and waits for ENOSPC (no
space left on device) as the terminating condition. Only makes
- sense with sequential write. For a read workload, the mount
+ sense with sequential write. For a read workload, the mount
point will be filled first then IO started on the result. This
option doesn't make sense if operating on a raw device node,
since the size of that is already known by the file system.
can be given for both read and writes. If a single int is
given, it will apply to both. If a second int is specified
after a comma, it will apply to writes only. In other words,
- the format is either bs=read_and_write or bs=read,write.
- bs=4k,8k will thus use 4k blocks for reads, and 8k blocks
- for writes. If you only wish to set the write size, you
+ the format is either bs=read_and_write or bs=read,write,trim.
+ bs=4k,8k will thus use 4k blocks for reads, 8k blocks for
+ writes, and 8k for trims. You can terminate the list with
+ a trailing comma. bs=4k,8k, would use the default value for
+ trims.. If you only wish to set the write size, you
can do so by passing an empty read size - bs=,8k will set
8k for writes and leave the read default value.
may be used as a block range. This typically wont work with
direct IO, as that normally requires sector alignment.
+bs_is_seq_rand If this option is set, fio will use the normal read,write
+ blocksize settings as sequential,random instead. Any random
+ read or write will use the WRITE blocksize settings, and any
+ sequential read or write will use the READ blocksize setting.
+
zero_buffers If this option is given, fio will init the IO buffers to
all zeroes. The default is to fill them with random data.
alternate random and zeroed data throughout the IO
buffer.
+buffer_pattern=str If set, fio will fill the io buffers with this pattern.
+ If not set, the contents of io buffers is defined by the other
+ options related to buffer contents. The setting can be any
+ pattern of bytes, and can be prefixed with 0x for hex values.
+
nrfiles=int Number of files to use for this job. Defaults to 1.
openfiles=int Number of files to keep open at the same time. Defaults to
vsync Basic readv(2) or writev(2) IO.
+ psyncv Basic preadv(2) or pwritev(2) IO.
+
libaio Linux native asynchronous io. Note that Linux
may only support queued behaviour with
non-buffered IO (set direct=1 or buffered=0).
channel semantics (Send/Recv) for the
InfiniBand, RoCE and iWARP protocols.
+ falloc IO engine that does regular fallocate to
+ simulate data transfer as fio ioengine.
+ DDIR_READ does fallocate(,mode = keep_size,)
+ DDIR_WRITE does fallocate(,mode = 0)
+ DDIR_TRIM does fallocate(,mode = punch_hole)
+
+ e4defrag IO engine that does regular EXT4_IOC_MOVE_EXT
+ ioctls to simulate defragment activity in
+ request to DDIR_WRITE event
+
external Prefix to specify loading an external
IO engine object file. Append the engine
filename, eg ioengine=external:/tmp/foo.o
O_DIRECT. Note that ZFS on Solaris doesn't support direct io.
On Windows the synchronous ioengines don't support direct io.
+atomic=bool If value is true, attempt to use atomic direct IO. Atomic
+ writes are guaranteed to be stable once acknowledged by
+ the operating system. Only Linux supports O_ATOMIC right
+ now.
+
buffered=bool If value is true, use buffered io. This is the opposite
of the 'direct' option. Defaults to true.
which are intended to operate on a file in parallel in disjoint
segments, with even spacing between the starting points.
+number_ios=int Fio will normally perform IOs until it has exhausted the size
+ of the region set by size=, or if it exhaust the allocated
+ time (or hits an error condition). With this setting, the
+ range/size can be set independently of the number of IOs to
+ perform. When fio reaches this number, it will exit normally
+ and report status.
+
fsync=int If writing to a file, issue a sync of the dirty data
for every number of blocks given. For example, if you give
32 as a parameter, fio will sync the file for every 32
and is large enough for the specified write phase, nothing
will be done.
-end_fsync=bool If true, fsync file contents when the job exits.
+end_fsync=bool If true, fsync file contents when a write stage has completed.
fsync_on_close=bool If true, fio will fsync() a dirty file on close.
This differs from end_fsync in that it will happen on every
if fio is asked to limit reads or writes to a certain rate.
If that is the case, then the distribution may be skewed.
+random_distribution=str:float By default, fio will use a completely uniform
+ random distribution when asked to perform random IO. Sometimes
+ it is useful to skew the distribution in specific ways,
+ ensuring that some parts of the data is more hot than others.
+ fio includes the following distribution models:
+
+ random Uniform random distribution
+ zipf Zipf distribution
+ pareto Pareto distribution
+
+ When using a zipf or pareto distribution, an input value
+ is also needed to define the access pattern. For zipf, this
+ is the zipf theta. For pareto, it's the pareto power. Fio
+ includes a test program, genzipf, that can be used visualize
+ what the given input values will yield in terms of hit rates.
+ If you wanted to use zipf with a theta of 1.2, you would use
+ random_distribution=zipf:1.2 as the option. If a non-uniform
+ model is used, fio will disable use of the random map.
+
+percentage_random=int For a random workload, set how big a percentage should
+ be random. This defaults to 100%, in which case the workload
+ is fully random. It can be set from anywhere from 0 to 100.
+ Setting it to 0 would make the workload fully sequential. Any
+ setting in between will result in a random mix of sequential
+ and random IO, at the given percentages. It is possible to
+ set different values for reads, writes, and trim. To do so,
+ simply use a comma separated list. See blocksize.
+
norandommap Normally fio will cover every block of the file when doing
random IO. If this option is given, fio will just get a
new random offset without looking at past io history. This
will not be as complete as with random maps, this option is
disabled by default.
+random_generator=str Fio supports the following engines for generating
+ IO offsets for random IO:
+
+ tausworthe Strong 2^88 cycle random number generator
+ lfsr Linear feedback shift register generator
+
+ Tausworthe is a strong random number generator, but it
+ requires tracking on the side if we want to ensure that
+ blocks are only read or written once. LFSR guarantees
+ that we never generate the same offset twice, and it's
+ also less computationally expensive. It's not a true
+ random generator, however, though for IO purposes it's
+ typically good enough. LFSR only works with single
+ block sizes, not with workloads that use multiple block
+ sizes. If used with such a workload, fio may read or write
+ some blocks multiple times.
+
nice=int Run the job with the given nice value. See man nice(2).
prio=int Set the io priority value of this job. Linux limits us to
to sleeping for the rest of the period specified by
thinktime.
-thinktime_blocks
+thinktime_blocks=int
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.
+ after every block. This effectively makes any queue depth
+ setting redundant, since no more than 1 IO will be queued
+ before we have to complete it and do our thinktime. In
+ other words, this setting effectively caps the queue depth
+ if the latter is larger.
rate=int Cap the bandwidth used by this job. The number is in bytes/sec,
the normal suffix rules apply. You can use rate=500k to limit
as rate, just specified independently of bandwidth. If the
job is given a block size range instead of a fixed value,
the smallest block size is used as the metric. The same format
- as rate is used for read vs write seperation.
+ as rate is used for read vs write separation.
rate_iops_min=int If fio doesn't meet this rate of IO, it will cause
the job to exit. The same format as rate is used for read vs
- write seperation.
+ write separation.
+
+latency_target=int If set, fio will attempt to find the max performance
+ point that the given workload will run at while maintaining a
+ latency below this target. The values is given in microseconds.
+ See latency_window and latency_percentile
+
+latency_window=int Used with latency_target to specify the sample window
+ that the job is run at varying queue depths to test the
+ performance. The value is given in microseconds.
+
+latency_percentile=float The percentage of IOs that must fall within the
+ criteria specified by latency_target and latency_window. If not
+ set, this defaults to 100.0, meaning that all IOs must be equal
+ or below to the value set by latency_target.
+
+max_latency=int If set, fio will exit the job if it exceeds this maximum
+ latency. It will exit with an ETIME error.
ratecycle=int Average bandwidth for 'rate' and 'ratemin' over this number
of milliseconds.
allows a range of CPUs. Say you wanted a binding to CPUs
1, 5, and 8-15, you would set cpus_allowed=1,5,8-15.
+cpus_allowed_policy=str Set the policy of how fio distributes the CPUs
+ specified by cpus_allowed or cpumask. Two policies are
+ supported:
+
+ shared All jobs will share the CPU set specified.
+ split Each job will get a unique CPU from the CPU set.
+
+ 'shared' is the default behaviour, if the option isn't
+ specified. If split is specified, then fio will will assign
+ one cpu per job. If not enough CPUs are given for the jobs
+ listed, then fio will roundrobin the CPUs in the set.
+
+numa_cpu_nodes=str Set this job running on spcified NUMA nodes' CPUs. The
+ arguments allow comma delimited list of cpu numbers,
+ A-B ranges, or 'all'. Note, to enable numa options support,
+ fio must be built on a system with libnuma-dev(el) installed.
+
+numa_mem_policy=str Set this job's memory policy and corresponding NUMA
+ nodes. Format of the argements:
+ <mode>[:<nodelist>]
+ `mode' is one of the following memory policy:
+ default, prefer, bind, interleave, local
+ For `default' and `local' memory policy, no node is
+ needed to be specified.
+ For `prefer', only one node is allowed.
+ For `bind' and `interleave', it allow comma delimited
+ list of numbers, A-B ranges, or 'all'.
+
startdelay=time Start this job the specified number of seconds after fio
has started. Only useful if the job file contains several
jobs, and you want to delay starting some jobs to a certain
create_on_open=bool Don't pre-setup the files for IO, just create open()
when it's time to do IO to that file.
+create_only=bool If true, fio will only run the setup phase of the job.
+ If files need to be laid out or updated on disk, only
+ that will be done. The actual job contents are not
+ executed.
+
pre_read=bool If this is given, files will be pre-read into memory before
starting the given IO operation. This will also clear
the 'invalidate' flag, since it is pointless to pre-read
to repeat the same workload a given number of times. Defaults
to 1.
+verify_only Do not perform specified workload---only verify data still
+ matches previous invocation of this workload. This option
+ allows one to check data multiple times at a later date
+ without overwriting it. This option makes sense only for
+ workloads that write data, and does not support workloads
+ with the time_based option set.
+
do_verify=bool Run the verify phase after a write phase. Only makes sense if
verify is set. Defaults to 1.
crc7 Use a crc7 sum of the data area and store
it in the header of each block.
+ xxhash Use xxhash as the checksum function. Generally
+ the fastest software checksum that fio
+ supports.
+
sha512 Use sha512 as the checksum function.
sha256 Use sha256 as the checksum function.
meta Write extra information about each io
(timestamp, block number etc.). The block
- number is verified. See also verify_pattern.
+ number is verified. The io sequence number is
+ verified for workloads that write data.
+ See also verify_pattern.
null Only pretend to verify. Useful for testing
internals with ioengine=null, not for much
holding this meta data. If this option is enabled, fio
will write only N blocks before verifying these blocks.
- will verify the previously written blocks before continuing
- to write new ones.
-
verify_backlog_batch=int Control how many blocks fio will verify
if verify_backlog is set. If not set, will default to
the value of verify_backlog (meaning the entire queue
less than verify_backlog then not all blocks will be verified,
if verify_backlog_batch is larger than verify_backlog, some
blocks will be verified more than once.
-
+
stonewall
-wait_for_previous Wait for preceeding jobs in the job file to exit, before
+wait_for_previous Wait for preceding jobs in the job file to exit, before
starting this one. Can be used to insert serialization
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 separated by a stone wall (or if it's a group
- by itself, with the numjobs option).
+new_group Start a new reporting group. See: group_reporting.
numjobs=int Create the specified number of clones of this job. May be
used to setup a larger number of threads/processes doing
- the same thing. We regard that grouping of jobs as a
- specific group.
-
-group_reporting If 'numjobs' is set, it may be interesting to display
- statistics for the group as a whole instead of for each
- individual job. This is especially true of 'numjobs' is
- large, looking at individual thread/process output quickly
- becomes unwieldy. If 'group_reporting' is specified, fio
- will show the final report per-group instead of per-job.
+ the same thing. Each thread is reported separately; to see
+ statistics for all clones as a whole, use group_reporting in
+ conjunction with new_group.
+
+group_reporting It may sometimes be interesting to display statistics for
+ groups of jobs as a whole instead of for each individual job.
+ This is especially true if 'numjobs' is used; looking at
+ individual thread/process output quickly becomes unwieldy.
+ To see the final report per-group instead of per-job, use
+ 'group_reporting'. Jobs in a file will be part of the same
+ reporting group, unless if separated by a stonewall, or by
+ using 'new_group'.
thread fio defaults to forking jobs, however if this option is
given, fio will use pthread_create(3) to create threads
for how to capture such logging data. For blktrace replay,
the file needs to be turned into a blkparse binary data
file first (blkparse <device> -o /dev/null -d file_for_fio.bin).
-
+
replay_no_stall=int When replaying I/O with read_iolog the default behavior
is to attempt to respect the time stamps within the log and
replay them with the appropriate delay between IOPS. By
replay_redirect=str While replaying I/O patterns using read_iolog the
default behavior is to replay the IOPS onto the major/minor
device that each IOP was recorded from. This is sometimes
- undesireable because on a different machine those major/minor
+ undesirable because on a different machine those major/minor
numbers can map to a different device. Changing hardware on
the same system can also result in a different major/minor
mapping. Replay_redirect causes all IOPS to be replayed onto
write_lat_log=foo
- The actual log names will be foo_slat.log, foo_slat.log,
+ The actual log names will be foo_slat.log, foo_clat.log,
and foo_lat.log. This helps fio_generate_plot fine the logs
automatically.
-write_bw_log=str If given, write an IOPS log of the jobs in this job
- file. See write_bw_log.
-
write_iops_log=str Same as write_bw_log, but writes IOPS. If no filename is
given with this option, the default filename of
"jobname_type.log" is used. Even if the filename is given,
lockmem=int Pin down the specified amount of memory with mlock(2). Can
potentially be used instead of removing memory or booting
with less memory to simulate a smaller amount of memory.
+ The amount specified is per worker.
exec_prerun=str Before running this job, issue the command specified
- through system(3).
+ through system(3). Output is redirected in a file called
+ jobname.prerun.txt.
exec_postrun=str After the job completes, issue the command specified
- though system(3).
+ though system(3). Output is redirected in a file called
+ jobname.postrun.txt.
ioscheduler=str Attempt to switch the device hosting the file to the specified
io scheduler before running.
-cpuload=int If the job is a CPU cycle eater, attempt to use the specified
- percentage of CPU cycles.
-
-cpuchunks=int If the job is a CPU cycle eater, split the load into
- cycles of the given time. In microseconds.
-
disk_util=bool Generate disk utilization statistics, if the platform
supports it. Defaults to on.
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
1 Backward-compatible alias for 'all'.
+ignore_error=str Sometimes you want to ignore some errors during test
+ in that case you can specify error list for each error type.
+ ignore_error=READ_ERR_LIST,WRITE_ERR_LIST,VERIFY_ERR_LIST
+ errors for given error type is separated with ':'. Error
+ may be symbol ('ENOSPC', 'ENOMEM') or integer.
+ Example:
+ ignore_error=EAGAIN,ENOSPC:122
+ This option will ignore EAGAIN from READ, and ENOSPC and
+ 122(EDQUOT) from WRITE.
+
+error_dump=bool If set dump every error even if it is non fatal, true
+ by default. If disabled only fatal error will be dumped
+
cgroup=str Add job to this control group. If it doesn't exist, it will
be created. The system must have a mounted cgroup blkio
mount point for this to work. If your system doesn't have it
enabled when polling for a minimum of 0 events (eg when
iodepth_batch_complete=0).
+[cpu] cpuload=int Attempt to use the specified percentage of CPU cycles.
+
+[cpu] cpuchunks=int Split the load into cycles of the given time. In
+ microseconds.
+
[netsplice] hostname=str
[net] hostname=str The host name or IP address to use for TCP or UDP based IO.
If the job is a TCP listener or UDP reader, the hostname is not
- used and must be omitted.
+ used and must be omitted unless it is a valid UDP multicast
+ address.
[netsplice] port=int
[net] port=int The TCP or UDP port to bind to or connect to.
+[netsplice] interface=str
+[net] interface=str The IP address of the network interface used to send or
+ receive UDP multicast
+
+[netsplice] ttl=int
+[net] ttl=int Time-to-live value for outgoing UDP multicast packets.
+ Default: 1
+
+[netsplice] nodelay=bool
+[net] nodelay=bool Set TCP_NODELAY on TCP connections.
+
[netsplice] protocol=str
[netsplice] proto=str
[net] protocol=str
[net] proto=str The network protocol to use. Accepted values are:
tcp Transmission control protocol
- udp Unreliable datagram protocol
+ tcpv6 Transmission control protocol V6
+ udp User datagram protocol
+ udpv6 User datagram protocol V6
unix UNIX domain socket
When the protocol is TCP or UDP, the port must also be given,
[net] listen For TCP network connections, tell fio to listen for incoming
connections rather than initiating an outgoing connection. The
hostname must be omitted if this option is used.
+[net] pingpong Normaly a network writer will just continue writing data, and
+ a network reader will just consume packages. If pingpong=1
+ is set, a writer will send its normal payload to the reader,
+ then wait for the reader to send the same payload back. This
+ allows fio to measure network latencies. The submission
+ and completion latencies then measure local time spent
+ sending or receiving, and the completion latency measures
+ how long it took for the other end to receive and send back.
+ For UDP multicast traffic pingpong=1 should only be set for a
+ single reader when multiple readers are listening to the same
+ address.
+
+[e4defrag] donorname=str
+ File will be used as a block donor(swap extents between files)
+[e4defrag] inplace=int
+ Configure donor file blocks allocation strategy
+ 0(default): Preallocate donor's file on init
+ 1 : allocate space immidietly inside defragment event,
+ and free right after event
+
6.0 Interpreting the output
---- ---
P Thread setup, but not started.
C Thread created.
-I Thread initialized, waiting.
+I Thread initialized, waiting or generating necessary data.
p Thread running pre-reading file(s).
R Running, doing sequential reads.
r Running, doing random reads.
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.
+It is also possible to get fio to dump the current output while it is
+running, without terminating the job. To do that, send fio the USR1 signal.
+You can also get regularly timed dumps by using the --status-interval
+parameter, or by creating a file in /tmp named fio-dump-status. If fio
+sees this file, it will unlink it and dump the current output status.
+
7.0 Terse output
----------------
Read merges, write merges,
Read ticks, write ticks,
Time spent in queue, disk utilization percentage
- Additional Info (dependant on continue_on_error, default off): total # errors, first error code
-
- Additional Info (dependant on description being set): Text description
+ Additional Info (dependent on continue_on_error, default off): total # errors, first error code
+
+ Additional Info (dependent on description being set): Text description
Completion latency percentiles can be a grouping of up to 20 sets, so
for the terse output fio writes all of them. Each field will look like this:
8.0 Trace file format
---------------------
-There are two trace file format that you can encounter. The older (v1) format
+There are two trace file format that you can encounter. The older (v1) format
is unsupported since version 1.20-rc3 (March 2008). It will still be described
below in case that you get an old trace and want to understand it.
The filename is given as an absolute path. The action can be one of these:
add Add the given filename to the trace
-open Open the file with the given filename. The filename has to have
+open Open the file with the given filename. The filename has to have
been added with the add action before.
close Close the file with the given filename. The file has to have been
opened before.
filename action offset length
The filename is given as an absolute path, and has to have been added and opened
-before it can be used with this format. The offset and length are given in
+before it can be used with this format. The offset and length are given in
bytes. The action can be one of these:
wait Wait for 'offset' microseconds. Everything below 100 is discarded.
sync fsync() the file
datasync fdatasync() the file
trim trim the given file from the given 'offset' for 'length' bytes
+
+
+9.0 CPU idleness profiling
+--------------------------
+In some cases, we want to understand CPU overhead in a test. For example,
+we test patches for the specific goodness of whether they reduce CPU usage.
+fio implements a balloon approach to create a thread per CPU that runs at
+idle priority, meaning that it only runs when nobody else needs the cpu.
+By measuring the amount of work completed by the thread, idleness of each
+CPU can be derived accordingly.
+
+An unit work is defined as touching a full page of unsigned characters. Mean
+and standard deviation of time to complete an unit work is reported in "unit
+work" section. Options can be chosen to report detailed percpu idleness or
+overall system idleness by aggregating percpu stats.
projects / fio.git / blobdiff