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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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BLKPARSE(1) BLKPARSE(1)
blkparse - produce formatted output of event streams of block
devices
blkparse [ options ]
The blkparse utility will attempt to combine streams of events for
various devices on various CPUs, and produce a formatted output of
the event information. Specifically, it will take the (machine-
readable) output of the blktrace utility and convert it to a
nicely formatted and human-readable form.
As with blktrace, some details concerning blkparse will help in
understanding the command line options presented below.
- By default, blkparse expects to run in a post-processing mode;
one where the trace events have been saved by a previous run of
blktrace, and blkparse is combining event streams and dumping
formatted data.
blkparse may be run in a live manner concurrently with blktrace
by specifying -i - to blkparse, and combining it with the live
option for blktrace. An example would be:
% blktrace -d /dev/sda -o - | blkparse -i -
- You can set how many blkparse batches event reads via the -b
option, the default is to handle events in batches of 512.
- If you have saved event traces in blktrace with different output
names (via the -o option to blktrace), you must specify the same
input name via the -i option.
- The format of the output data can be controlled via the -f or -F
options -- see OUTPUT DESCRIPTION AND FORMATTING for details.
By default, blkparse sends formatted data to standard output. This
may be changed via the -o option, or text output can be disabled
via the -O option. A merged binary stream can be produced using
the -d option.
-A hex-mask
--set-mask=hex-mask
Set filter mask to hex-mask, see blktrace (8) for masks
-a mask
--act-mask=mask
Add mask to current filter, see blktrace (8) for masks
-D dir
--input-directory=dir
Prepend dir to input file names
-b batch
--batch={batch}
Standard input read batching
-i file
--input=file
Specifies base name for input files -- default is
device.blktrace.cpu.
As noted above, specifying -i - runs in live mode with
blktrace (reading data from standard in).
-F typ,fmt
--format=typ,fmt
-f fmt
--format-spec=fmt
Sets output format (See OUTPUT DESCRIPTION AND FORMATTING
for details.)
The -f form specifies a format for all events
The -F form allows one to specify a format for a specific
event type. The single-character typ field is one of the
action specifiers described in ACTION IDENTIFIERS.
-M
--no-msgs
When -d is specified, this will stop messages from being
output to the file. (Can seriously reduce the size of the
resultant file when using the CFQ I/O scheduler.)
-h
--hash-by-name
Hash processes by name, not by PID
-o file
--output=file
Output file
-O
--no-text-output
Do not produce text output, used for binary (-d) only
-d file
--dump-binary=file
Binary output file
-q
--quiet
Quiet mode
-s
--per-program-stats
Displays data sorted by program
-S event
--sort-program-stats=event
Displays each program's data sorted by program name or io
event, like Queued, Read, Write and Complete. When -S is
specified the -s will be ignored. The capital letters
Q,R,W,C stand for KB, then q/r/w/c stand for IO.
If you want to soct programs by how many data they queued,
you can use:
blkparse -i sda.blktrace. -q -S Q -o sda.parse
-t
--track-ios
Display time deltas per IO
-w span
--stopwatch=span
Display traces for the span specified -- where span can be:
end-time -- Display traces from time 0 through end-time (in
ns)
or
start:end-time -- Display traces from time start through
end-time (in ns).
-v
--verbose
More verbose marginal on marginal errors
-V
--version
Display version
The following trace actions are recognised:
C -- complete A previously issued request has been completed. The
output will detail the sector and size of that request, as
well as the success or failure of it.
D -- issued A request that previously resided on the block layer
queue or in the i/o scheduler has been sent to the driver.
I -- inserted A request is being sent to the i/o scheduler for
addition to the internal queue and later service by the
driver. The request is fully formed at this time.
Q -- queued This notes intent to queue i/o at the given location.
No real requests exists yet.
B -- bounced The data pages attached to this bio are not reachable
by the hardware and must be bounced to a lower memory
location. This causes a big slowdown in i/o performance, since
the data must be copied to/from kernel buffers. Usually this
can be fixed with using better hardware -- either a better i/o
controller, or a platform with an IOMMU.
M -- back merge A previously inserted request exists that ends on
the boundary of where this i/o begins, so the i/o scheduler
can merge them together.
F -- front merge Same as the back merge, except this i/o ends
where a previously inserted requests starts.
M -- front or back merge One of the above.
G -- get request To send any type of request to a block device, a
struct request container must be allocated first.
S -- sleep No available request structures were available, so the
issuer has to wait for one to be freed.
P -- plug When i/o is queued to a previously empty block device
queue, Linux will plug the queue in anticipation of future ios
being added before this data is needed.
U -- unplug Some request data already queued in the device, start
sending requests to the driver. This may happen automatically
if a timeout period has passed (see next entry) or if a number
of requests have been added to the queue.
T -- unplug due to timer If nobody requests the i/o that was
queued after plugging the queue, Linux will automatically
unplug it after a defined period has passed.
X -- split On raid or device mapper setups, an incoming i/o may
straddle a device or internal zone and needs to be chopped up
into smaller pieces for service. This may indicate a
performance problem due to a bad setup of that raid/dm device,
but may also just be part of normal boundary conditions. dm is
notably bad at this and will clone lots of i/o.
A -- remap For stacked devices, incoming i/o is remapped to device
below it in the i/o stack. The remap action details what
exactly is being remapped to what.
R -- requeue Put a request back on queue.
The output from blkparse can be tailored for specific use -- in
particular, to ease parsing of output, and/or limit output fields
to those the user wants to see. The data for fields which can be
output include:
a Action, a (small) string (1 or 2 characters) -- see table
below for more details
c CPU id
C Command
d RWBS field, a (small) string (1-3 characters) -- see section
below for more details
D 7-character string containing the major and minor numbers of
the event's device (separated by a comma).
e Error value
g Cgroup identifier of the cgroup that generated the IO. Note
that this requires appropriate kernel support (kernel version
at least 4.14).
m Minor number of event's device.
M Major number of event's device.
n Number of blocks
N Number of bytes
p Process ID
P Display packet data -- series of hexadecimal values
s Sequence numbers
S Sector number
t Time stamp (nanoseconds)
T Time stamp (seconds)
u Elapsed value in microseconds (-t command line option)
U Payload unsigned integer
z The absolute time, as local time in your time zone, with no
date displayed
Note that the user can optionally specify field display width, and
optionally a left-aligned specifier. These precede field
specifiers, with a '%' character, followed by the optional left-
alignment specifier (-) followed by the width (a decimal number)
and then the field.
Thus, to specify the command in a 12-character field that is left
aligned:
-f "%-12C"
The following table shows the various actions which may be output:
A IO was remapped to a different device
B IO bounced
C IO completion
D IO issued to driver
F IO front merged with request on queue
G Get request
I IO inserted onto request queue
M IO back merged with request on queue
P Plug request
Q IO handled by request queue code
S Sleep request
T Unplug due to timeout
U Unplug request
X Split
This is a small string containing characters in the following
order:
F Flush
R Read
W Write
D Discard
B Barrier
N Other operation
F Force Unit Access (FUA)
A Readahead
S Synchronous
M Meta
One of 'R', 'W', 'D', or 'N' is always present. The other
characters are optional. Note that 'F' has two meanings, depending
on its position.
The standard header (or initial fields displayed) include:
"%D %2c %8s %5T.%9t %5p %2a %3d"
Breaking this down:
%D Displays the event's device major/minor as: %3d,%-3d.
%2c CPU ID (2-character field).
%8s Sequence number
%5T.%9t
5-character field for the seconds portion of the time stamp
and a 9-character field for the nanoseconds in the time
stamp.
%5p 5-character field for the process ID.
%2a 2-character field for one of the actions.
%3d 3-character field for the RWBS data.
Seeing this in action:
8,0 3 1 0.000000000 697 G W 223490 +
8 [kjournald]
The header is the data in this line up to the 223490
(starting block). The default output for all event types
includes this header.
C -- complete
If a payload is present, this is presented between parenthesis
following the header, followed by the error value.
If no payload is present, the sector and number of blocks are
presented (with an intervening plus (+) character). If the -t
option was specified, then the elapsed time is presented. In
either case, it is followed by the error value for the
completion.
B -- bounced
D -- issued
I -- inserted
Q -- queued
If a payload is present, the number of payload bytes is
output, followed by the payload in hexadecimal between
parenthesis.
If no payload is present, the sector and number of blocks are
presented (with an intervening plus (+) character). If the -t
option was specified, then the elapsed time is presented (in
parenthesis). In either case, it is followed by the command
associated with the event (surrounded by square brackets).
F -- front merge
G -- get request
M -- back merge
S -- sleep
The starting sector and number of blocks is output (with an
intervening plus (+) character), followed by the command
associated with the event (surrounded by square brackets).
P -- plug
The command associated with the event (surrounded by square
brackets) is output.
U -- unplug
T -- unplug due to timer
The command associated with the event (surrounded by square
brackets) is output, followed by the number of requests
outstanding.
X -- split
The original starting sector followed by the new sector
(separated by a slash (/) is output, followed by the command
associated with the event (surrounded by square brackets).
A -- remap
Sector and length is output, along with the original device
and sector offset.
To trace the i/o on the device /dev/sda and parse the output to
human readable form, use the following command:
% blktrace -d /dev/sda -o - | blkparse -i -
(see blktrace (8) for more information). This same behaviour can
be achieve with the convenience script btrace. The command
% btrace /dev/sda
has exactly the same effect as the previous command. See btrace
(8) for more information.
To trace the i/o on a device and save the output for later
processing with blkparse, use blktrace like this:
% blktrace /dev/sda /dev/sdb
This will trace i/o on the devices /dev/sda and /dev/sdb and save
the recorded information in the files sda and sdb in the current
directory, for the two different devices, respectively. This
trace information can later be parsed by the blkparse utility:
% blkparse sda sdb
which will output the previously recorded tracing information in
human readable form to stdout.
blkparse was written by Jens Axboe, Alan D. Brunelle and Nathan
Scott. This man page was created from the blktrace documentation
by Bas Zoetekouw.
Report bugs to <linux-btrace@vger.kernel.org>
Copyright © 2006 Jens Axboe, Alan D. Brunelle and Nathan Scott.
This is free software. You may redistribute copies of it under
the terms of the GNU General Public License
<http://www.gnu.org/licenses/gpl.html>. There is NO WARRANTY, to
the extent permitted by law.
This manual page was created for Debian by Bas Zoetekouw. It was
derived from the documentation provided by the authors and it may
be used, distributed and modified under the terms of the GNU
General Public License, version 2.
On Debian systems, the text of the GNU General Public License can
be found in /usr/share/common-licenses/GPL-2.
btrace(8), blktrace(8), verify_blkparse(1), blkrawverify(1),
btt(1)
This page is part of the blktrace (Linux block layer I/O tracer)
project. Information about the project can be found at [unknown
-- if you know, please contact man-pages@man7.org] It is not known
how to report bugs for this man page; if you know, please send a
mail to man-pages@man7.org. This page was obtained from the
project's upstream Git repository
⟨https://git.kernel.org/pub/scm/linux/kernel/git/axboe/blktrace.git⟩
on 2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-03-20.) If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page,
or you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a
mail to man-pages@man7.org
blktrace git-20070306202522 March 6, 2007 BLKPARSE(1)
Pages that refer to this page: blkrawverify(1), bno_plot(1), btt(1), iowatcher(1), verify_blkparse(1), blkiomon(8), blktrace(8), btrace(8), btrecord(8), btreplay(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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