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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | FILTER MASKS | REQUEST TYPES | EXAMPLES | AUTHORS | REPORTING BUGS | COPYRIGHT | SEE ALSO | COLOPHON |
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BLKTRACE(8) BLKTRACE(8)
blktrace - generate traces of the i/o traffic on block devices
blktrace -d dev [ -r debugfs_path ] [ -o output ] [ -w time ] [
-a action ] [ -A action_mask ] [ -v ]
blktrace is a block layer IO tracing mechanism which provides
detailed information about request queue operations up to user
space. There are three major components: a kernel component, a
utility to record the i/o trace information for the kernel to
user space, and utilities to analyse and view the trace
information. This man page describes blktrace, which records the
i/o event trace information for a specific block device to a
file.
The blktrace utility extracts event traces from the kernel (via
the relaying through the debug file system). Some background
details concerning the run-time behaviour of blktrace will help
to understand some of the more arcane command line options:
- blktrace receives data from the kernel in buffers passed up
through the debug file system (relay). Each device being traced
has a file created in the mounted directory for the debugfs,
which defaults to /sys/kernel/debug -- this can be overridden
with the -r command line argument.
- blktrace defaults to collecting all events that can be traced.
To limit the events being captured, you can specify one or more
filter masks via the -a option.
Alternatively, one may specify the entire mask utilising a
hexadecimal value that is version-specific. (Requires
understanding of the internal representation of the filter
mask.)
- As noted above, the events are passed up via a series of
buffers stored into debugfs files. The size and number of
buffers can be specified via the -b and -n arguments
respectively.
- blktrace stores the extracted data into files stored in the
local directory. The format of the file names is (by default)
device.blktrace.cpu, where device is the base device name (e.g,
if we are tracing /dev/sda, the base device name would be sda);
and cpu identifies a CPU for the event stream.
The device portion of the event file name can be changed via
the -o option.
- blktrace may also be run concurrently with blkparse to produce
live output -- to do this specify -o - for blktrace.
- The default behaviour for blktrace is to run forever until
explicitly killed by the user (via a control-C, or sending
SIGINT signal to the process via invocation the kill (1)
utility). Also you can specify a run-time duration for blktrace
via the -w option -- then blktrace will run for the specified
number of seconds, and then halt.
-A hex-mask
--set-mask=hex-mask
Set filter mask to hex-mask (see below for masks)
-a mask
--act-mask=mask
Add mask to current filter (see below for masks)
-b size
--buffer-size=size
Specifies buffer size for event extraction (scaled by
1024). The default buffer size is 512KiB.
-d dev
--dev=dev
Adds dev as a device to trace
-I file
--input-devs=file
Adds the devices found in file as devices to trace
-n num-sub
--num-sub-buffers=num-sub
Specifies number of buffers to use. blktrace defaults to 4
sub buffers.
-l
--listen
Run in network listen mode (blktrace server)
-h hostname
--host=hostname
Run in network client mode, connecting to the given host
-p number
--port=number
Network port to use (default 8462)
-s
--no-sendfile
Make the network client NOT use sendfile() to transfer
data
-o basename
--output=basename
Specifies base name for input files. Default is
device.blktrace.cpu. Specifying -o - runs in live mode
with blkparse (writing data to standard out).
-D dir
--output-dir=dir
Prepend file to output file name(s)
This only works when supplying a single device, or when
piping the output via "-o -" with multiple devices.
-r rel-path
--relay=rel-path
Specifies debugfs mount point
-v
--version
Outputs version
-V
--version
Outputs version
-w seconds
--stopwatch=seconds
Sets run time to the number of seconds specified
The following masks may be passed with the -a command line
option, multiple filters may be combined via multiple -a command
line options.
barrier: barrier attribute
complete: completed by driver
discard: discard / trim traces
fs: requests
issue: issued to driver
pc: packet command events
queue: queue operations
read: read traces
requeue: requeue operations
sync: synchronous attribute
write: write traces
notify: trace messages
drv_data: additional driver specific trace
blktrace distinguishes between two types of block layer requests,
file system and SCSI commands. The former are dubbed fs requests,
the latter pc requests. File system requests are normal
read/write operations, i.e. any type of read or write from a
specific disk location at a given size. These requests typically
originate from a user process, but they may also be initiated by
the vm flushing dirty data to disk or the file system syncing a
super or journal block to disk. pc requests are SCSI commands.
blktrace sends the command data block as a payload so that
blkparse can decode it.
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 -
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. See blkparse (1) for more
information.
blktrace 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), blkparse(1), 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 2024-06-14. (At that time, the date of the most recent commit
that was found in the repository was 2024-06-12.) 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 BLKTRACE(8)
Pages that refer to this page: blkparse(1), blkrawverify(1), bno_plot(1), btt(1), iowatcher(1), verify_blkparse(1), blkiomon(8), btrace(8), btrecord(8), btreplay(8)
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HTML rendering created 2024-06-26 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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