1BLKTRACE(8) BLKTRACE(8)
2
6 blktrace - generate traces of the i/o traffic on block devices
7
11 blktrace -d dev [ -r debugfs_path ] [ -o output ] [ -w time ] [ -a
12 action ] [ -A action_mask ] [ -v ]
13
17 blktrace is a block layer IO tracing mechanism which provides detailed
18 information about request queue operations up to user space. There are
19 three major components: a kernel component, a utility to record the i/o
20 trace information for the kernel to user space, and utilities to ana‐
21 lyse and view the trace information. This man page describes blktrace,
22 which records the i/o event trace information for a specific block
23 device to a file.
24 The blktrace utility extracts event traces from the kernel (via the
26 relaying through the debug file system). Some background details con‐
27 cerning the run-time behaviour of blktrace will help to understand some
28 of the more arcane command line options:
29 - blktrace receives data from the kernel in buffers passed up through
32 the debug file system (relay). Each device being traced has a file
33 created in the mounted directory for the debugfs, which defaults to
34 /sys/kernel/debug -- this can be overridden with the -r command line
35 argument.
36 - blktrace defaults to collecting all events that can be traced. To
39 limit the events being captured, you can specify one or more filter
40 masks via the -a option.
41 Alternatively, one may specify the entire mask utilising a hexadeci‐
43 mal value that is version-specific. (Requires understanding of the
44 internal representation of the filter mask.)
45 - As noted above, the events are passed up via a series of buffers
48 stored into debugfs files. The size and number of buffers can be
49 specified via the -b and -n arguments respectively.
50 - blktrace stores the extracted data into files stored in the local
53 directory. The format of the file names is (by default) device.blk‐
54 trace.cpu, where device is the base device name (e.g, if we are trac‐
55 ing /dev/sda, the base device name would be sda); and cpu identifies
56 a CPU for the event stream.
57 The device portion of the event file name can be changed via the -o
59 option.
60 - blktrace may also be run concurrently with blkparse to produce live
63 output -- to do this specify -o - for blktrace.
64 - The default behaviour for blktrace is to run forever until explicitly
67 killed by the user (via a control-C, or sending SIGINT signal to the
68 process via invocation the kill (1) utility). Also you can specify a
69 run-time duration for blktrace via the -w option -- then blktrace
70 will run for the specified number of seconds, and then halt.
71
75 -A hex-mask
76 --set-mask=hex-mask
77 Set filter mask to hex-mask (see below for masks)
78 -a mask
80 --act-mask=mask
81 Add mask to current filter (see below for masks)
82 -b size
84 --buffer-size=size
85 Specifies buffer size for event extraction (scaled by 1024). The
86 default buffer size is 512KiB.
87 -d dev
89 --dev=dev
90 Adds dev as a device to trace
91 -I file
93 --input-devs=file
94 Adds the devices found in file as devices to trace
95 -n num-sub
97 --num-sub-buffers=num-sub
98 Specifies number of buffers to use. blktrace defaults to 4 sub
99 buffers.
100 -l
102 --listen
103 Run in network listen mode (blktrace server)
104 -h hostname
106 --host=hostname
107 Run in network client mode, connecting to the given host
108 -p number
110 --port=number
111 Network port to use (default 8462)
112 -s
114 --no-sendfile
115 Make the network client NOT use sendfile() to transfer data
116 -o basename
118 --output=basename
119 Specifies base name for input files. Default is device.blk‐
120 trace.cpu. Specifying -o - runs in live mode with blkparse
121 (writing data to standard out).
122 -D dir
124 --output-dir=dir
125 Prepend file to output file name(s)
126 This only works when supplying a single device, or when piping
128 the output via "-o -" with multiple devices.
129 -r rel-path
131 --relay=rel-path
132 Specifies debugfs mount point
133 -v
135 --version
136 Outputs version
137 -V
139 --version
140 Outputs version
141 -w seconds
143 --stopwatch=seconds
144 Sets run time to the number of seconds specified
145
149 The following masks may be passed with the -a command line option, mul‐
150 tiple filters may be combined via multiple -a command line options.
151 barrier: barrier attribute
153 complete: completed by driver
154 discard: discard / trim traces
155 fs: requests
156 issue: issued to driver
157 pc: packet command events
158 queue: queue operations
159 read: read traces
160 requeue: requeue operations
161 sync: synchronous attribute
162 write: write traces
163 notify: trace messages
164 drv_data: additional driver specific trace
165
169 blktrace distinguishes between two types of block layer requests, file
170 system and SCSI commands. The former are dubbed fs requests, the latter
171 pc requests. File system requests are normal read/write operations,
172 i.e. any type of read or write from a specific disk location at a
173 given size. These requests typically originate from a user process, but
174 they may also be initiated by the vm flushing dirty data to disk or the
175 file system syncing a super or journal block to disk. pc requests are
176 SCSI commands. blktrace sends the command data block as a payload so
177 that blkparse can decode it.
178
182 To trace the i/o on the device /dev/sda and parse the output to human
183 readable form, use the following command:
184 % blktrace -d /dev/sda -o - | blkparse -i -
186 This same behaviour can be achieve with the convenience script btrace.
188 The command
189 % btrace /dev/sda
191 has exactly the same effect as the previous command. See btrace (8) for
193 more information.
194 To trace the i/o on a device and save the output for later processing
196 with blkparse, use blktrace like this:
197 % blktrace /dev/sda /dev/sdb
199 This will trace i/o on the devices /dev/sda and /dev/sdb and save the
201 recorded information in the files sda and sdb in the current directory,
202 for the two different devices, respectively. This trace information
203 can later be parsed by the blkparse utility:
204 % blkparse sda sdb
206 which will output the previously recorded tracing information in human
208 readable form to stdout. See blkparse (1) for more information.
209
213 blktrace was written by Jens Axboe, Alan D. Brunelle and Nathan Scott.
214 This man page was created from the blktrace documentation by Bas
215 Zoetekouw.
216
220 Report bugs to <linux-btrace@vger.kernel.org>
221
224 Copyright © 2006 Jens Axboe, Alan D. Brunelle and Nathan Scott.
225 This is free software. You may redistribute copies of it under the
226 terms of the GNU General Public License
227 <http://www.gnu.org/licenses/gpl.html>. There is NO WARRANTY, to the
228 extent permitted by law.
229 This manual page was created for Debian by Bas Zoetekouw. It was
230 derived from the documentation provided by the authors and it may be
231 used, distributed and modified under the terms of the GNU General Pub‐
232 lic License, version 2.
233 On Debian systems, the text of the GNU General Public License can be
234 found in /usr/share/common-licenses/GPL-2.
235
238 btrace (8), blkparse (1), verify_blkparse (1), blkrawverify (1), btt
239 (1)
240blktrace git-20070306202522 March 6, 2007 BLKTRACE(8)