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 ] [-k ] [ -w time ] [
12 -a 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 -r rel-path
128 --relay=rel-path
129 Specifies debugfs mount point
130 -v
132 --version
133 Outputs version
134 -V
136 --version
137 Outputs version
138 -w seconds
140 --stopwatch=seconds
141 Sets run time to the number of seconds specified
142
146 The following masks may be passed with the -a command line option, mul‐
147 tiple filters may be combined via multiple -a command line options.
148 barrier: barrier attribute
150 complete: completed by driver
151 fs: requests
152 issue: issued to driver
153 pc: packet command events
154 queue: queue operations
155 read: read traces
156 requeue: requeue operations
157 sync: synchronous attribute
158 write: write traces
159 notify: trace messages
160 drv_data: additional driver specific trace
161
165 blktrace distinguishes between two types of block layer requests, file
166 system and SCSI commands. The former are dubbed fs requests, the latter
167 pc requests. File system requests are normal read/write operations,
168 i.e. any type of read or write from a specific disk location at a
169 given size. These requests typically originate from a user process, but
170 they may also be initiated by the vm flushing dirty data to disk or the
171 file system syncing a super or journal block to disk. pc requests are
172 SCSI commands. blktrace sends the command data block as a payload so
173 that blkparse can decode it.
174
178 To trace the i/o on the device /dev/hda and parse the output to human
179 readable form, use the following command:
180 % blktrace -d /dev/sda -o - | blkparse -i -
182 This same behaviour can be achieve with the convenience script btrace.
184 The command
185 % btrace /dev/sda
187 has exactly the same effect as the previous command. See btrace (8) for
189 more information.
190 To trace the i/o on a device and save the output for later processing
192 with blkparse, use blktrace like this:
193 % blktrace /dev/sda /dev/sdb
195 This will trace i/o on the devices /dev/sda and /dev/sdb and save the
197 recorded information in the files sda and sdb in the current directory,
198 for the two different devices, respectively. This trace information
199 can later be parsed by the blkparse utility:
200 % blkparse sda sdb
202 which will output the previously recorded tracing information in human
204 readable form to stdout. See blkparse (1) for more information.
205
209 blktrace was written by Jens Axboe, Alan D. Brunelle and Nathan Scott.
210 This man page was created from the blktrace documentation by Bas
211 Zoetekouw.
212
216 Report bugs to <linux-btrace@vger.kernel.org>
217
220 Copyright © 2006 Jens Axboe, Alan D. Brunelle and Nathan Scott.
221 This is free software. You may redistribute copies of it under the
222 terms of the GNU General Public License
223 <http://www.gnu.org/licenses/gpl.html>. There is NO WARRANTY, to the
224 extent permitted by law.
225 This manual page was created for Debian by Bas Zoetekouw. It was
226 derived from the documentation provided by the authors and it may be
227 used, distributed and modified under the terms of the GNU General Pub‐
228 lic License, version 2.
229 On Debian systems, the text of the GNU General Public License can be
230 found in /usr/share/common-licenses/GPL-2.
231
234 btrace (8), blkparse (1), verify_blkparse (1), blkrawverify (1), btt
235 (1)
236blktrace git-20070306202522 March 6, 2007 BLKTRACE(8)