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 kill utility invocation).
68 There are two ways to modify this:
69 1. You may utilise the blktrace utility itself to kill a running
72 trace -- via the -k option.
73 2. You can specify a run-time duration for blktrace via the -w option
76 -- then blktrace will run for the specified number of seconds, and
77 then halt.
78
82 -A hex-mask
83 --set-mask=hex-mask
84 Set filter mask to hex-mask (see below for masks)
85 -a mask
87 --act-mask=mask
88 Add mask to current filter (see below for masks)
89 -b size
91 --buffer-size=size
92 Specifies buffer size for event extraction (scaled by 1024). The
93 default buffer size is 512KiB.
94 -d dev
96 --dev=dev
97 Adds dev as a device to trace
98 -I file
100 --input-devs=file
101 Adds the devices found in file as devices to trace
102 -k
104 --kill
105 Kill on-going trace
106 -n num-sub
108 --num-sub=num-sub
109 Specifies number of buffers to use. blktrace defaults to 4 sub
110 buffers.
111 -o file
113 --output=file
114 Prepend file to output file name(s)
115 -r rel-path
117 --relay=rel-path
118 Specifies debugfs mount point
119 -V
121 --version Outputs version
122 -w seconds
124 --stopwatch=seconds
125 Sets run time to the number of seconds specified
126
130 The following masks may be passed with the -a command line option, mul‐
131 tiple filters may be combined via multiple -a command line options.
132 barrier: barrier attribute
134 complete: completed by driver
135 fs: requests
136 issue: issued to driver
137 pc: packet command events
138 queue: queue operations
139 read: read traces
140 requeue: requeue operations
141 sync: synchronous attribute
142 write: write traces
143 notify: trace messages
144
148 blktrace distinguishes between two types of block layer requests, file
149 system and SCSI commands. The former are dubbed fs requests, the latter
150 pc requests. File system requests are normal read/write operations,
151 i.e. any type of read or write from a specific disk location at a
152 given size. These requests typically originate from a user process, but
153 they may also be initiated by the vm flushing dirty data to disk or the
154 file system syncing a super or journal block to disk. pc requests are
155 SCSI commands. blktrace sends the command data block as a payload so
156 that blkparse can decode it.
157
161 To trace the i/o on the device /dev/hda and parse the output to human
162 readable form, use the following command:
163 % blktrace -d /dev/sda -o - | blkparse -i -
165 This same behaviour can be achieve with the convenience script btrace.
167 The command
168 % btrace /dev/sda
170 has exactly the same effect as the previous command. See btrace (8) for
172 more information.
173 To trace the i/o on a device and save the output for later processing
175 with blkparse, use blktrace like this:
176 % blktrace /dev/sda /dev/sdb
178 This will trace i/o on the devices /dev/sda and /dev/sdb and save the
180 recorded information in the files sda and sdb in the current directory,
181 for the two different devices, respectively. This trace information
182 can later be parsed by the blkparse utility:
183 % blkparse sda sdb
185 which will output the previously recorded tracing information in human
187 readable form to stdout. See blkparse (1) for more information.
188
192 blktrace was written by Jens Axboe, Alan D. Brunelle and Nathan Scott.
193 This man page was created from the blktrace documentation by Bas
194 Zoetekouw.
195
199 Report bugs to <linux-btrace@vger.kernel.org>
200
203 Copyright © 2006 Jens Axboe, Alan D. Brunelle and Nathan Scott.
204 This is free software. You may redistribute copies of it under the
205 terms of the GNU General Public License
206 <http://www.gnu.org/licenses/gpl.html>. There is NO WARRANTY, to the
207 extent permitted by law.
208 This manual page was created for Debian by Bas Zoetekouw. It was
209 derived from the documentation provided by the authors and it may be
210 used, distributed and modified under the terms of the GNU General Pub‐
211 lic License, version 2.
212 On Debian systems, the text of the GNU General Public License can be
213 found in /usr/share/common-licenses/GPL-2.
214
217 btrace (8), blkparse (1), verify_blkparse (1), blkrawverify (1), btt
218 (1)
219blktrace git-20070306202522 March 6, 2007 BLKTRACE(8)