1 .TH BLKTRACE 8 "March 6, 2007" "blktrace git\-20070306202522" ""
5 blktrace \- generate traces of the i/o traffic on block devices
9 .B blktrace \-d \fIdev\fR [ \-r \fIdebugfs_path\fR ] [ \-o \fIoutput\fR ] [\-k ] [ \-w \fItime\fR ] [ \-a \fIaction\fR ] [ \-A \fIaction_mask\fR ] [ \-v ]
14 blktrace is a block layer IO tracing mechanism which provides detailed
15 information about request queue operations up to user space. There are three
16 major components: a kernel component, a utility to record the i/o trace
17 information for the kernel to user space, and utilities to analyse and view the
18 trace information. This man page describes blktrace, which records the i/o event
19 trace information for a specific block device to a file.
21 The \fBblktrace\fR utility extracts event traces from the kernel (via
22 the relaying through the debug file system). Some background details
23 concerning the run\-time behaviour of blktrace will help to understand some
24 of the more arcane command line options:
28 blktrace receives data from the kernel in buffers passed up through the
29 debug file system (relay). Each device being traced has a file created in
30 the mounted directory for the debugfs, which defaults to
31 \fI/sys/kernel/debug\fR \-\- this can be overridden with the \fB\-r\fR command
36 blktrace defaults to collecting all events that can be traced. To
37 limit the events being captured, you can specify one or more filter masks
38 via the \fB\-a\fR option.
40 Alternatively, one may specify the entire mask utilising a hexadecimal
41 value that is version\-specific. (Requires understanding of the internal
42 representation of the filter mask.)
46 As noted above, the events are passed up via a series of buffers stored
47 into debugfs files. The size and number of buffers can be specified via
48 the \fB\-b\fR and \fB\-n\fR arguments respectively.
52 blktrace stores the extracted data into files stored in the
53 local directory. The format of the file names is (by default)
54 \fBdevice\fR.\fBblktrace\fR.\fBcpu\fR, where \fBdevice\fR is the base
55 device name (e.g, if we are tracing /dev/sda, the base device name would
56 be \fBsda\fR); and \fBcpu\fR identifies a CPU for the event stream.
58 The \fBdevice\fR portion of the event file name can be changed via
63 blktrace may also be run concurrently with blkparse to produce
64 \fBlive\fR output \-\- to do this specify \fB\-o \-\fR for blktrace.
68 The default behaviour for blktrace is to run forever until explicitly
69 killed by the user (via a control-C, or sending SIGINT signal to the
70 process via invocation the kill (1) utility). Also you can specify a
71 run-time duration for blktrace via the \fB\-w\fR option -- then
72 blktrace will run for the specified number of seconds, and then halt.
79 \-\-set-mask=\fIhex-mask\fR
81 Set filter mask to \fIhex-mask\fR (see below for masks)
86 \-\-act-mask=\fImask\fR
88 Add \fImask\fR to current filter (see below for masks)
93 \-\-buffer\-size=\fIsize\fR
95 Specifies buffer size for event extraction (scaled by 1024). The default
96 buffer size is 512KiB.
103 Adds \fIdev\fR as a device to trace
108 \-\-input-devs=\fIfile\fR
110 Adds the devices found in \fIfile\fR as devices to trace
115 \-\-num\-sub=\fInum-sub\fR
117 Specifies number of buffers to use. blktrace defaults to 4 sub buffers.
122 \-\-output=\fIfile\fR
124 Prepend \fIfile\fR to output file name(s)
129 \-\-relay=\fIrel-path\fR
131 Specifies debugfs mount point
142 \-\-stopwatch=\fIseconds\fR
144 Sets run time to the number of seconds specified
149 The following masks may be passed with the \fI\-a\fR command line
150 option, multiple filters may be combined via multiple \fI\-a\fR command
154 \fIbarrier\fR: barrier attribute
156 \fIcomplete\fR: completed by driver
160 \fIissue\fR: issued to driver
162 \fIpc\fR: packet command events
164 \fIqueue\fR: queue operations
166 \fIread\fR: read traces
168 \fIrequeue\fR: requeue operations
170 \fIsync\fR: synchronous attribute
172 \fIwrite\fR: write traces
174 \fInotify\fR: trace messages
179 blktrace distinguishes between two types of block layer requests, file system
180 and SCSI commands. The former are dubbed \fBfs\fR requests, the latter
181 \fBpc\fR requests. File system requests are normal read/write operations, i.e.
182 any type of read or write from a specific disk location at a given size. These
183 requests typically originate from a user process, but they may also be
184 initiated by the vm flushing dirty data to disk or the file system syncing a
185 super or journal block to disk. \fBpc\fR requests are SCSI commands. blktrace
186 sends the command data block as a payload so that blkparse can decode it.
190 To trace the i/o on the device \fI/dev/hda\fR and parse the output to human
191 readable form, use the following command:
193 % blktrace \-d /dev/sda \-o \- | blkparse \-i \-
195 This same behaviour can be achieve with the convenience script \fIbtrace\fR.
200 has exactly the same effect as the previous command. See \fIbtrace\fR (8) for
203 To trace the i/o on a device and save the output for later processing with
204 \fIblkparse\fR, use \fIblktrace\fR like this:
206 % blktrace /dev/sda /dev/sdb
208 This will trace i/o on the devices \fI/dev/sda\fR and \fI/dev/sdb\fR and save
209 the recorded information in the files \fIsda\fR and \fIsdb\fR in the current
210 directory, for the two different devices, respectively. This trace
211 information can later be parsed by the \fIblkparse\fR utility:
215 which will output the previously recorded tracing information in human
216 readable form to stdout. See \fIblkparse\fR (1) for more information.
220 blktrace was written by Jens Axboe, Alan D. Brunelle and Nathan Scott. This
221 man page was created from the blktrace documentation by Bas Zoetekouw.
225 Report bugs to <linux\-btrace@vger.kernel.org>
228 Copyright \(co 2006 Jens Axboe, Alan D. Brunelle and Nathan Scott.
230 This is free software. You may redistribute copies of it under the terms of
231 the GNU General Public License <http://www.gnu.org/licenses/gpl.html>.
232 There is NO WARRANTY, to the extent permitted by law.
234 This manual page was created for Debian by Bas Zoetekouw. It was derived from
235 the documentation provided by the authors and it may be used, distributed and
236 modified under the terms of the GNU General Public License, version 2.
238 On Debian systems, the text of the GNU General Public License can be found in
239 /usr/share/common\-licenses/GPL\-2.
242 btrace (8), blkparse (1), verify_blkparse (1), blkrawverify (1), btt (1)