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 kill utility invocation).
70 There are two ways to modify this:
74 You may utilise the blktrace utility itself to kill
75 a running trace -- via the \fB\-k\fR option.
79 You can specify a run-time duration for blktrace via the
80 \fB\-w\fR option -- then blktrace will run for the specified number
81 of seconds, and then halt.
88 \-\-set-mask=\fIhex-mask\fR
90 Set filter mask to \fIhex-mask\fR (see below for masks)
95 \-\-act-mask=\fImask\fR
97 Add \fImask\fR to current filter (see below for masks)
102 \-\-buffer\-size=\fIsize\fR
104 Specifies buffer size for event extraction (scaled by 1024). The default
105 buffer size is 512KiB.
112 Adds \fIdev\fR as a device to trace
117 \-\-input-devs=\fIfile\fR
119 Adds the devices found in \fIfile\fR as devices to trace
131 \-\-num\-sub=\fInum-sub\fR
133 Specifies number of buffers to use. blktrace defaults to 4 sub buffers.
138 \-\-output=\fIfile\fR
140 Prepend \fIfile\fR to output file name(s)
145 \-\-relay=\fIrel-path\fR
147 Specifies debugfs mount point
158 \-\-stopwatch=\fIseconds\fR
160 Sets run time to the number of seconds specified
165 The following masks may be passed with the \fI\-a\fR command line
166 option, multiple filters may be combined via multiple \fI\-a\fR command
170 \fIbarrier\fR: barrier attribute
172 \fIcomplete\fR: completed} by driver
176 \fIissue\fR: issued to driver
178 \fIpc\fR: packet command events
180 \fIqueue\fR: queue operations
182 \fIread\fR: read traces
184 \fIrequeue\fR: requeue operations
186 \fIsync\fR: synchronous attribute
188 \fIwrite\fR: write traces
193 blktrace distinguishes between two types of block layer requests, file system
194 and SCSI commands. The former are dubbed \fBfs\fR requests, the latter
195 \fBpc\fR requests. File system requests are normal read/write operations, i.e.
196 any type of read or write from a specific disk location at a given size. These
197 requests typically originate from a user process, but they may also be
198 initiated by the vm flushing dirty data to disk or the file system syncing a
199 super or journal block to disk. \fBpc\fR requests are SCSI commands. blktrace
200 sends the command data block as a payload so that blkparse can decode it.
204 To trace the i/o on the device \fI/dev/hda\fB and parse the output to human
205 readable form, use the following command:
207 % blktrace \-d /dev/sda \-o \- | blkparse \-i \-
209 This same behaviour can be achieve with the convenience script \fIbtrace\fR.
214 has exactly the same effect as the previous command. See \fIbtrace\fR (8) for
217 To trace the i/o on a device and save the output for later processing with
218 \fIblkparse\fR, use \fIblktrace\fR like this:
220 % blktrace /dev/sda /dev/sdb
222 This will trace i/o on the devices \fI/dev/sda\fR and \fI/dev/sdb\fR and save
223 the recorded information in the files \fIsda\fR and \fIsdb\fR in the current
224 directory, for the two different devices, respectively. This trace
225 information can later be parsed by the \fIblkparse\fR utility:
229 which will output the previously recorded tracing information in human
230 readable form to stdout. See \fIblkparse\fR (1) for more information.
234 blktrace was written by Jens Axboe, Alan D. Brunelle and Nathan Scott. This
235 man page was created from the blktrace documentation by Bas Zoetekouw.
239 Report bugs to <linux\-btrace@vger.kernel.org>
242 Copyright \(co 2006 Jens Axboe, Alan D. Brunelle and Nathan Scott.
244 This is free software. You may redistribute copies of it under the terms of
245 the GNU General Public License <http://www.gnu.org/licenses/gpl.html>.
246 There is NO WARRANTY, to the extent permitted by law.
248 This manual page was created for Debian by Bas Zoetekouw. It was derived from
249 the documentation provided by the authors and it may be used, distributed and
250 modified under the terms of the GNU General Public License, version 2.
252 On Debian systems, the text of the GNU General Public License can be found in
253 /usr/share/common\-licenses/GPL\-2.
256 btrace (8), blkparse (1), verify_blkparse (1), blkrawverify (1), btt (1)