1 \documentclass{article}
2 \usepackage{epsfig,placeins}
5 % Copyright (C) 2007 Alan D. Brunelle <Alan.Brunelle@hp.com>
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21 % vi :set textwidth=75
23 \title{\texttt{btt} User Guide}
24 \author{Alan D. Brunelle (Alan.Brunelle@hp.com)}
30 \section{\label{sec:intro}Introduction}
32 \texttt{btt} is a post-processing tool for the block layer IO tracing tool called blktrace. As noted in its Users Guide, blktrace
34 is a block layer IO tracing mechanism which provides detailed
35 information about request queue operations up to user space.
38 blktrace is capable of producing tremendous amounts of output in the
39 form of multiple individual traces per IO executed during the traced
40 run. It is also capable of producing some general statistics concerning
41 IO rates and the like. \texttt{btt} goes further and produces a variety
42 of overall statistics about each of the individual handling of IOs, and
43 provides data we believe is useful to plot to provide visual comparisons
46 This document will discuss \texttt{btt} usage, provide some sample output,
47 and also show some interesting plots generated from the data provided
48 by the \texttt{btt} utility.
51 A short note on the ordering of this document -- the actual
52 command-line usage section occurs relatively late in the document (see
53 section~\ref{sec:cmd-line}), as we felt that discussing some of the
54 capabilities and output formats would make the parameter discussion
58 This document refers to the output formats generated by \texttt{btt}
59 version 0.99.1. However, the descriptions are general enough to cover
60 output formats prior to that.
62 \newpage\tableofcontents
64 \newpage\section{\label{sec:getting-started}Getting Started}
66 The simple pipeline to get going with \texttt{btt} is to perform the
70 \item Run \texttt{blktrace}, specifying whatever devices and other
71 parameters you want. You must save the traces to disk in this step,
72 btt does not work in live mode.
74 \item After tracing completes, run \texttt{blkrawverify}, specifying
75 all devices that were traced (or at least on all devices that you
76 will use \texttt{btt} with -- section~\ref{sec:o-D} shows how you
77 can dictate which devices to use with btt). If blkrawverify finds
78 errors in the trace streams saved, it is best to recapture the data
79 -- utilizing \texttt{btt} on \emph{unclean} trace files produces
82 While this step is optional, we have found that performing this
83 helps to ensure data coming from \texttt{btt} makes the most sense.
85 \item Run \texttt{blkparse} with the \texttt{-d} option specifying
86 a file to store the combined binary stream. (e.g.: \texttt{blkparse
89 \texttt{blktrace} produces a series of binary files
90 containing parallel trace streams -- one file per CPU per
91 device. \texttt{blkparse} provides the ability to combine all the
92 files into one time-ordered stream of traces for all devices.
94 \item Run \texttt{btt} specifying the file produced by
95 \texttt{blkparse} utilizing the \texttt{-i} option (e.g.: \texttt{btt
100 \newpage\section{\label{sec:output-overview}Output Overview}
102 The major default areas of output provided by \texttt{btt}
103 include\label{tl-defs}:
106 \item[average component times across all IOs] The time line of each IO
107 is broken down into 3 major regions:
110 \item Time needed to insert or merge an incoming IO onto the request
111 queue. This is the average time from when the IO enters the block
112 IO layer (queue trace) until it is inserted (insert trace) or merged
113 (back merge or front merge trace).
115 This is denoted as \emph{Q2I} time.
117 \item Time spent on the request queue. The average time from when
118 the IO is inserted or merged onto the request queue, until it is
119 issued (issue trace) to the lower level driver.
121 Referred to as \emph{I2D} time\footnote{The \emph{issue} trace
122 is represented by a D in the blkparse output, hence its usage in
123 btt to refer to issue traces. Note that an I is used to refer to
124 \emph{insert} traces.}.
126 \item Driver and device time -- the average time from when the
127 actual IO was issued to the driver until is completed (completion
128 trace) back to the block IO layer.
130 This is referred to as the \emph{D2C} time\
133 Two other sets of results are presented in this section:
136 \item \emph{Q2Q} which measures the time between queue traces
137 in the system. This provides some idea as to how quickly IOs are
138 being handed to the block IO layer.
140 \item \emph{Q2C} which measures the times for the complete life cycle
141 of IOs during the run\footnote{One of the areas that needs some
142 work in \texttt{btt} is to better understand the multiplex nature of
143 IOs during a run. In theory, one would like ${Q2I} + {I2D} + {D2C}
144 = {Q2C}$ however, typically there are multiple queue traces that
145 are combined via merges into a single IO issued and completed. We
146 currently average the queue-to-insert and queue-to-merge times,
147 and thus tend to be quite close to the expected equation.}
151 For each row in this output, we provide a minimum, average, maximum
152 (which are all presented in seconds), and overall count. As an
153 example\footnote{As with this display, the author has taken some liberty
154 in reformatting the output for better display on the printed page.}:
158 ---- ------------- ------------- ------------- -----------
159 Q2Q 0.000000058 0.000012761 9.547941661 2262310
160 Q2I 0.000000272 0.000005995 0.104588839 2262311
161 I2D 0.000001446 0.094992714 0.239636864 2262311
162 D2C 0.000193721 0.030406554 1.634221408 2262311
163 Q2C 0.000207665 0.125405263 1.830917198 2262311
166 \item[Device Overhead]
168 Using the data from the previous chart, we can then provide some idea
169 as to where IO spend most of the time on average. The following output
170 shows the percentage of time spent in each of the 3 phases of an IO:
174 ---------- | ------ ------ ------
175 ( 68, 64) | 0.0% 75.7% 24.2%
178 \item[Device Merge Information]
180 A key measurement when making changes in the system (software \emph{or}
181 hardware) is to understand the block IO layer ends up merging incoming
182 requests into fewer, but larger, IOs to the underlying driver. In this
183 section, we show the number of incoming requests (Q), the number of
184 issued requests (D) and the resultant ratio. We also provide values
185 for the minimum, average and maximum IOs generated.
187 Looking at the following example:
190 DEV | #Q #D Ratio | BLKmin BLKavg BLKmax Total
191 ---------- | ------- ----- ----- | ------ ------ ------ -------
192 ( 68, 64) | 2262311 18178 124.5 | 2 124 128 2262382
195 we see that (on average) the block IO layer is combining upwards of
196 125 incoming requests into a single request down the IO stack. The
197 resultant average IO size is 124 blocks.
199 \item[Device Seek Information]
201 Another useful measure is the variability in the sector distances
202 between consecutive IOs. The next session provides some rudimentary
203 statistics to gauge the general nature of the sector differences
204 between IOs. Values provided include the number of seeks (number of IOs
205 submitted to lower level drivers), the \emph{mean} distance between
206 IOs, the \emph{median} value for all seeks, and the \emph{mode} -
207 the value(s) and the counts are provided for the latter.
210 DEV | NSEEKS MEAN MEDIAN | MODE
211 --------- | ------ ------- ------ | -------
212 ( 68, 64) | 18178 19611.3 0 | 0(17522)
215 We have almost exclusively seen median and mode values of 0, indicating
216 that seeks tend to have an equal amount of forward and backwards
217 seeks. The larger the count for the mode in comparison to the total
218 number of seeks is indicative as to how many IOs are coming out of
219 the block IO layer in adjacent sectors. (Obviously, the higher this
220 percentage, the better the underlying subsystems can handle them.)
223 \item[Request Queue Plug Information]
225 During normal operation, requests queues are \emph{plugged} and during
226 such times the IO request queue elements are not able to be processed
227 by underlying drivers. The next section shows how often the request
228 queue was in such a state.
231 DEV | # Plugs # Timer Us | % Time Q Plugged
232 --------- | ------- ---------- | ----------------
233 ( 68, 64) | 833( 0) | 0.356511895%
236 There are two major reasons why request queues are unplugged, and both
237 are represented in the above table.
240 \item Explicit unplug request from some subsystem in the kernel.
242 \item Timed unplugs, due to a request queue exceeding some temporal
243 limit for being plugged.
246 The total number of unplugs is equal to the number of plugs less the
247 ones due to timer unplugs.
250 \subsection{\label{sec:detailed-data}Detailed Data}
252 In addition to the default sections output, if one supplies the
253 \texttt{--all-data} or \texttt{-A} argument (see section~\ref{sec:o-A})
254 to \texttt{btt} further sections are output:
257 \item[Per Process] As traces are emitted, they are tagged with the
258 process ID of the currently running thread in the kernel. The process
259 names are also preserved, and mapped to the ID. For each of the parts
260 of the time line discussed above on page~\pageref{tl-defs}, a chart is
261 provided which breaks down the traces according to process ID (name).
263 One must be aware, however, that the process ID may not have anything
264 to do with the originating IO. For example, if an application is
265 doing buffered IO, then the actual submitted IOs will most likely
266 come from some page buffer management daemon thread (like pdflush,
267 or kjournald for example). Similarly, completion traces are rarely
268 (if ever?) going to be associated with the process which submitted
269 the IO in the first place.
271 Here is a sample portion of this type of chart, showing Q2Q times
276 ------------- ----------- ----------- ----------- -------
277 mkfs.ext3 0.000000778 0.000009074 1.797176188 1899371
278 mount 0.000000885 0.000672513 0.030638128 73
279 pdflush 0.000000790 0.000006752 0.247231307 179791
282 \item[Per Process Averages] The average columns from the above charts,
283 are also presented in their own chart.
285 \item[Per Device] Similar to the per-process display, \texttt{btt}
286 will also break down the various parts of an IOs time line based upon a
287 per-device criteria. Here's a portion of this area, displayed showing
288 the issued to complete times (D2C).
292 --------- ----------- ----------- ----------- ------
293 ( 65, 80) 0.000140488 0.001076906 0.149739869 169112
294 ( 65, 96) 0.000142762 0.001215221 0.173263182 155488
295 ( 65,112) 0.000145221 0.001254966 0.124929936 165726
296 ( 65,128) 0.000141896 0.001159596 0.775231052 169015
297 ( 65,144) 0.000140832 0.001290985 0.211384698 210661
298 ( 65,160) 0.000139915 0.001175554 0.073512063 133973
299 ( 65,176) 0.000141254 0.001104870 0.073231310 145764
300 ( 65,192) 0.000141453 0.001234460 0.167622507 140618
301 ( 65,208) 0.000143901 0.001126610 0.144651899 178548
302 ( 65,224) 0.000145020 0.001226478 0.124902029 206241
303 ( 65,240) 0.000144315 0.001199571 0.102415459 129154
307 \item[Per Device Averages] The average columns from the above charts,
308 are also presented in their own chart.
311 \newpage\section{\label{sec:data-files}Data Files Output}
313 Besides the averages output by default, the following 3 files are also
314 created with data points which may be plotted.
317 \item[\emph{file}.dat] This file provides a notion of \emph{activity}
318 for the system, devices and processes. The details of this file are
319 provided in section~\ref{sec:activity}.
321 \item[\emph{file}\_qhist.dat] Provides histogram data for the size of
322 incoming IO requests, for more information see section~\ref{sec:qhist}.
324 \item[\emph{file}\_dhist.dat] Provides histogram data for the size
325 of IO requests submitted to lower layer drivers, for more information
326 see section~\ref{sec:dhist}.
330 Besides the default data files output, there are optional data files
331 which can be generated by btt. These include:
334 \item[iostat] iostat-like data can be distilled by btt, and is
335 described in section~\ref{sec:iostat}.
337 \item[per IO detail] Each and every IO traced can be output in a form
338 that shows each of the IO components on consecutive lines (rather
339 than grepping through a blkparse output file for example). The
340 details on this file is included in section~\ref{sec:per-io}.
342 \item[iostat] Latency information -- both Q2C and D2C --
343 on a per-IO basis can be generated. These are described in
344 sections~\ref{sec:lat-q2c} and~\ref{sec:lat-d2c}.
346 \item[seek details] A data file containing all IO-to-IO
347 sector differences can be output, with details found in
348 section~\ref{sec:seek}.
350 \item[unplug histogram details] A data file per device containing
351 histogram output for the amount of IOs released at unplug time.
352 Section~\ref{sec:o-u} has more details.
355 \newpage\section{\label{sec:activity}Activity Data File}
357 The activity data file contains a series of data values that indicate
358 those periods of time when queue and complete traces are being
359 processed. The values happen to be in a format easily handled by
360 xmgrace\footnote{\texttt{http://plasma-gate.weizmann.ac.il/Grace/}
361 ``Grace is a WYSIWYG 2D plotting tool for the X Window System and
362 M*tif.''}, but is easy to parse for other plotting and/or analysis
365 The file is split into pairs of sets of data points, where each pair
366 contains a set of queue activity and a set of completion activity. The
367 points are presented with the first column (X values) being the time
368 (in seconds), and the second column (Y values) providing an on/off
369 type of setting. For each pair, the Y values have two settings off
370 (low) and on (high). For example, here is a snippet of a file showing
375 # Total System : q activity
398 What this indicates is that there was q activity for the system
399 from 0.000000000 through 0.000070381, but was inactive from there to
400 1.023482637, and so on. Section~\ref{sec:o-d} contains details on how
401 to adjust btt's notion of what constitutes activity.
403 The pairs are arranged as follows:
406 \item First there is the total system activity -- meaning activity
407 in either queue or completion traces across all devices.
409 \item Next comes per-device activity information -- for each device
410 being traced, that request queues Q and C traces are presented.
412 \item Last we present pairs per-process.
415 Using this, one is then able to plot regions of activity versus
416 inactivity -- and one can gather a sense of deltas between the queueing
417 of IOs and when they are completed. Figure~\ref{fig:activity} shows
418 a very simplistic chart showing some activity:
421 \leavevmode\centering
422 \epsfig{file=activity.eps,width=4.5in}
423 \caption{\label{fig:activity}Simple Activity Chart}
426 When the black line (system Q activity) is \emph{high}, then the system
427 is seeing relatively continuous incoming queues. Conversely, when it is
428 low, it represents an extended period of time where no queue requests
429 were coming in. Similarly for the red line and C activity.
431 \newpage\section{\label{sec:hist}Histogram Data Files}
433 The histogram data files provide information concerning incoming and
434 outgoing IO sizes (in blocks). For simplicity, the histogram buckets
435 are one-for-one for sizes up to 1,024 blocks in the IO, and then a
436 single bucket for all sizes greater than or equal to 1,024 blocks.
438 The files are again in grace-friendly format, with the first set
439 containing data for the first 1,023 buckets, and a separate set
440 representing sizes $\ge 1024$ blocks. (This is done so that one can
441 easily use a separate formatting specification for the latter set.)
443 The first column (X values) is the various IO sizes, and the second
444 column (Y values) represents the number of IOs of that size.
446 \subsection{\label{sec:qhist}Q Histogram Data File}
448 Figure~\ref{fig:qhist} is a sample graph generated from data used during
449 some real-world analysis\footnote{Note the logarithmic nature of the
450 Y axis for this chart.}. With the visual representation provided by
451 this, one can quickly discern some different characteristics between
452 the 3 runs -- in particular, one can see that there is only a single
453 red point (representing 8 blocks per IO), whereas the other two had
454 multiple data points greater than 8 blocks.
457 \leavevmode\centering
458 \epsfig{file=qhist.eps,width=4.5in}
459 \caption{\label{fig:qhist}Q Histogram}
462 \subsection{\label{sec:dhist}D Histogram Data File}
464 Figure~\ref{fig:dhist} is a sample graph generated from data used during
465 some real-world analysis\footnote{Note the logarithmic nature of the
466 Y axis for this chart.}. Again, visually, one can see that the black
467 and blue dots are somewhat similar below about 192 blocks per IO going
468 out. And then one can make the broad generalization of higher reds,
469 lower blues and blacks in the middle.
472 \leavevmode\centering
473 \epsfig{file=dhist.eps,width=4.5in}
474 \caption{\label{fig:dhist}D Histogram}
477 \newpage\section{\label{sec:iostat}iostat Data File}
478 \texttt{btt} attempts to produce the results from running an
479 \texttt{iostat -x} command in parallel with the system as it is being
480 traced. The fields (columns) generated by the \texttt{--iostat} or
481 \texttt{-I} option can be seen from the following output snippet --
482 note that the line has been split to fit on the printed page:
485 Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s
486 rkB/s wkB/s avgrq-sz avgqu-sz await svctm %util Stamp
488 ( 8, 16) 0.00 0.00 0.00 1005.30 0.00 152806.36
489 0.00 76403.18 152.00 31.00 0.00 0.00 0.00 71.79
491 ( 8, 16) 1.02 5.80 0.34 1.07 4.03 55.62
492 2.02 27.81 42.13 0.61 0.00 21.90 0.00 TOTAL
495 Note that the STAMP field contains the runtime (in seconds) for that
498 \newpage\section{\label{sec:per-io}Per-IO Data File}
500 \texttt{btt} can produce a text file containing time line data for each
501 IO processed. The time line data contains rudimentary information for
502 the following stages:
506 \item get request traces
510 \item completion traces
514 The \emph{--per-io-dump} or \emph{-p} option triggers this behavior,
515 and will produce a file containing streams of IOs (separated by blank
516 spaces), here is an example:
519 20.002179731 8,32 Q 34+8
520 20.002181199 8,32 I 34+8
521 20.098329567 8,32 D 34+16
522 20.002182760 8,32 Q 42+8
523 20.002183613 8,32 M 42+8
524 20.098329567 8,32 D 34+16
525 20.692643206 8,32 C 34+16
528 The columns provide the following information:
531 \item Time of the trace (seconds from the start of the run)
533 \item Device major/minor.
537 \item start block + number of blocks
540 For this pair of initial IOs (Q traces at 20.002179731 and
541 20.002182760), we can follow the insert and merge traces (20.002181199
542 and 20.002183613 respectively), and the issue (duplicate entries for
543 20.098329567), and the completion at 20.692643206. Every Q has its
544 corresponding issue trace bounding any insert or merge operations.
546 \newpage\section{\label{sec:lat}\label{sec:lat-q2c}\label{sec:lat-d2c}Latency Data Files}
548 The latency data files which can be optionally produced by \texttt{btt}
549 provide per-IO latency information, one for total IO time (Q2C) and
550 one for latencies induced by lower layer drivers and devices (D2C).
552 In both cases, the first column (X values) represent runtime (seconds),
553 while the second column (Y values) shows the actual latency for a
554 command at that time (either Q2C or D2C).
556 \newpage\section{\label{sec:seek}Seek Data File}
558 \texttt{btt} can also produce a data file containing all IO-to-IO sector
559 deltas, providing seek information which can then be plotted. The
560 produced data file contains 3 sets of data:
563 \item Combined data -- all read and write IOs
565 \item Read data -- just seek deltas for reads
567 \item Write data -- just seek deltas for writes
570 The format of the data is to have the runtime values (seconds since
571 the start of the run) in column 1 (X values); and the difference in
572 sectors from the previous IO in column 2 (Y values). Here is a snippet
573 of the first few items from a file:
577 0.000034733 35283790.0
578 0.000106453 35283790.0
579 0.005239009 35283950.0
580 0.006968575 35283886.0
581 0.007218709 35283694.0
582 0.012145393 35283566.0
583 0.014980835 -35848914.0
584 0.024239323 -35848914.0
585 0.024249402 -35848914.0
586 0.025707095 -35849072.0
590 Figure~\ref{fig:seek} shows a simple graph that can be produced which
591 provides visual details concerning seek patterns.
594 \leavevmode\centering
595 \epsfig{file=seek.eps,width=4.5in}
596 \caption{\label{fig:seek}Seek Chart}
600 The seek difference is calculated in one of two ways:
603 \item[default] By default, the seek distance is calculated as the
604 \emph{closest} distance between the previous IO and this IO. The
605 concept of \emph{closeness} means that it could either be the
606 \emph{end} of the previous IO and the beginning of the next, or the
607 end of this IO and the start of the next.
609 \item[\texttt{-a}] If the \texttt{-a} or \texttt{--seek-absolute}
610 option is specified, then the seek distance is simply the difference
611 between the end of the previous IO and the start of this IO.
614 \newpage\section{\label{sec:cmd-line}Command Line}
617 Usage: \texttt{btt} 0.99.1
618 [ -a | --seek-absolute ]
620 [ -B <output name> | --dump-blocknos=<output name> ]
621 [ -d <seconds> | --range-delta=<seconds> ]
622 [ -D <dev;...> | --devices=<dev;...> ]
623 [ -e <exe,...> | --exes=<exe,...> ]
625 [ -i <input name> | --input-file=<input name> ]
626 [ -I <output name> | --iostat=<output name> ]
627 [ -l <output name> | --d2c-latencies=<output name> ]
628 [ -M <dev map> | --dev-maps=<dev map>
629 [ -o <output name> | --output-file=<output name> ]
630 [ -p <output name> | --per-io-dump=<output name> ]
631 [ -q <output name> | --q2c-latencies=<output name> ]
632 [ -s <output name> | --seeks=<output name> ]
633 [ -S <interval> | --iostat-interval=<interval> ]
634 [ -t <sec> | --time-start=<sec> ]
635 [ -T <sec> | --time-end=<sec> ]
636 [ -u <output name> | --unplug-hist=<output name> ]
641 \subsection{\label{sec:o-a}\texttt{--seek-absolute}/\texttt{-a}}
643 When specified on the command line, this directs btt to calculate
644 seek distances based solely upon the ending block address of one IO,
645 and the start of the next. By default \texttt{btt} uses the concept
646 of the closeness to either the beginning or end of the previous IO. See
647 section~\ref{sec:seek} for more details about seek distances.
649 \subsection{\label{sec:o-A}\texttt{--all-data}/\texttt{-A}}
651 Normally \texttt{btt} will not print out verbose information
652 concerning per-process and per-device data (as outlined in
653 section~\ref{sec:detailed-data}). If you desire that level of
654 detail you can specify this option.
656 \subsection{\label{sec:o-B}\texttt{--dump-blocknos}/\texttt{-B}}
658 This option will output absolute block numbers to three files prefixed
659 by the specified output name:
662 \item[\emph{prefix}\_\emph{device}\_r.dat] All read block numbers are
663 output, first column is time (seconds), second is the block number,
664 and the third column is the ending block number.
666 \item[\emph{prefix}\_\emph{device}\_w.dat] All write block numbers are
667 output, first column is time (seconds), second is the block number,
668 and the third column is the ending block number.
670 \item[\emph{prefix}\_\emph{device}\_c.dat] All block numbers (read
671 and write) are output, first column is time (seconds), second is
672 the block number, and the third column is the ending block number.
675 \subsection{\label{sec:o-d}\texttt{--range-delta}/\texttt{-d}}
677 Section~\ref{sec:activity} discussed how \texttt{btt} outputs a file
678 containing Q and C activity, the notion of \emph{active} traces simply
679 means that there are Q or C traces occurring within a certain period
680 of each other. The default values is 0.1 seconds; with this option
681 allowing one to change that granularity. The smaller the value, the
682 more data points provided.
684 \subsection{\label{sec:o-D}\texttt{--devices}/\texttt{-D}}
686 Normally, \texttt{btt} will produce data for all devices detected in
687 the traces parsed. With this option, one can reduce the analysis to
688 one or more devices provided in the string passed to this option. The
689 device identifiers are the major and minor number of each device, and
690 each device identifier is separated by a colon (:). A valid specifier
691 for devices 8,0 and 8,8 would then be: \texttt{"8,0:8,8"}.
693 \subsection{\label{sec:o-e}\texttt{--exes}/\texttt{-e}}
695 Likewise, \texttt{btt} will produce data for all processes (executables)
696 found in the traces. With this option, one can specify which processes
697 you want displayed in the output. The format of the string passed is
698 a list of executable \emph{names} separated by commas (,). An example
699 would be \texttt{"-e mkfs.ext3,mount"}.
701 \subsection{\label{sec:o-h}\texttt{--help}/\texttt{-h}}
703 Prints out the simple help information, as seen at the top of
704 section~\ref{sec:cmd-line}.
706 \subsection{\label{sec:o-i}\texttt{--input-file}/\texttt{-i}}
708 Specifies the binary input file that \texttt{btt} will interpret traces
709 in. See section~\ref{sec:getting-started} for information concerning
712 \subsection{\label{sec:o-I}\texttt{--iostat}/\texttt{-I}}
714 This option triggers \texttt{btt} to generate iostat-like output to the
715 file specified. Refer to section~\ref{sec:iostat} for more information
716 on the output produced.
718 \subsection{\label{sec:o-l}\texttt{--d2c-latencies}/\texttt{-l}}
720 This option instructs \texttt{btt} to generate the D2C latency file
721 discussed in section~\ref{sec:lat-d2c}.
723 \subsection{\label{sec:o-M}\texttt{--dev-maps}/\texttt{-M}}
725 Internal option, still under construction.
727 \subsection{\label{sec:o-o}\texttt{--output-file}/\texttt{-o}}
729 Normally \texttt{btt} sends the statistical output (covered in
730 section~\ref{sec:output-overview}) to standard out, if you specify
731 this option this data is redirected to the file specified.
733 \subsection{\label{sec:o-p}\texttt{--per-io-dump}/\texttt{-p}}
735 This option tells \texttt{btt} to generate the per IO dump file as
736 discussed in section~\ref{sec:per-io}.
738 \subsection{\label{sec:o-q}\texttt{--q2c-latencies}/\texttt{-q}}
740 This option instructs \texttt{btt} to generate the Q2C latency file
741 discussed in section~\ref{sec:lat-q2c}.
743 \subsection{\label{sec:o-s}\texttt{--seeks}/\texttt{-s}}
745 This option instructs \texttt{btt} to generate the seek data file
746 discussed in section~\ref{sec:seek}.
748 \subsection{\label{sec:o-S}\texttt{--iostat-interval}/\texttt{-S}}
750 The normal \texttt{iostat} command allows one to specify the snapshot
751 interval, likewise, \texttt{btt} allows one to specify how many seconds
752 between its generation of snapshots of the data via this option. Details
753 about the iostat-like capabilities of \texttt{btt} may be found in
754 section~\ref{sec:iostat}.
756 \subsection{\label{sec:o-tT}\texttt{--time-start}/\texttt{-t} and
757 \texttt{--time-end}/\texttt{T}}
760 \emph{This \texttt{btt} capability is still under construction, results are
761 not always consistent at this point in time.}
764 These options allow one to dictate to \texttt{btt} when to start and stop
765 parsing of trace data in terms of seconds since the start of the run. The
766 trace chosen will be between the start time (or 0.0 if not
767 specified) and end time (or the end of the run) specified.
769 \subsection{\label{sec:o-u}\texttt{--unplug-hist}/\texttt{-u}}
771 This option instructs \texttt{btt} to generate a data file containing
772 histogram information for \emph{unplug} traces on a per device
773 basis. It shows how many times an unplug was hit with a specified
774 number of IOs released. There are 21 output values into the file, as
779 \textbf{X value} & \textbf{Representing Counts} \\\hline
789 The file name(s) generated use the text string passed as an argument for
790 the prefix, followed by the device identifier in \texttt{major,minor}
791 form, with a \texttt{.dat} extension (as an example, with \texttt{-u
792 up\_hist} specified on the command line: \texttt{up\_hist\_008,032.dat}.
794 \subsection{\label{sec:o-V}\texttt{--version}/\texttt{-V}}
796 Prints out the \texttt{btt} version, and exits.
798 \subsection{\label{sec:o-v}\texttt{--verbose}/\texttt{-v}}
800 While \texttt{btt} is processing data, it will put out periodic (1-second
801 granularity) values describing the progress it is making through the
802 input trace stream. The value describes how many traces have been
803 processed. At the end of the run, the overall number of traces, trace
804 rate (number of thousands of traces per second), and the real time for
805 trace processing and output are displayed. Example (note: the interim
806 trace counts are put out with carriage returns, hence, they overwrite
810 # btt -i bp.bin -o btt -v
811 Sending range data to bttX.dat
812 Sending stats data to bttX.avg
817 4581291 traces @ 279.7 Ktps
818 16.379036+0.000005=16.379041
821 \newpage\section*{\label{sec:appendix}Appendix: Sample \texttt{btt}
824 Here is a complete output file from a btt run, illustrating a lot of the
828 ==================== All Devices ====================
831 --------------- ------------- ------------- ------------- -----------
832 Q2Q 0.000000001 0.000015439 0.067431982 4485897
833 Q2I 0.000000277 0.000005085 12.844603081 4485736
834 I2D 0.000000869 0.000721745 12.845117057 4485736
835 D2C 0.000151807 0.005254051 0.097569048 4485736
836 Q2C 0.000156268 0.005980882 12.864868116 4485736
839 \newpage\begin{verbatim}
841 ==================== Device Overhead ====================
844 ---------- | ------ ------ ------
845 ( 8,160) | 0.0% 1.6% 98.4%
846 ( 8,176) | 0.1% 20.0% 79.9%
847 ( 8,208) | 1.2% 69.2% 29.5%
848 ( 65, 32) | 0.0% 1.1% 98.8%
849 ( 65, 64) | 0.0% 3.6% 96.4%
850 ( 65,176) | 0.0% 2.5% 97.4%
851 ( 65, 96) | 0.0% 15.3% 84.6%
852 ( 8,224) | 0.0% 1.7% 98.3%
853 ( 65,112) | 0.0% 2.4% 97.6%
854 ( 8,240) | 0.0% 2.3% 97.7%
855 ( 65,192) | 0.0% 19.4% 80.6%
856 ( 65,240) | 0.0% 1.3% 98.7%
857 ( 65, 48) | 0.0% 2.3% 97.7%
858 ( 8, 32) | 0.0% 7.0% 93.0%
859 ( 66, 80) | 0.1% 9.9% 90.0%
860 ( 66, 32) | 0.0% 0.7% 99.3%
861 ( 65,224) | 0.0% 18.1% 81.9%
862 ( 65,144) | 0.1% 39.5% 60.5%
863 ( 8,144) | 0.0% 0.7% 99.3%
864 ( 66,144) | 0.0% 1.5% 98.5%
865 ( 66,128) | 0.0% 3.0% 97.0%
866 ( 66,176) | 0.0% 12.5% 87.4%
867 ( 66,224) | 0.0% 10.2% 89.8%
868 ( 66,192) | 0.0% 2.1% 97.9%
869 ( 66,160) | 0.0% 9.4% 90.5%
870 ( 66,240) | 0.0% 9.8% 90.2%
871 ( 66,112) | 0.1% 24.2% 75.7%
872 ( 8, 64) | 0.0% 9.6% 90.4%
873 ( 65,160) | 0.2% 26.2% 73.7%
874 ( 65,208) | 0.0% 2.0% 98.0%
875 ( 66, 16) | 0.0% 4.5% 95.5%
876 ( 65, 0) | 0.0% 2.2% 97.8%
877 ( 65, 16) | 0.0% 1.8% 98.1%
878 ( 66,208) | 0.0% 2.7% 97.3%
879 ( 8,128) | 0.2% 23.7% 76.1%
880 ( 65, 80) | 0.0% 20.0% 80.0%
881 ( 8,112) | 0.0% 1.2% 98.7%
882 ( 65,128) | 0.0% 1.9% 98.1%
883 ( 66, 64) | 0.0% 12.1% 87.9%
884 ( 66, 0) | 0.0% 7.2% 92.8%
885 ( 66, 48) | 0.0% 2.6% 97.4%
886 ( 8,192) | 0.0% 2.3% 97.7%
887 ( 67, 16) | 0.0% 0.8% 99.2%
888 ( 66, 96) | 0.0% 12.3% 87.7%
889 ( 8, 96) | 0.0% 10.3% 89.7%
890 ( 8, 80) | 0.0% 1.7% 98.3%
891 ( 8, 48) | 0.0% 0.7% 99.2%
892 ( 67, 0) | 0.0% 2.6% 97.4%
895 \newpage\begin{verbatim}
897 ==================== Device Merge Information ====================
899 DEV | #Q #D Ratio | BLKmin BLKavg BLKmax Total
900 ---------- | -------- -------- ------- | -------- -------- -------- --------
901 ( 8,160) | 75145 47890 1.6 | 8 12 1024 601160
902 ( 8,176) | 91374 55492 1.6 | 8 13 1024 730992
903 ( 8,208) | 101039 63944 1.6 | 8 12 1024 809256
904 ( 65, 32) | 67919 44494 1.5 | 8 12 1024 543352
905 ( 65, 64) | 114614 77396 1.5 | 8 11 1024 916968
906 ( 65,176) | 93808 62746 1.5 | 8 11 1024 750464
907 ( 65, 96) | 95537 51705 1.8 | 8 14 1024 764296
908 ( 8,224) | 95435 49753 1.9 | 8 15 1024 765560
909 ( 65,112) | 100020 63530 1.6 | 8 12 1024 800160
910 ( 8,240) | 72282 44700 1.6 | 8 12 1024 578256
911 ( 65,192) | 95175 59010 1.6 | 8 12 1024 761400
912 ( 65,240) | 86334 53548 1.6 | 8 12 1024 690984
913 ( 65, 48) | 69623 44652 1.6 | 8 12 1024 556984
914 ( 8, 32) | 97816 63116 1.5 | 8 12 1024 782528
915 ( 66, 80) | 110873 71526 1.6 | 8 12 1024 886984
916 ( 66, 32) | 79242 53134 1.5 | 8 11 1024 633936
917 ( 65,224) | 122788 66180 1.9 | 8 14 1024 982304
918 ( 65,144) | 116636 70205 1.7 | 8 13 1024 933416
919 ( 8,144) | 72014 49047 1.5 | 8 11 1024 576112
920 ( 66,144) | 109244 70613 1.5 | 8 12 1024 873952
921 ( 66,128) | 104688 65381 1.6 | 8 12 1024 837504
922 ( 66,176) | 79627 47894 1.7 | 8 13 1024 637016
923 ( 66,224) | 88754 58159 1.5 | 8 12 1024 710032
924 ( 66,192) | 88919 55417 1.6 | 8 12 1024 711464
925 ( 66,160) | 102908 71156 1.4 | 8 11 1024 823264
926 ( 66,240) | 94190 66472 1.4 | 8 11 1024 753520
927 ( 66,112) | 138799 82027 1.7 | 8 13 1024 1110392
928 ( 8, 64) | 105011 63892 1.6 | 8 13 1024 840112
929 ( 65,160) | 93383 55579 1.7 | 8 13 1024 747064
930 ( 65,208) | 109771 67987 1.6 | 8 12 1024 878168
931 ( 66, 16) | 96703 56613 1.7 | 8 13 1024 773624
932 ( 65, 0) | 83752 51532 1.6 | 8 13 1024 670032
933 ( 65, 16) | 64538 35982 1.8 | 8 14 1024 516320
934 ( 66,208) | 90636 54306 1.7 | 8 13 1024 725088
935 ( 8,128) | 96202 59653 1.6 | 8 13 1024 776192
936 ( 65, 80) | 107945 65672 1.6 | 8 13 1024 863704
937 ( 8,112) | 78235 52847 1.5 | 8 11 1024 625880
938 ( 65,128) | 104631 63106 1.7 | 8 13 1024 837048
939 ( 66, 64) | 86365 50956 1.7 | 8 13 1024 690920
940 ( 66, 0) | 90413 46722 1.9 | 8 15 1024 723304
941 ( 66, 48) | 106631 65219 1.6 | 8 13 1024 853048
942 ( 8,192) | 80591 47154 1.7 | 8 13 1024 644728
943 ( 67, 16) | 72314 48487 1.5 | 8 11 1024 578512
944 ( 66, 96) | 90990 54454 1.7 | 8 13 1024 727920
945 ( 8, 96) | 110805 73522 1.5 | 8 12 1024 886440
946 ( 8, 80) | 85032 56643 1.5 | 8 12 1024 680400
947 ( 8, 48) | 87374 57544 1.5 | 8 12 1024 698992
948 ( 67, 0) | 79611 53515 1.5 | 8 11 1024 636888
949 ---------- | -------- -------- ------- | -------- -------- -------- --------
950 DEV | #Q #D Ratio | BLKmin BLKavg BLKmax Total
951 TOTAL | 4485736 2790572 1.6 | 8 12 1024 35896640
954 \newpage\begin{verbatim}
956 ==================== Device Seek Information ====================
958 DEV | NSEEKS MEAN MEDIAN | MODE
959 ---------- | --------------- --------------- --------------- | ---------------
960 ( 8,160) | 47890 203945.5 0 | 0(2496)
961 ( 8,176) | 55492 252948.8 0 | 0(2360)
962 ( 8,208) | 63944 167845.3 0 | 0(4327)
963 ( 65, 32) | 44494 224708.3 0 | 0(2683)
964 ( 65, 64) | 77396 197838.0 0 | 0(2532)
965 ( 65,176) | 62746 168400.5 0 | 0(2675)
966 ( 65, 96) | 51705 162500.2 0 | 0(2778)
967 ( 8,224) | 49753 206665.7 0 | 0(2753)
968 ( 65,112) | 63530 146289.8 0 | 0(2598)
969 ( 8,240) | 44700 167258.3 0 | 0(2735)
970 ( 65,192) | 59010 217004.7 0 | 0(2724)
971 ( 65,240) | 53548 278194.8 0 | 0(2415)
972 ( 65, 48) | 44652 180710.3 0 | 0(2660)
973 ( 8, 32) | 63116 234049.5 0 | 0(2473)
974 ( 66, 80) | 71526 184981.9 0 | 0(2455)
975 ( 66, 32) | 53134 198369.5 0 | 0(2415)
976 ( 65,224) | 66180 157948.5 0 | 0(2859)
977 ( 65,144) | 70205 195689.7 0 | 0(2734)
978 ( 8,144) | 49047 169282.7 0 | 0(2574)
979 ( 66,144) | 70613 149265.7 0 | 0(2717)
980 ( 66,128) | 65381 165931.1 0 | 0(2687)
981 ( 66,176) | 47894 199744.8 0 | 0(3096)
982 ( 66,224) | 58159 161603.9 0 | 0(2738)
983 ( 66,192) | 55417 153055.3 0 | 0(2828)
984 ( 66,160) | 71156 126479.4 0 | 0(2739)
985 ( 66,240) | 66472 142014.0 0 | 0(2933)
986 ( 66,112) | 82027 115471.3 0 | 0(2961)
987 ( 8, 64) | 63892 136632.0 0 | 0(2655)
988 ( 65,160) | 55579 154668.3 0 | 0(3377)
989 ( 65,208) | 67987 152829.1 0 | 0(2523)
990 ( 66, 16) | 56613 150652.8 0 | 0(2886)
991 ( 65, 0) | 51532 186889.7 0 | 0(2765)
992 ( 65, 16) | 35982 327187.6 0 | 0(2756)
993 ( 66,208) | 54306 243784.1 0 | 0(3076)
994 ( 8,128) | 59653 170797.2 0 | 0(2800)
995 ( 65, 80) | 65672 224501.4 0 | 0(2452)
996 ( 8,112) | 52847 213100.3 0 | 0(2417)
997 ( 65,128) | 63106 207821.8 0 | 0(2686)
998 ( 66, 64) | 50956 198045.0 0 | 0(2896)
999 ( 66, 0) | 46722 205476.3 0 | 0(3159)
1000 ( 66, 48) | 65219 142716.6 0 | 0(2869)
1001 ( 8,192) | 47154 248778.6 0 | 0(2584)
1002 ( 67, 16) | 48487 193335.5 0 | 0(2879)
1003 ( 66, 96) | 54454 185100.7 0 | 0(2158)
1004 ( 8, 96) | 73522 216187.1 0 | 0(2476)
1005 ( 8, 80) | 56643 172561.8 0 | 0(2612)
1006 ( 8, 48) | 57544 219104.1 0 | 0(2472)
1007 ( 67, 0) | 53515 161613.8 0 | 0(2990)
1008 ---------- | --------------- --------------- --------------- | ---------------
1009 Overall | NSEEKS MEAN MEDIAN | MODE
1010 Average | 2790572 185170.0 0 | 0(131433)
1013 \newpage\begin{verbatim}
1014 ==================== Plug Information ====================
1016 DEV | # Plugs # Timer Us | % Time Q Plugged
1017 ---------- | ---------- ---------- | ----------------
1018 ( 8,160) | 45092( 0) | 0.003021834%
1019 ( 8,176) | 49430( 0) | 0.003724997%
1020 ( 8,208) | 58950( 0) | 0.004506453%
1021 ( 65, 32) | 41617( 0) | 0.002710008%
1022 ( 65, 64) | 74294( 0) | 0.004971739%
1023 ( 65,176) | 59764( 0) | 0.003827258%
1024 ( 65, 96) | 47495( 0) | 0.004012641%
1025 ( 8,224) | 46806( 0) | 0.003724031%
1026 ( 65,112) | 60539( 0) | 0.004272802%
1027 ( 8,240) | 41797( 0) | 0.002832794%
1028 ( 65,192) | 54754( 0) | 0.004049758%
1029 ( 65,240) | 50757( 0) | 0.003466684%
1030 ( 65, 48) | 41749( 0) | 0.002783118%
1031 ( 8, 32) | 59486( 0) | 0.004102902%
1032 ( 66, 80) | 67519( 0) | 0.004698104%
1033 ( 66, 32) | 50441( 0) | 0.003229586%
1034 ( 65,224) | 60219( 0) | 0.005114778%
1035 ( 65,144) | 64699( 0) | 0.005185315%
1036 ( 8,144) | 46237( 0) | 0.002824578%
1037 ( 66,144) | 67605( 0) | 0.004459997%
1038 ( 66,128) | 62418( 0) | 0.004598612%
1039 ( 66,176) | 43007( 0) | 0.003277143%
1040 ( 66,224) | 54724( 0) | 0.003682546%
1041 ( 66,192) | 52395( 0) | 0.003611178%
1042 ( 66,160) | 67775( 0) | 0.004347445%
1043 ( 66,240) | 62892( 0) | 0.003906526%
1044 ( 66,112) | 72351( 0) | 0.005906198%
1045 ( 8, 64) | 59642( 0) | 0.004275726%
1046 ( 65,160) | 50303( 0) | 0.003841735%
1047 ( 65,208) | 64750( 0) | 0.004655374%
1048 ( 66, 16) | 53443( 0) | 0.003936557%
1049 ( 65, 0) | 48450( 0) | 0.003301599%
1050 ( 65, 16) | 33047( 0) | 0.002447028%
1051 ( 66,208) | 51060( 0) | 0.003674090%
1052 ( 8,128) | 52664( 0) | 0.004009472%
1053 ( 65, 80) | 61974( 0) | 0.004623080%
1054 ( 8,112) | 50106( 0) | 0.003284028%
1055 ( 65,128) | 60047( 0) | 0.004267589%
1056 ( 66, 64) | 47590( 0) | 0.003646022%
1057 ( 66, 0) | 43413( 0) | 0.003600655%
1058 ( 66, 48) | 61984( 0) | 0.004440717%
1059 ( 8,192) | 44294( 0) | 0.003120507%
1060 ( 67, 16) | 45482( 0) | 0.002852274%
1061 ( 66, 96) | 50099( 0) | 0.003970858%
1062 ( 8, 96) | 70266( 0) | 0.004743310%
1063 ( 8, 80) | 53676( 0) | 0.003530690%
1064 ( 8, 48) | 54672( 0) | 0.003527266%
1065 ( 67, 0) | 50418( 0) | 0.003217817%
1066 ---------- | ---------- ---------- | ----------------
1067 DEV | # Plugs # Timer Us | % Time Q Plugged
1068 OVERALL | 54420( 0) | 0.003871155%