summaryrefslogtreecommitdiff
path: root/btt/doc/btt.tex
blob: a3d190bb9b743bc71d4873bd4cc9203ece7d2af7 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
\documentclass{article}
\usepackage{epsfig,placeins}

%
% Copyright (C) 2007-2009 Alan D. Brunelle <Alan.Brunelle@hp.com>
%
%  This program is free software; you can redistribute it and/or modify
%  it under the terms of the GNU General Public License as published by
%  the Free Software Foundation; either version 2 of the License, or
%  (at your option) any later version.
%
%  This program is distributed in the hope that it will be useful,
%  but WITHOUT ANY WARRANTY; without even the implied warranty of
%  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
%  GNU General Public License for more details.
%
%  You should have received a copy of the GNU General Public License
%  along with this program; if not, write to the Free Software
%  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
%
%  vi :set textwidth=75

\title{\texttt{btt} User Guide}
\author{Alan D. Brunelle (Alan.Brunelle@hp.com)}
\date{8 October 2009}

\begin{document}
\maketitle
%--------------
\section{\label{sec:intro}Introduction}

\texttt{btt} is a post-processing tool for the block layer IO tracing
tool called blktrace. As noted in its Users Guide, blktrace

  \begin{quotation}
    is a block layer IO tracing mechanism which provides detailed
    information about request queue operations up to user space.
  \end{quotation}

blktrace is capable of producing tremendous amounts of output in the
form of multiple individual traces per IO executed during the traced
run. It is also capable of producing some general statistics concerning
IO rates and the like. \texttt{btt} goes further and produces a variety
of overall statistics about each of the individual handling of IOs, and
provides data we believe is useful to plot to provide visual comparisons
for evaluation.

This document will discuss \texttt{btt} usage, provide some sample output,
and also show some interesting plots generated from the data provided
by the \texttt{btt} utility.

\bigskip
A short note on the ordering of this document -- the actual
command-line usage section occurs relatively late in the document (see
section~\ref{sec:cmd-line}), as we felt that discussing some of the
capabilities and output formats would make the parameter discussion
easier.

\bigskip
  This document refers to the output formats generated by \texttt{btt}
  version 2.00.  However, the descriptions are general enough to cover
  output formats prior to that.

\newpage\tableofcontents

\newpage\section{\label{sec:getting-started}Getting Started}

  The simple pipeline to get going with \texttt{btt} is to perform the
  following steps:

  \begin{enumerate}
    \item Run \texttt{blktrace}, specifying whatever devices and other
    parameters you want. You must save the traces to disk in this step,
    btt does not work in live mode.

    \item After tracing completes, run \texttt{blkrawverify}, specifying
    all devices that were traced (or at least on all devices that you
    will use \texttt{btt} with -- section~\ref{sec:o-D} shows how you
    can dictate which devices to use with btt). If blkrawverify finds
    errors in the trace streams saved, it is best to recapture the data
    -- utilizing \texttt{btt} on \emph{unclean} trace files produces
    inconsistent results.

    While this step is optional, we have found that performing this
    helps to ensure data coming from \texttt{btt} makes the most sense.

    \item Run \texttt{blkparse} with the \texttt{-d} option specifying
    a file to store the combined binary stream. (e.g.: \texttt{blkparse
    -d bp.bin ...}).

    \texttt{blktrace} produces a series of binary files
    containing parallel trace streams -- one file per CPU per
    device. \texttt{blkparse} provides the ability to combine all the
    files into one time-ordered stream of traces for all devices.

    \item Run \texttt{btt} specifying the file produced by
    \texttt{blkparse} utilizing the \texttt{-i} option (e.g.: \texttt{btt
    -i bp.bin ...}).

  \end{enumerate}

\newpage\section{\label{sec:output-overview}Output Overview}

  The major default areas of output provided by \texttt{btt}
  include\label{tl-defs}:

\begin{description}
  \item[average component times across all IOs] The time line of each IO
  is broken down into 3 major regions:

    \begin{enumerate}
      \item Time needed to insert or merge an incoming IO onto the request
      queue. This is the average time from when the IO enters the block
      IO layer (queue trace) until it is inserted (insert trace).

      This is denoted as \emph{Q2I} time.

      This is also broken down into two component times\footnote{On
      occasion there are also some time spent \emph{sleeping} waiting
      for a request. That occurs between the Q and G operations. You
      will see these listed as \texttt{S2G} times.}:

        \begin{description}
	  \item[Q2G] Time needed to \emph{get} a request (get request
	  trace).

	  \item[G2I] Time needed to put that request onto the request
	  queue (insert trace).
        \end{description}

      For \emph{merged} requests -- an incoming request that is merged
      with a previously submitted request -- we calculate \emph{Q2M}, the
      amount of time between the queue trace and the merge trace.

      \item Time spent on the request queue. The average time from when
      the IO is inserted or merged onto the request queue, until it is
      issued (issue trace) to the lower level driver.

      Referred to as \emph{I2D} time\footnote{The \emph{issue} trace
      is represented by a D in the blkparse output, hence its usage in
      btt to refer to issue traces. Note that an I is used to refer to
      \emph{insert} traces.}.

      \item Driver and device time -- the average time from when the
      actual IO was issued to the driver until is completed (completion
      trace) back to the block IO layer.

      This is referred to as the \emph{D2C} time\
    \end{enumerate}

  Two other sets of results are presented in this section:

    \begin{enumerate}
      \item \emph{Q2Q} which measures the time between queue traces
      in the system. This provides some idea as to how quickly IOs are
      being handed to the block IO layer.

      \item \emph{Q2C} which measures the times for the complete life cycle
      of IOs during the run\footnote{One of the areas that needs some
      work in \texttt{btt} is to better understand the multiplex nature of
      IOs during a run. In theory, one would like ${Q2I} + {I2D} + {D2C}
      = {Q2C}$ however, typically there are multiple queue traces that
      are combined via merges into a single IO issued and completed. We
      currently average the queue-to-insert and queue-to-merge times,
      and thus tend to be quite close to the expected equation.}

    \end{enumerate}

  For each row in this output, we provide a minimum, average, maximum
  (which are all presented in seconds), and overall count. As an
  example\footnote{As with this display, the author has taken some liberty
  in reformatting the output for better display on the printed page.}:

\begin{verbatim}
ALL            MIN           AVG           MAX           N
---- ------------- ------------- ------------- -----------
Q2Q    0.000000058   0.000012761   9.547941661     2262310
Q2I    0.000000272   0.000005995   0.104588839     2262311
I2D    0.000001446   0.094992714   0.239636864     2262311
D2C    0.000193721   0.030406554   1.634221408     2262311
Q2C    0.000207665   0.125405263   1.830917198     2262311
\end{verbatim}

  When tracking \emph{device mapper} devices, we also break down the
  \emph{Q2A} and \emph{Q2C} times for those IOs.

  \item[Device Overhead]

  Using the data from the previous chart, we can then provide some idea
  as to where IO spend most of the time on average. The following output
  shows the percentage of time spent in each of the phases of an
IO\footnote{It should be noted that incoming requests either go through:

\begin{enumerate}
  \item Q2G + Q2I

  or

  \item Q2M
\end{enumerate}
  before proceeding to I2D and D2C.}

\begin{verbatim}
       DEV |       Q2G       G2I       Q2M       I2D       D2C
---------- | --------- --------- --------- --------- ---------
 (  8, 80) |   0.0013%   0.0004%   0.0006%  88.5005%  11.4988%
---------- | --------- --------- --------- --------- ---------
   Overall |   0.0003%   0.0001%   0.0041%  21.4998%  78.4958%
\end{verbatim}

  \item[Device Merge Information]

  A key measurement when making changes in the system (software \emph{or}
  hardware) is to understand the block IO layer ends up merging incoming
  requests into fewer, but larger, IOs to the underlying driver. In this
  section, we show the number of incoming requests (Q), the number of
  issued requests (D) and the resultant ratio. We also provide values
  for the minimum, average and maximum IOs generated.

  Looking at the following example:

\begin{verbatim}
       DEV |      #Q    #D Ratio | BLKmin BLKavg BLKmax   Total
---------- | ------- ----- ----- | ------ ------ ------ -------
 ( 68, 64) | 2262311 18178 124.5 |      2    124    128 2262382
\end{verbatim}

  we see that (on average) the block IO layer is combining upwards of
  125 incoming requests into a single request down the IO stack. The
  resultant average IO size is 124 blocks.

  \item[Device Seek Information]

  Another useful measure is the variability in the sector distances
  between consecutively \emph{received -- queued} and \emph{submitted
  -- issued} IOs. The next two sections provides some rudimentary
  statistics to gauge the general nature of the sector differences
  between IOs. Values provided include the number of seeks (number of IOs
  submitted to lower level drivers), the \emph{mean} distance between
  IOs, the \emph{median} value for all seeks, and the \emph{mode} -
  the value(s) and the counts are provided for the latter.

  The first of the two sections displays values for Q2Q seek distances --
  providing a set of indicators showing how close incoming IO requests
  are to each other. The second section shows D2D seek distances --
  providing a set of indicators showing how close the IO requests are
  that are handled by underlying drivers.

\begin{verbatim}
      DEV | NSEEKS    MEAN MEDIAN | MODE
--------- | ------ ------- ------ | -------
( 68, 64) |  18178 19611.3      0 | 0(17522)
\end{verbatim}

  We have almost exclusively seen median and mode values of 0, indicating
  that seeks tend to have an equal amount of forward and backwards
  seeks. The larger the count for the mode in comparison to the total
  number of seeks is indicative as to how many IOs are coming out of
  the block IO layer in adjacent sectors. (Obviously, the higher this
  percentage, the better the underlying subsystems can handle them.)

  \item[Request Queue Plug Information]

  During normal operation, requests queues are \emph{plugged} and during
  such times the IO request queue elements are not able to be processed
  by underlying drivers. The next section shows how often the request
  queue was in such a state.

\begin{verbatim}
      DEV | # Plugs # Timer Us  | % Time Q Plugged
--------- | ------- ----------  | ----------------
( 68, 64) |     833(         0) |   0.356511895%
\end{verbatim}

  There are two major reasons why request queues are unplugged, and both
  are represented in the above table.

  \begin{enumerate}
    \item Explicit unplug request from some subsystem in the kernel.

    \item Timed unplugs, due to a request queue exceeding some temporal
    limit for being plugged.
  \end{enumerate}

  The total number of unplugs is equal to the number of plugs less the
  ones due to timer unplugs.

  \item[IOs per Unplug \& Unplugs-due-to-timeout]

  In this subsection one can see the average number of IOs on the request
  queue at the time of an unplug or unplug due to a timeout. The following
  sample shows a sample of both unplug sections:

\begin{verbatim}
==================== Plug Information ====================

       DEV |    # Plugs # Timer Us  | % Time Q Plugged
---------- | ---------- ----------  | ----------------
 (  8,  0) |       1171(       123) |   0.280946640%
 (  8, 32) |          4(         0) |   0.000325469%
---------- | ---------- ----------  | ----------------
   Overall |    # Plugs # Timer Us  | % Time Q Plugged
   Average |        587(        61) |   0.140636055%

       DEV |    IOs/Unp   IOs/Unp(to)
---------- | ----------   ----------
 (  8,  0) |        9.2          8.8
 (  8, 32) |        2.5          0.0
---------- | ----------   ----------
       DEV |    IOs/Unp   IOs/Unp(to)
   Overall |        9.2          8.8
\end{verbatim}

  This table and the preceding one have to be considered together --
  in the sample output in the immediately preceding table one can see
  how the larger number of data values for device (8,0) dominates in
  the overall average.

  \newpage\item[Active Requests At Q Information]

  An important consideration when analyzing block IO schedulers is to
  know how many requests the scheduler has to work with. The metric
  provided in this section details how many requests (on average) were
  being held by the IO scheduler when an incoming IO request was being
  handled. To determine this, \texttt{btt} keeps track of how many Q
  requests came in, and subtracts requests that have been issued (D).

  Here is a sample output of this sections:

\begin{verbatim}
==================== Active Requests At Q Information ====================

       DEV |  Avg Reqs @ Q
---------- | -------------
 ( 65, 80) |          12.0
 ( 65,240) |          16.9
...
 ( 66,112) |          44.2
---------- | -------------
   Overall | Avgs Reqs @ Q
   Average |          17.4
\end{verbatim}

  \item[I/O Active Period Information]

  In this subsection data is tabulated showing I/O activity on a
  per-device as well across all devices being traced. ``I/O activity''
  is defined as periods of time when the underlying device driver and
  device have at least one I/O to work upon. The values presented include:

  \begin{description}
    \item[\# Live] Number of periods of ``liveness.''
    \item[Avg. Act] Average length of each period ov ``liveness.''
    \item[Avg. !Act] Aerage length of each non-active period.
    \item[\% Live] Percent of total time spent with the driver/device active.
  \end{description}

  Here is a sample portion of this type of chart:

\begin{verbatim}
       DEV |     # Live      Avg. Act     Avg. !Act % Live
---------- | ---------- ------------- ------------- ------
 (  8, 16) |         29   0.909596815   0.094646263  90.87
 (  8, 32) |        168   0.097848226   0.068231948  59.06
---------- | ---------- ------------- ------------- ------
 Total Sys |         33   0.799808811   0.082334758  90.92
\end{verbatim}

  For information on generating data files that can be plotted with
  per-device and system-wide I/O activity see section~\ref{sec:o-Z}.

\end{description}

\newpage
\subsection*{\label{sec:detailed-data}Detailed Data}

  In addition to the default sections output, if one supplies the
  \texttt{--all-data} or \texttt{-A} argument (see section~\ref{sec:o-A})
  to \texttt{btt} further sections are output:

\begin{description}
  \item[Per Process] As traces are emitted, they are tagged with the
  process ID of the currently running thread in the kernel. The process
  names are also preserved, and mapped to the ID. For each of the parts
  of the time line discussed above on page~\pageref{tl-defs}, a chart is
  provided which breaks down the traces according to process ID (name).

  One must be aware, however, that the process ID may not have anything
  to do with the originating IO. For example, if an application is
  doing buffered IO, then the actual submitted IOs will most likely
  come from some page buffer management daemon thread (like pdflush,
  or kjournald for example). Similarly, completion traces are rarely
  (if ever?) going to be associated with the process which submitted
  the IO in the first place.

  Here is a sample portion of this type of chart, showing Q2Q times
  per process:

\begin{verbatim}
          Q2Q         MIN         AVG         MAX       N
------------- ----------- ----------- ----------- -------
mkfs.ext3     0.000000778 0.000009074 1.797176188 1899371
mount         0.000000885 0.000672513 0.030638128      73
pdflush       0.000000790 0.000006752 0.247231307  179791
\end{verbatim}

  \item[Per Process Averages] The average columns from the above charts,
  are also presented in their own chart.

  \item[Per Device] Similar to the per-process display, \texttt{btt}
  will also break down the various parts of an IOs time line based upon a
  per-device criteria. Here's a portion of this area, displayed showing
  the issued to complete times (D2C).

\begin{verbatim}
      D2C         MIN         AVG         MAX      N
--------- ----------- ----------- ----------- ------
( 65, 80) 0.000140488 0.001076906 0.149739869 169112
( 65, 96) 0.000142762 0.001215221 0.173263182 155488
( 65,112) 0.000145221 0.001254966 0.124929936 165726
( 65,128) 0.000141896 0.001159596 0.775231052 169015
( 65,144) 0.000140832 0.001290985 0.211384698 210661
( 65,160) 0.000139915 0.001175554 0.073512063 133973
( 65,176) 0.000141254 0.001104870 0.073231310 145764
( 65,192) 0.000141453 0.001234460 0.167622507 140618
...
\end{verbatim}

  \item[Per Device Averages] The average columns from the above charts,
  are also presented in their own chart.

  \item[Q2D Histogram] A display of histogram buckets for the Q to D times
  -- basically, from where an IO enters the block IO layer for a given
  device, and when it is dispatched. The buckets are arranged via the
  time in seconds, as in:

\begin{verbatim}
==================== Q2D Histogram ====================

       DEV | <.005 <.010 <.025 <.050 <.075 <.100 <.250 <.500 < 1.0 >=1.0
 --------- | ===== ===== ===== ===== ===== ===== ===== ===== ===== =====
 ( 66, 80) |  61.2   7.9  12.1   7.9   3.0   1.4   1.5   0.2   0.0   4.6
 ( 65,192) |  42.3   5.0   8.7  30.0   8.9   3.0   1.8   0.1   0.0   0.1
 ( 65,128) |  34.3   5.3   8.9  32.0   9.7   3.7   5.3   0.6   0.0   0.1
...
 ( 65, 64) |  59.9   4.2   6.0  24.6   4.2   0.8   0.1   0.0   0.0   0.1
 ( 66, 64) |  62.6   8.1  12.7   7.9   2.4   0.6   0.1   0.0   0.0   5.4
========== | ===== ===== ===== ===== ===== ===== ===== ===== ===== =====
       AVG |  52.9   6.2  10.0  20.1   5.3   1.7   1.4   0.2   0.0   2.1
\end{verbatim}

\end{description}

\newpage\section{\label{sec:data-files}Data Files Output}

  Besides the averages output by default, the following 5(+) files are also
  created with data points which may be plotted.

\begin{description}
  \item[\emph{file}.dat] This file provides a notion of \emph{activity}
  for the system, devices and processes. The details of this file are
  provided in section~\ref{sec:activity}.

  \item[\emph{file}\_qhist.dat] Provides histogram data for the size of
  incoming IO requests, for more information see section~\ref{sec:qhist}.

  \item[\emph{file}\_dhist.dat] Provides histogram data for the size
  of IO requests submitted to lower layer drivers, for more information
  see section~\ref{sec:dhist}.

  \item[\emph{file}\_mbps\_fp.dat] Provides a set of data for
  mb-per-second values each second
  - for more information see section~\ref{sec:rstat}.

  \item[\emph{file}\_iops\_fp.dat] Provides a set of data for
  I/Os-per-second values each second
  - for more information see section~\ref{sec:rstat}.

\end{description}

  In addition to the default data files output, there are optional data
  files which can be generated by btt. These include:

  \begin{description}
    \item[subset of \texttt{.avg} data, easily parsed ] When the
    \texttt{-X} option is specified \emph{and} the \texttt{-o} has also
    been specified, then a subset of the data produced by default is
    copied to another file that is \emph{more easily parsed.} Refer to
    section~\ref{sec:o-X} for full details.

    \item[iostat] iostat-like data can be distilled by btt, and is
    described in section~\ref{sec:iostat}.

    \item[per IO detail] Each and every IO traced can be output in a form
    that shows each of the IO components on consecutive lines (rather
    than grepping through a blkparse output file for example). The
    details on this file is included in section~\ref{sec:per-io}.

    \item[iostat] Latency information -- both Q2d, D2c and Q2C --
    on a per-IO basis can be generated. These are described in
    section~\ref{sec:lat}.

    \item[seek details] A set of data files containing all IO-to-IO
    sector differences can be output, with details found in
    section~\ref{sec:seek}.

    \item[unplug histogram details] A data file per device containing
    histogram output for the amount of IOs released at unplug time.
    Section~\ref{sec:o-u} has more details.
  \end{description}

\newpage\section{\label{sec:activity}Activity Data File}

  The activity data file contains a series of data values that indicate
  those periods of time when queue and complete traces are being
  processed.  The values happen to be in a format easily handled by
  xmgrace\footnote{\texttt{http://plasma-gate.weizmann.ac.il/Grace/}
  ``Grace is a WYSIWYG 2D plotting tool for the X Window System and
  M*tif.''}, but is easy to parse for other plotting and/or analysis
  programs.

  The file is split into pairs of sets of data points, where each pair
  contains a set of queue activity and a set of completion activity. The
  points are presented with the first column (X values) being the time
  (in seconds), and the second column (Y values) providing an on/off
  type of setting. For each pair, the Y values have two settings off
  (low) and on (high). For example, here is a snippet of a file showing
  some Q activity:

\begin{verbatim}
# Total System
#     Total System : q activity
0.000000000   0.0
0.000000000   0.4
0.000070381   0.4
0.000070381   0.0
1.023482637   0.0
1.023482637   0.4
6.998746618   0.4
6.998746618   0.0
7.103336799   0.0
7.103336799   0.4
17.235419786   0.4
17.235419786   0.0
26.783361447   0.0
26.783361447   0.4
26.832454929   0.4
26.832454929   0.0
28.870431266   0.0
28.870431266   0.4
28.870431266   0.4
28.870431266   0.0
\end{verbatim}

  What this indicates is that there was q activity for the system
  from 0.000000000 through 0.000070381, but was inactive from there to
  1.023482637, and so on. Section~\ref{sec:o-d} contains details on how
  to adjust btt's notion of what constitutes activity.

  The pairs are arranged as follows:

  \begin{itemize}
    \item First there is the total system activity -- meaning activity
    in either queue or completion traces across all devices.

    \item Next comes per-device activity information -- for each device
    being traced, that request queues Q and C traces are presented.

    \item Last we present pairs per-process.
  \end{itemize}

  Using this, one is then able to plot regions of activity versus
  inactivity -- and one can gather a sense of deltas between the queueing
  of IOs and when they are completed. Figure~\ref{fig:activity} shows
  a very simplistic chart showing some activity:

  \begin{figure}[hb]
  \leavevmode\centering
  \epsfig{file=activity.eps,width=4.5in}
  \caption{\label{fig:activity}Simple Activity Chart}
  \end{figure}

  When the black line (system Q activity) is \emph{high}, then the system
  is seeing relatively continuous incoming queues. Conversely, when it is
  low, it represents an extended period of time where no queue requests
  were coming in. Similarly for the red line and C activity.

\newpage\section{\label{sec:hist}Histogram Data Files}

  The histogram data files provide information concerning incoming and
  outgoing IO sizes (in blocks). For simplicity, the histogram buckets
  are one-for-one for sizes up to 1,024 blocks in the IO, and then a
  single bucket for all sizes greater than or equal to 1,024 blocks.

  The files are again in grace-friendly format, with the first set
  containing data for the first 1,023 buckets, and a separate set
  representing sizes $\ge 1024$ blocks. (This is done so that one can
  easily use a separate formatting specification for the latter set.)

  The first column (X values) is the various IO sizes, and the second
  column (Y values) represents the number of IOs of that size.

\subsection*{\label{sec:qhist}Q Histogram Data File}

  Figure~\ref{fig:qhist} is a sample graph generated from data used during
  some real-world analysis\footnote{Note the logarithmic nature of the
  Y axis for this chart.}. With the visual representation provided by
  this, one can quickly discern some different characteristics between
  the 3 runs -- in particular, one can see that there is only a single
  red point (representing 8 blocks per IO), whereas the other two had
  multiple data points greater than 8 blocks.

  \begin{figure}[hb]
  \leavevmode\centering
  \epsfig{file=qhist.eps,width=4.5in}
  \caption{\label{fig:qhist}Q Histogram}
  \end{figure}

\subsection*{\label{sec:dhist}D Histogram Data File}

  Figure~\ref{fig:dhist} is a sample graph generated from data used during
  some real-world analysis\footnote{Note the logarithmic nature of the
  Y axis for this chart.}. Again, visually, one can see that the black
  and blue dots are somewhat similar below about 192 blocks per IO going
  out. And then one can make the broad generalization of higher reds,
  lower blues and blacks in the middle.

  \begin{figure}[hb]
  \leavevmode\centering
  \epsfig{file=dhist.eps,width=4.5in}
  \caption{\label{fig:dhist}D Histogram}
  \end{figure}

\newpage\section{\label{sec:rstat}Running Stats Files}

There are two files produced for each of all devices being traced
(prefixed with \emph{sys\_}) and per-device (prefixed with the device
identifier).

The two files are for reporting I/O rate (I/Os per second - name ends
with \texttt{iops\_fp.dat}) and throughput (MiB per second - name ends
with \texttt{mbps\_fp.dat}).

The data in the files has two columns:\smallskip

\begin{tabular}{lll}
\textbf{File Type} & \textbf{X values} & \textbf{Y values}\\\hline
\textbf{iops} & Runtime (seconds) & I/Os per second\\\hline
\textbf{mbps} & Runtime (seconds) & MiB per second\\\hline
\end{tabular}

As an example:

\begin{verbatim}
# ls *fp.dat
008,064_iops_fp.dat
008,064_mbps_fp.dat
sys_iops_fp.dat
sys_mbps_fp.dat
\end{verbatim}

These can be plotted using various tools (e.g., xmgrace as in
figure~\ref{fig:rstats}).

  \begin{figure}[b!]
  \leavevmode\centering
  \epsfig{file=rstats.eps,width=4.5in}
  \caption{\label{fig:rstats}Running Stats}
  \end{figure}

\newpage\section{\label{sec:iostat}iostat Data File}
  \texttt{btt} attempts to produce the results from running an
  \texttt{iostat -x} command in parallel with the system as it is being
  traced. The fields (columns) generated by the \texttt{--iostat} or
  \texttt{-I} option can be seen from the following output snippet --
  note that the line has been split to fit on the printed page:

\begin{verbatim}
Device:       rrqm/s   wrqm/s     r/s     w/s    rsec/s    wsec/s
             rkB/s     wkB/s avgrq-sz avgqu-sz   await   svctm  %util   Stamp
...
(  8, 16)       0.00     0.00    0.00 1005.30      0.00 152806.36     
              0.00  76403.18   152.00    31.00    0.00    0.00   0.00   71.79
...
(  8, 16)       1.02     5.80    0.34    1.07      4.03     55.62
              2.02     27.81    42.13     0.61    0.00   21.90   0.00   TOTAL
\end{verbatim}

  Note that the STAMP field contains the runtime (in seconds) for that
  line of data.

\newpage\section{\label{sec:per-io}Per-IO Data File}

  \texttt{btt} can produce a text file containing time line data for each
  IO processed. The time line data contains rudimentary information for
  the following stages:

  \begin{itemize}
    \item queue traces
    \item get request traces
    \item insert traces
    \item merge traces
    \item issue traces
    \item completion traces
    \item remap traces
  \end{itemize}

  The \emph{--per-io-dump} or \emph{-p} option triggers this behavior,
  and will produce a file containing streams of IOs (separated by blank
  spaces). As an example, here is a snippet of 4 IOs that were merged
  together, you will note there are 3 merged IOs, and 1 inserted in the
  stream. The issue and completion traces are replicated per IO.

\begin{verbatim}
 66,0  :     0.763283556 Q       6208+8  
             0.763300157 I       6208+8  
             0.763296365 G       6208+8  
             0.763338848 D       6208+32 
             0.763705760 C       6208+32 

 66,0  :     0.763314550 Q       6224+8  
             0.763315341 M       6224+8  
             0.763338848 D       6208+32 
             0.763705760 C       6208+32 

 66,0  :     0.763321010 Q       6232+8  
             0.763321775 M       6232+8  
             0.763338848 D       6208+32 
             0.763705760 C       6208+32 

 65,240:     0.763244173 Q       6216+8  
             0.763244974 M       6216+8  
             0.763374288 D       6208+32 
             0.763826610 C       6208+32 
\end{verbatim}

  The columns provide the following information:

  \begin{enumerate}
    \item Device major/minor.

    \item Time of the trace (seconds from the start of the run)

    \item Trace type

    \item start block + number of blocks
  \end{enumerate}
 
\newpage\section{\label{sec:lat}\label{sec:lat-q2d}\label{sec:lat-q2c}\label{sec:lat-d2c}Latency Data Files}

  The latency data files which can be optionally produced by \texttt{btt}
  provide per-IO latency information, one for queue time (Q2D), one
  for total IO time (Q2C) and one for latencies induced by lower layer
  drivers and devices (D2C).

  In both cases, the first column (X values) represent runtime (seconds),
  while the second column (Y values) shows the actual latency for a
  command at that time (either Q2D, D2C or Q2C).

\newpage\section{\label{sec:seek}Seek Data Files}

  \texttt{btt} can also produce two data files containing all IO-to-IO sector
  deltas, providing seek information which can then be plotted. The
  produced data file contains 3 sets of data:

  \begin{enumerate}
     \item Combined data -- all read and write IOs

     \item Read data -- just seek deltas for reads

     \item Write data -- just seek deltas for writes
  \end{enumerate}

  The format of the output file names is to have the name generated by
  the following fields separated by underscores (\texttt{\_}):
 
  \begin{itemize}
    \item The prefix provided as the argument to the \texttt{-s} option.
    \item The major and minor numbers of the device separated by a comma.
    \item The string \texttt{q2q} or \texttt{d2d}, indicating the Q2Q or
          D2D seeks, respectively.
    \item One of the following characters:
    	\begin{description}
	  \item[r] For read (device to system) IOs
	  \item[w] For write (system to device) IOs
	  \item[c] Combined -- both read and write IOs
	\end{description}
  \end{itemize}

  An example name would be after specifying \texttt{-s seek} would be:
  \texttt{seek\_065,048\_q2q\_w.dat}.

  The format of the data is to have the runtime values (seconds since
  the start of the run) in column 1 (X values); and the difference in
  sectors from the previous IO in column 2 (Y values). Here is a snippet
  of the first few items from a file:

\begin{verbatim}
# Combined
     0.000034733           35283790.0
     0.000106453           35283790.0
     0.005239009           35283950.0
     0.006968575           35283886.0
     0.007218709           35283694.0
     0.012145393           35283566.0
     0.014980835          -35848914.0
     0.024239323          -35848914.0
     0.024249402          -35848914.0
     0.025707095          -35849072.0
     ...
\end{verbatim}

  Figure~\ref{fig:seek} shows a simple graph that can be produced which
  provides visual details concerning seek patterns.

  \begin{figure}[h!]
  \leavevmode\centering
  \epsfig{file=seek.eps,width=4.5in}
  \caption{\label{fig:seek}Seek Chart}
  \end{figure}
  \FloatBarrier

  The seek difference is calculated in one of two ways:

  \begin{description}
    \item[default] By default, the seek distance is calculated as the
    \emph{closest} distance between the previous IO and this IO. The
    concept of \emph{closeness} means that it could either be the
    \emph{end} of the previous IO and the beginning of the next, or the
    end of this IO and the start of the next.

    \item[\texttt{-a}] If the \texttt{-a} or \texttt{--seek-absolute}
    option is specified, then the seek distance is simply the difference
    between the end of the previous IO and the start of this IO.
  \end{description}

\newpage\subsection{\label{sec:sps-spec}Seeks Per Second}

  When the \texttt{-m} option provides a name, Q2Q and/or D2D seeks
  will trigger \texttt{btt} to output seeks-per-second information. The
  first column will contain a time value (seconds), and the second column
  will indicate the number of seeks per second at that point.

  When there is only a single data point within a 1-second window,
  \texttt{btt} will just output the time value for the point, and the
  value 1.0 in the second column. If there is no perceived difference
  in the times present for the current sample, then the second columns
  value is the number of seeks present at that time.

  Otherwise, if $\alpha$ and $\Omega$ are the first and last times
  seen within a 1-second window, and $\nu$ are the number of seeks seen
  in that time frame, then:

  \begin{description}
    \item[column 1] Midway point in time for this span, or: \hfill$\alpha +
    {{(\Omega - \alpha)} / 2}$

    \item[column 2] Average seeks per second over this span, or: \hfill$\nu  /
    {(\Omega - \alpha)}$
  \end{description}

  Figure~\ref{fig:sps} shows a simple pair of graphs generated from
  \texttt{-m} output:

  \begin{figure}[h!]
  \leavevmode\centering
  \epsfig{file=sps.eps,width=4.5in}
  \caption{\label{fig:sps}Seeks-per-second Chart}
  \end{figure}
  \FloatBarrier

\newpage\section{\label{sec:cmd-line}Command Line}

\begin{verbatim}
Usage: btt 2.09
[ -a               | --seek-absolute ]
[ -A               | --all-data ]
[ -B <output name> | --dump-blocknos=<output name> ]
[ -d <seconds>     | --range-delta=<seconds> ]
[ -D <dev;...>     | --devices=<dev;...> ]
[ -e <exe,...>     | --exes=<exe,...>  ]
[ -h               | --help ]
[ -i <input name>  | --input-file=<input name> ]
[ -I <output name> | --iostat=<output name> ]
[ -l <output name> | --d2c-latencies=<output name> ]
[ -L <freq>        | --periodic-latencies=<freq> ]
[ -m <output name> | --seeks-per-second=<output name> ]
[ -M <dev map>     | --dev-maps=<dev map>
[ -o <output name> | --output-file=<output name> ]
[ -p <output name> | --per-io-dump=<output name> ]
[ -P <output name> | --per-io-trees=<output name> ]
[ -q <output name> | --q2c-latencies=<output name> ]
[ -Q <output name> | --active-queue-depth=<output name> ]
[ -r               | --no-remaps ]
[ -s <output name> | --seeks=<output name> ]
[ -S <interval>    | --iostat-interval=<interval> ]
[ -t <sec>         | --time-start=<sec> ]
[ -T <sec>         | --time-end=<sec> ]
[ -u <output name> | --unplug-hist=<output name> ]
[ -V               | --version ]
[ -v               | --verbose ]
[ -X               | --easy-parse-avgs ]
[ -z <output name> | --q2d-latencies=<output name> ]
[ -Z               | --do-active
\end{verbatim}

\subsection{\label{sec:o-a}\texttt{--seek-absolute}/\texttt{-a}}

  When specified on the command line, this directs btt to calculate
  seek distances based solely upon the ending block address of one IO,
  and the start of the next.  By default \texttt{btt} uses the concept
  of the closeness to either the beginning or end of the previous IO. See
  section~\ref{sec:seek} for more details about seek distances.

\subsection{\label{sec:o-A}\texttt{--all-data}/\texttt{-A}}

  Normally \texttt{btt} will not print out verbose information
  concerning per-process and per-device data (as outlined in
  section~\ref{sec:detailed-data}). If you desire that level of
  detail you can specify this option.

\subsection{\label{sec:o-B}\texttt{--dump-blocknos}/\texttt{-B}}

  This option will output absolute block numbers to three files prefixed
  by the specified output name:

  \begin{description}
    \item[\emph{prefix}\_\emph{device}\_r.dat] All read block numbers are
    output, first column is time (seconds), second is the block number,
    and the third column is the ending block number.

    \item[\emph{prefix}\_\emph{device}\_w.dat] All write block numbers are
    output, first column is time (seconds), second is the block number,
    and the third column is the ending block number.

    \item[\emph{prefix}\_\emph{device}\_c.dat] All block numbers (read
    and write) are output, first column is time (seconds), second is
    the block number, and the third column is the ending block number.
  \end{description}

\subsection{\label{sec:o-d}\texttt{--range-delta}/\texttt{-d}}

  Section~\ref{sec:activity} discussed how \texttt{btt} outputs a file
  containing Q and C activity, the notion of \emph{active} traces simply
  means that there are Q or C traces occurring within a certain period
  of each other. The default values is 0.1 seconds; with this option
  allowing one to change that granularity. The smaller the value, the
  more data points provided.

\subsection{\label{sec:o-D}\texttt{--devices}/\texttt{-D}}

  Normally, \texttt{btt} will produce data for all devices detected in
  the traces parsed. With this option, one can reduce the analysis to
  one or more devices provided in the string passed to this option. The
  device identifiers are the major and minor number of each device, and
  each device identifier is separated by a colon (:). A valid specifier
  for devices 8,0 and 8,8 would then be: \texttt{"8,0:8,8"}.

\subsection{\label{sec:o-e}\texttt{--exes}/\texttt{-e}}

  Likewise, \texttt{btt} will produce data for all processes (executables)
  found in the traces. With this option, one can specify which processes
  you want displayed in the output. The format of the string passed is
  a list of executable \emph{names} separated by commas (,). An example
  would be \texttt{"-e mkfs.ext3,mount"}.

\subsection{\label{sec:o-h}\texttt{--help}/\texttt{-h}}

  Prints out the simple help information, as seen at the top of
  section~\ref{sec:cmd-line}.

\subsection{\label{sec:o-i}\texttt{--input-file}/\texttt{-i}}

  Specifies the binary input file that \texttt{btt} will interpret traces
  in. See section~\ref{sec:getting-started} for information concerning
  binary trace files.

\subsection{\label{sec:o-I}\texttt{--iostat}/\texttt{-I}}

  This option triggers \texttt{btt} to generate iostat-like output to the
  file specified. Refer to section~\ref{sec:iostat} for more information
  on the output produced.

\subsection{\label{sec:o-l}\texttt{--d2c-latencies}/\texttt{-l}}

  This option instructs \texttt{btt} to generate the D2C latency file
  discussed in section~\ref{sec:lat-d2c}.

\subsection{\label{sec:o-L}\texttt{--periodic-latencies}/\texttt{-L}}

  When given a value greater than 0, this option will create two data
  files (q2c \& d2c) per device containing a periodic timestamp \&
  average latency over that period.

\subsection{\label{sec:o-m}\texttt{--seeks-per-second}\texttt{-m}}

  Tells \texttt{btt} to output seeks per second information.  Each device
  being measured can have up to 2 files output: One with Q2Q information
  and one with D2D seek information. Information on the output produced
  can be found in section~\ref{sec:sps-spec}.

  \begin{quote}
    \textbf{Note: This requires seek output to be selected -- see
    section~\ref{sec:seek}.}
  \end{quote}

\subsection{\label{sec:o-M}\texttt{--dev-maps}/\texttt{-M}}

  Internal option, still under construction.

\subsection{\label{sec:o-o}\texttt{--output-file}/\texttt{-o}}

  Normally \texttt{btt} sends the statistical output (covered in
  section~\ref{sec:output-overview}) to standard out, if you specify
  this option this data is redirected to the file specified.

\subsection{\label{sec:o-p}\texttt{--per-io-dump}/\texttt{-p}}

  This option tells \texttt{btt} to generate the per IO dump file as
  discussed in section~\ref{sec:per-io}.

\subsection{\label{sec:o-P}\texttt{--per-io-tress}/\texttt{-P}}

The \texttt{-P} option will generate a file that contains a list of all IO
"sequences" - showing only the Q, D \& C operation times. The D \& C
time values are separated from the Q time values with a vertical bar.

\subsection{\label{sec:o-q}\texttt{--q2c-latencies}/\texttt{-q}}

  This option instructs \texttt{btt} to generate the Q2C latency file
  discussed in section~\ref{sec:lat-q2c}.

\subsection{\label{sec:o-Q}\texttt{--active-queue-depth}/\texttt{-Q}}

  This option tells \texttt{btt} to generate a data file (using the given
  name as a base) which contains: A time stamp in the first column,
  and then the number of \emph{active} requests issued to the device
  driver. (The value is incremented when an \emph{issue} is performend,
  and decremented when a \emph{complete} is performed.

\subsection{\label{sec:o-r}\texttt{--no-remaps}/\texttt{-r}}

  Ignore remap traces; older kernels did not implement the full remap PDU.

\subsection{\label{sec:o-s}\texttt{--seeks}/\texttt{-s}}

  This option instructs \texttt{btt} to generate the seek data file
  discussed in section~\ref{sec:seek}.

\subsection{\label{sec:o-S}\texttt{--iostat-interval}/\texttt{-S}}

  The normal \texttt{iostat} command allows one to specify the snapshot
  interval, likewise, \texttt{btt} allows one to specify how many seconds
  between its generation of snapshots of the data via this option. Details
  about the iostat-like capabilities of \texttt{btt} may be found in
  section~\ref{sec:iostat}.

\subsection{\label{sec:o-tT}\texttt{--time-start}/\texttt{-t} and
\texttt{--time-end}/\texttt{T}}

  \begin{quote}
    \emph{This \texttt{btt} capability is still under construction, results are
    not always consistent at this point in time.}
  \end{quote}

  These options allow one to dictate to \texttt{btt} when to start and stop
  parsing of trace data in terms of seconds since the start of the run. The
  trace chosen will be between the start time (or 0.0 if not
  specified) and end time (or the end of the run) specified.

\subsection{\label{sec:o-u}\texttt{--unplug-hist}/\texttt{-u}}

  This option instructs \texttt{btt} to generate a data file containing
  histogram information for \emph{unplug} traces on a per device
  basis. It shows how many times an unplug was hit with a specified
  number of IOs released. There are 21 output values into the file, as
  follows:

  \medskip
  \begin{tabular}{ll}
\textbf{X value} & \textbf{Representing Counts} \\\hline
0 & 0\dots\/4 \\
1 & 5\dots\/9 \\
2 & 10\dots\/14 \\
\dots & \dots\dots\\
19 & 95\dots\/99 \\
20 & 100+ \\
  \end{tabular}

  \medskip
  The file name(s) generated use the text string passed as an argument for
  the prefix, followed by the device identifier in \texttt{major,minor}
  form, with a \texttt{.dat} extension (as an example, with \texttt{-u
  up\_hist} specified on the command line: \texttt{up\_hist\_008,032.dat}.

\subsection{\label{sec:o-V}\texttt{--version}/\texttt{-V}}

  Prints out the \texttt{btt} version, and exits.

\subsection{\label{sec:o-v}\texttt{--verbose}/\texttt{-v}}

  While \texttt{btt} is processing data, it will put out periodic (1-second
  granularity) values describing the progress it is making through the
  input trace stream. The value describes how many traces have been
  processed. At the end of the run, the overall number of traces, trace
  rate (number of thousands of traces per second), and the real time for
  trace processing and output are displayed. Example (note: the interim
  trace counts are put out with carriage returns, hence, they overwrite
  each time):

\begin{verbatim}
# btt -i bp.bin -o btt -v
Sending range data to bttX.dat
Sending stats data to bttX.avg
 287857 t
1414173 t
1691581 t
...
4581291 traces @ 279.7 Ktps
16.379036+0.000005=16.379041
\end{verbatim}

\subsection{\label{sec:o-X}\texttt{--easy-parse-avgs}/\texttt{-X}}

  \emph{Some} of the data produced by default can also be shipped
  simultaneously to another file in an easy to parse form. When
  the \texttt{-o} option is selected (thus producing a file with a
  \texttt{.avg} exentsion), \emph{and} the \texttt{-X} flag is present,
  then \texttt{btt} will generate this file.

  The format is space-delimited values starting with a 3-character
  \emph{record} indicator, then the device information (either major,minor
  or the device name when \texttt{-M} is specified), and then a number of
  fields representing data values. The following table shows the record
  identifiers and the fields provided:

  \bigskip
  \begin{tabular}{|l|l|}\hline
  \textbf{Record} & \textbf{Description}\\\hline
  \texttt{DMI}	& Device Merge Information:\\
		& \#Q \#D Ratio BLKmin BLKavg BLKmax Total\\\hline
  \texttt{QSK}	& Device Q2Q Seek Information:\\
		& NSEEKS MEAN MEDIAN MODE N-MODE mode\ldots\\\hline
  \texttt{DSK}	& Device D2D Seek Information:\\
		& NSEEKS MEAN MEDIAN MODE N-MODE mode\ldots\\\hline
  \texttt{PLG}	& Plug Information:\\
		& \#Plugs \#TimerUnplugs \%TimeQPlugged\\\hline
  \texttt{UPG}	& Unplug Information:\\
		& IOsPerUnplug IOsPerUnplugTimeout\\\hline
  \texttt{ARQ}	& Active Requests at Q Information:\\
  		& AvgReqs@Q\\\hline\hline
  \texttt{Q2Q}  & Queue-to-Queue times:\\
  \texttt{Q2G}  & Queue-to-GetRequest times:\\
  \texttt{S2G}  & Sleep-to-GetRequest times:\\
  \texttt{G2I}  & GetRequest-to-Insert times:\\
  \texttt{Q2M}  & Queue-to-Merge times:\\
  \texttt{I2D}  & Insert-to-Issue times:\\
  \texttt{M2D}  & Merge-to-Issue times:\\
  \texttt{D2C}  & Issue-to-Complete times:\\
  \texttt{Q2C}  & Queue-to-Complete times:\\
                & MIN AVG MAX N\\\hline
  \end{tabular}

  \bigskip
  A sample output file would look like:

  \begin{verbatim}
Q2Q 0.000000001 0.003511356 9.700000000 309906
Q2G 0.000000001 0.774586535 805.300000000 106732
S2G 0.000000001 0.072525952 0.370000000 578
G2I 0.000000001 0.000001125 0.010000000 106732
Q2M 0.000000001 0.730763626 751.820000000 204040
I2D 0.000000001 1.270720538 612.880000000 106948
M2D 0.000000001 0.992355230 428.930000000 203114
D2C 0.000000001 0.008681311 137.020000000 307343
Q2C 0.000000001 1.304370794 805.660000000 308921
DMI 8,16 309907 106729 2.903681286 8 182 1024 19504768
QSK 8,16 309907 167200.935561314 0 0 235708
DSK 8,16 106729 433247.436563633 0 0 33974
PLG 8,16 40824 382 0.008881420
UPG 8,16 1.993361748 1.866492147
ARQ 8,16 12.938165321
  \end{verbatim}

\subsection{\label{sec:o-z}\texttt{--q2d-latencies}/\texttt{-z}}

  This option instructs \texttt{btt} to generate the Q2D latency file
  discussed in section~\ref{sec:lat-q2d}.

\subsection{\label{sec:o-Z}\texttt{--q2d-latencies}/\texttt{-Z}}

  This option generates per-device (and total system) data files. Each
  file contain a data line which resembles a timing graph: low meaning
  I/O inactive, high meaning I/O active. A sample section of two ``active'' regions would be:

\begin{verbatim}
0.000000000 1.0
0.000025733 1.0
0.000025733 1.9
0.000107089 1.9
0.000107089 1.0
0.000107089 1.0
0.005637386 1.0
0.005637386 1.9
0.017323909 1.9
\end{verbatim}

  Which shows an active area from 0.000025733 through
  0.000107089 followed by another at 0.005637386 through
  0.017323909. Figure~\ref{fig:live_plot} shows a sample plot that can
  be generated by such data.

\begin{figure}[b!]
\leavevmode\centering
\epsfig{file=live.eps,width=5.5in}
\caption{\label{fig:live_plot}Sample graph using data from \texttt{-Z}}
\end{figure}

\newpage\section{\label{sec:bno_plot}bno\_plot.py}

Included with the distribution is a simple 3D plotting utility based
upon the block numbers output when \texttt{-B} is specified (see
section~\ref{sec:o-B} for more details about the \texttt{-B option}). The
display will display \emph{each} IO generated, with the time (seconds)
along the X-axis, the block number (start) along the Y-axis and the
number of blocks transferred in the IO represented along the Z-axis.

The script requires Python\footnote{\texttt{www.python.org}} and
gnuplot\footnote{\texttt{www.gnuplot.info}}, and will enter interactive
mode after the image is produced. In this interactive mode one can enter
gnuplot commands at the \texttt{'gnuplot>'} prompt, and/or can change
the viewpoint within the 3D image by \emph{left-click-hold} and moving
the mouse. A sample screen shot can be seen in figure~\ref{fig:bno_plot}.

\subsection*{\texttt{bno\_plot.py} Command Line Options}

\begin{quotation}
\begin{verbatim}

$ bno_plot.py --help

bno_plot.py
	[ -h | --help       ]
	[ -K | --keys-below ]
	[ -v | --verbose    ]
	[ <file...>         ]

Utilizes gnuplot to generate a 3D plot of the block number
output from btt.  If no <files> are specified, it will
utilize all files generated after btt was run with -B
blknos (meaning: all files of the form blknos*[rw].dat).

The -K option forces bno_plot.py to put the keys below the
graph, typically all keys for input files are put in the
upper right corner of the graph. If the number of devices
exceed 10, then bno_plot.py will automatically push the
keys under the graph.

To exit the plotter, enter 'quit' or ^D at the 'gnuplot> '
prompt.
\end{verbatim}
\end{quotation}

\begin{figure}[b!]
\leavevmode\centering
\epsfig{file=bno_plot.eps,width=5.5in}
\caption{\label{fig:bno_plot}Sample \texttt{bno\_plot.py} Screen Shot}
\end{figure}

\clearpage
\newpage\section{\label{sec:appendix}Sample \texttt{btt}
Output}
  Here is a complete output file from a btt run, illustrating a lot of the
  capabilities of btt.
\input{sample-btt-output.tex}

\end{document}
\subsection{\label{sec:o-B}\texttt{--dump-blocknos}/\texttt{-B}}