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Brunelle % % 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{10 April 2007} \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 0.99.1. 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) or merged (back merge or front merge trace). This is denoted as \emph{Q2I} time. \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} \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 3 phases of an IO: \begin{verbatim} DEV | Q2I I2D D2C ---------- | ------ ------ ------ ( 68, 64) | 0.0% 75.7% 24.2% \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 consecutive IOs. The next session 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. \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. \end{description} \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 ( 65,208) 0.000143901 0.001126610 0.144651899 178548 ( 65,224) 0.000145020 0.001226478 0.124902029 206241 ( 65,240) 0.000144315 0.001199571 0.102415459 129154 ... \end{verbatim} \item[Per Device Averages] The average columns from the above charts, are also presented in their own chart. \end{description} \newpage\section{\label{sec:data-files}Data Files Output} Besides the averages output by default, the following 3 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}. \end{description} Besides the default data files output, there are optional data files which can be generated by btt. These include: \begin{description} \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 Q2C and D2C -- on a per-IO basis can be generated. These are described in sections~\ref{sec:lat-q2c} and~\ref{sec:lat-d2c}. \item[seek details] A data file containing all IO-to-IO sector differences can be output, with details found in section~\ref{sec:seek}. \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: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), here is an example: \begin{verbatim} 20.002179731 8,32 Q 34+8 20.002181199 8,32 I 34+8 20.098329567 8,32 D 34+16 20.002182760 8,32 Q 42+8 20.002183613 8,32 M 42+8 20.098329567 8,32 D 34+16 20.692643206 8,32 C 34+16 \end{verbatim} The columns provide the following information: \begin{enumerate} \item Time of the trace (seconds from the start of the run) \item Device major/minor. \item Trace type \item start block + number of blocks \end{enumerate} For this pair of initial IOs (Q traces at 20.002179731 and 20.002182760), we can follow the insert and merge traces (20.002181199 and 20.002183613 respectively), and the issue (duplicate entries for 20.098329567), and the completion at 20.692643206. Every Q has its corresponding issue trace bounding any insert or merge operations. \newpage\section{\label{sec:lat}\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 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 Q2C or D2C). \newpage\section{\label{sec:seek}Seek Data File} \texttt{btt} can also produce a data file 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 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\section{\label{sec:cmd-line}Command Line} \begin{verbatim} Usage: \texttt{btt} 0.99.1 [ -a | --seek-absolute ] [ -A | --all-data ] [ -B | --dump-blocknos= ] [ -d | --range-delta= ] [ -D | --devices= ] [ -e | --exes= ] [ -h | --help ] [ -i | --input-file= ] [ -I | --iostat= ] [ -l | --d2c-latencies= ] [ -M | --dev-maps= [ -o | --output-file= ] [ -p | --per-io-dump= ] [ -q | --q2c-latencies= ] [ -s | --seeks= ] [ -S | --iostat-interval= ] [ -t | --time-start= ] [ -T | --time-end= ] [ -V | --version ] [ -v | --verbose ] \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-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-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-s}\texttt{--seeks}/\texttt{-s}} This option instruct \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-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} \newpage\section{\label{sec:appendix}Appendix: Sample \texttt{btt} Output} Here is a complete output file from a btt run, illustrating a lot of the capabilities of btt. \begin{verbatim} ==================== All Devices ==================== ALL MIN AVG MAX N --------------- ------------- ------------- ------------- ----------- Q2Q 0.000000001 0.000015439 0.067431982 4485897 Q2I 0.000000277 0.000005085 12.844603081 4485736 I2D 0.000000869 0.000721745 12.845117057 4485736 D2C 0.000151807 0.005254051 0.097569048 4485736 Q2C 0.000156268 0.005980882 12.864868116 4485736 \end{verbatim} \newpage\begin{verbatim} ==================== Device Overhead ==================== DEV | Q2I I2D D2C ---------- | ------ ------ ------ ( 8,160) | 0.0% 1.6% 98.4% ( 8,176) | 0.1% 20.0% 79.9% ( 8,208) | 1.2% 69.2% 29.5% ( 65, 32) | 0.0% 1.1% 98.8% ( 65, 64) | 0.0% 3.6% 96.4% ( 65,176) | 0.0% 2.5% 97.4% ( 65, 96) | 0.0% 15.3% 84.6% ( 8,224) | 0.0% 1.7% 98.3% ( 65,112) | 0.0% 2.4% 97.6% ( 8,240) | 0.0% 2.3% 97.7% ( 65,192) | 0.0% 19.4% 80.6% ( 65,240) | 0.0% 1.3% 98.7% ( 65, 48) | 0.0% 2.3% 97.7% ( 8, 32) | 0.0% 7.0% 93.0% ( 66, 80) | 0.1% 9.9% 90.0% ( 66, 32) | 0.0% 0.7% 99.3% ( 65,224) | 0.0% 18.1% 81.9% ( 65,144) | 0.1% 39.5% 60.5% ( 8,144) | 0.0% 0.7% 99.3% ( 66,144) | 0.0% 1.5% 98.5% ( 66,128) | 0.0% 3.0% 97.0% ( 66,176) | 0.0% 12.5% 87.4% ( 66,224) | 0.0% 10.2% 89.8% ( 66,192) | 0.0% 2.1% 97.9% ( 66,160) | 0.0% 9.4% 90.5% ( 66,240) | 0.0% 9.8% 90.2% ( 66,112) | 0.1% 24.2% 75.7% ( 8, 64) | 0.0% 9.6% 90.4% ( 65,160) | 0.2% 26.2% 73.7% ( 65,208) | 0.0% 2.0% 98.0% ( 66, 16) | 0.0% 4.5% 95.5% ( 65, 0) | 0.0% 2.2% 97.8% ( 65, 16) | 0.0% 1.8% 98.1% ( 66,208) | 0.0% 2.7% 97.3% ( 8,128) | 0.2% 23.7% 76.1% ( 65, 80) | 0.0% 20.0% 80.0% ( 8,112) | 0.0% 1.2% 98.7% ( 65,128) | 0.0% 1.9% 98.1% ( 66, 64) | 0.0% 12.1% 87.9% ( 66, 0) | 0.0% 7.2% 92.8% ( 66, 48) | 0.0% 2.6% 97.4% ( 8,192) | 0.0% 2.3% 97.7% ( 67, 16) | 0.0% 0.8% 99.2% ( 66, 96) | 0.0% 12.3% 87.7% ( 8, 96) | 0.0% 10.3% 89.7% ( 8, 80) | 0.0% 1.7% 98.3% ( 8, 48) | 0.0% 0.7% 99.2% ( 67, 0) | 0.0% 2.6% 97.4% \end{verbatim} \newpage\begin{verbatim} ==================== Device Merge Information ==================== DEV | #Q #D Ratio | BLKmin BLKavg BLKmax Total ---------- | -------- -------- ------- | -------- -------- -------- -------- ( 8,160) | 75145 47890 1.6 | 8 12 1024 601160 ( 8,176) | 91374 55492 1.6 | 8 13 1024 730992 ( 8,208) | 101039 63944 1.6 | 8 12 1024 809256 ( 65, 32) | 67919 44494 1.5 | 8 12 1024 543352 ( 65, 64) | 114614 77396 1.5 | 8 11 1024 916968 ( 65,176) | 93808 62746 1.5 | 8 11 1024 750464 ( 65, 96) | 95537 51705 1.8 | 8 14 1024 764296 ( 8,224) | 95435 49753 1.9 | 8 15 1024 765560 ( 65,112) | 100020 63530 1.6 | 8 12 1024 800160 ( 8,240) | 72282 44700 1.6 | 8 12 1024 578256 ( 65,192) | 95175 59010 1.6 | 8 12 1024 761400 ( 65,240) | 86334 53548 1.6 | 8 12 1024 690984 ( 65, 48) | 69623 44652 1.6 | 8 12 1024 556984 ( 8, 32) | 97816 63116 1.5 | 8 12 1024 782528 ( 66, 80) | 110873 71526 1.6 | 8 12 1024 886984 ( 66, 32) | 79242 53134 1.5 | 8 11 1024 633936 ( 65,224) | 122788 66180 1.9 | 8 14 1024 982304 ( 65,144) | 116636 70205 1.7 | 8 13 1024 933416 ( 8,144) | 72014 49047 1.5 | 8 11 1024 576112 ( 66,144) | 109244 70613 1.5 | 8 12 1024 873952 ( 66,128) | 104688 65381 1.6 | 8 12 1024 837504 ( 66,176) | 79627 47894 1.7 | 8 13 1024 637016 ( 66,224) | 88754 58159 1.5 | 8 12 1024 710032 ( 66,192) | 88919 55417 1.6 | 8 12 1024 711464 ( 66,160) | 102908 71156 1.4 | 8 11 1024 823264 ( 66,240) | 94190 66472 1.4 | 8 11 1024 753520 ( 66,112) | 138799 82027 1.7 | 8 13 1024 1110392 ( 8, 64) | 105011 63892 1.6 | 8 13 1024 840112 ( 65,160) | 93383 55579 1.7 | 8 13 1024 747064 ( 65,208) | 109771 67987 1.6 | 8 12 1024 878168 ( 66, 16) | 96703 56613 1.7 | 8 13 1024 773624 ( 65, 0) | 83752 51532 1.6 | 8 13 1024 670032 ( 65, 16) | 64538 35982 1.8 | 8 14 1024 516320 ( 66,208) | 90636 54306 1.7 | 8 13 1024 725088 ( 8,128) | 96202 59653 1.6 | 8 13 1024 776192 ( 65, 80) | 107945 65672 1.6 | 8 13 1024 863704 ( 8,112) | 78235 52847 1.5 | 8 11 1024 625880 ( 65,128) | 104631 63106 1.7 | 8 13 1024 837048 ( 66, 64) | 86365 50956 1.7 | 8 13 1024 690920 ( 66, 0) | 90413 46722 1.9 | 8 15 1024 723304 ( 66, 48) | 106631 65219 1.6 | 8 13 1024 853048 ( 8,192) | 80591 47154 1.7 | 8 13 1024 644728 ( 67, 16) | 72314 48487 1.5 | 8 11 1024 578512 ( 66, 96) | 90990 54454 1.7 | 8 13 1024 727920 ( 8, 96) | 110805 73522 1.5 | 8 12 1024 886440 ( 8, 80) | 85032 56643 1.5 | 8 12 1024 680400 ( 8, 48) | 87374 57544 1.5 | 8 12 1024 698992 ( 67, 0) | 79611 53515 1.5 | 8 11 1024 636888 ---------- | -------- -------- ------- | -------- -------- -------- -------- DEV | #Q #D Ratio | BLKmin BLKavg BLKmax Total TOTAL | 4485736 2790572 1.6 | 8 12 1024 35896640 \end{verbatim} \newpage\begin{verbatim} ==================== Device Seek Information ==================== DEV | NSEEKS MEAN MEDIAN | MODE ---------- | --------------- --------------- --------------- | --------------- ( 8,160) | 47890 203945.5 0 | 0(2496) ( 8,176) | 55492 252948.8 0 | 0(2360) ( 8,208) | 63944 167845.3 0 | 0(4327) ( 65, 32) | 44494 224708.3 0 | 0(2683) ( 65, 64) | 77396 197838.0 0 | 0(2532) ( 65,176) | 62746 168400.5 0 | 0(2675) ( 65, 96) | 51705 162500.2 0 | 0(2778) ( 8,224) | 49753 206665.7 0 | 0(2753) ( 65,112) | 63530 146289.8 0 | 0(2598) ( 8,240) | 44700 167258.3 0 | 0(2735) ( 65,192) | 59010 217004.7 0 | 0(2724) ( 65,240) | 53548 278194.8 0 | 0(2415) ( 65, 48) | 44652 180710.3 0 | 0(2660) ( 8, 32) | 63116 234049.5 0 | 0(2473) ( 66, 80) | 71526 184981.9 0 | 0(2455) ( 66, 32) | 53134 198369.5 0 | 0(2415) ( 65,224) | 66180 157948.5 0 | 0(2859) ( 65,144) | 70205 195689.7 0 | 0(2734) ( 8,144) | 49047 169282.7 0 | 0(2574) ( 66,144) | 70613 149265.7 0 | 0(2717) ( 66,128) | 65381 165931.1 0 | 0(2687) ( 66,176) | 47894 199744.8 0 | 0(3096) ( 66,224) | 58159 161603.9 0 | 0(2738) ( 66,192) | 55417 153055.3 0 | 0(2828) ( 66,160) | 71156 126479.4 0 | 0(2739) ( 66,240) | 66472 142014.0 0 | 0(2933) ( 66,112) | 82027 115471.3 0 | 0(2961) ( 8, 64) | 63892 136632.0 0 | 0(2655) ( 65,160) | 55579 154668.3 0 | 0(3377) ( 65,208) | 67987 152829.1 0 | 0(2523) ( 66, 16) | 56613 150652.8 0 | 0(2886) ( 65, 0) | 51532 186889.7 0 | 0(2765) ( 65, 16) | 35982 327187.6 0 | 0(2756) ( 66,208) | 54306 243784.1 0 | 0(3076) ( 8,128) | 59653 170797.2 0 | 0(2800) ( 65, 80) | 65672 224501.4 0 | 0(2452) ( 8,112) | 52847 213100.3 0 | 0(2417) ( 65,128) | 63106 207821.8 0 | 0(2686) ( 66, 64) | 50956 198045.0 0 | 0(2896) ( 66, 0) | 46722 205476.3 0 | 0(3159) ( 66, 48) | 65219 142716.6 0 | 0(2869) ( 8,192) | 47154 248778.6 0 | 0(2584) ( 67, 16) | 48487 193335.5 0 | 0(2879) ( 66, 96) | 54454 185100.7 0 | 0(2158) ( 8, 96) | 73522 216187.1 0 | 0(2476) ( 8, 80) | 56643 172561.8 0 | 0(2612) ( 8, 48) | 57544 219104.1 0 | 0(2472) ( 67, 0) | 53515 161613.8 0 | 0(2990) ---------- | --------------- --------------- --------------- | --------------- Overall | NSEEKS MEAN MEDIAN | MODE Average | 2790572 185170.0 0 | 0(131433) \end{verbatim} \newpage\begin{verbatim} ==================== Plug Information ==================== DEV | # Plugs # Timer Us | % Time Q Plugged ---------- | ---------- ---------- | ---------------- ( 8,160) | 45092( 0) | 0.003021834% ( 8,176) | 49430( 0) | 0.003724997% ( 8,208) | 58950( 0) | 0.004506453% ( 65, 32) | 41617( 0) | 0.002710008% ( 65, 64) | 74294( 0) | 0.004971739% ( 65,176) | 59764( 0) | 0.003827258% ( 65, 96) | 47495( 0) | 0.004012641% ( 8,224) | 46806( 0) | 0.003724031% ( 65,112) | 60539( 0) | 0.004272802% ( 8,240) | 41797( 0) | 0.002832794% ( 65,192) | 54754( 0) | 0.004049758% ( 65,240) | 50757( 0) | 0.003466684% ( 65, 48) | 41749( 0) | 0.002783118% ( 8, 32) | 59486( 0) | 0.004102902% ( 66, 80) | 67519( 0) | 0.004698104% ( 66, 32) | 50441( 0) | 0.003229586% ( 65,224) | 60219( 0) | 0.005114778% ( 65,144) | 64699( 0) | 0.005185315% ( 8,144) | 46237( 0) | 0.002824578% ( 66,144) | 67605( 0) | 0.004459997% ( 66,128) | 62418( 0) | 0.004598612% ( 66,176) | 43007( 0) | 0.003277143% ( 66,224) | 54724( 0) | 0.003682546% ( 66,192) | 52395( 0) | 0.003611178% ( 66,160) | 67775( 0) | 0.004347445% ( 66,240) | 62892( 0) | 0.003906526% ( 66,112) | 72351( 0) | 0.005906198% ( 8, 64) | 59642( 0) | 0.004275726% ( 65,160) | 50303( 0) | 0.003841735% ( 65,208) | 64750( 0) | 0.004655374% ( 66, 16) | 53443( 0) | 0.003936557% ( 65, 0) | 48450( 0) | 0.003301599% ( 65, 16) | 33047( 0) | 0.002447028% ( 66,208) | 51060( 0) | 0.003674090% ( 8,128) | 52664( 0) | 0.004009472% ( 65, 80) | 61974( 0) | 0.004623080% ( 8,112) | 50106( 0) | 0.003284028% ( 65,128) | 60047( 0) | 0.004267589% ( 66, 64) | 47590( 0) | 0.003646022% ( 66, 0) | 43413( 0) | 0.003600655% ( 66, 48) | 61984( 0) | 0.004440717% ( 8,192) | 44294( 0) | 0.003120507% ( 67, 16) | 45482( 0) | 0.002852274% ( 66, 96) | 50099( 0) | 0.003970858% ( 8, 96) | 70266( 0) | 0.004743310% ( 8, 80) | 53676( 0) | 0.003530690% ( 8, 48) | 54672( 0) | 0.003527266% ( 67, 0) | 50418( 0) | 0.003217817% ---------- | ---------- ---------- | ---------------- DEV | # Plugs # Timer Us | % Time Q Plugged OVERALL | 54420( 0) | 0.003871155% \end{verbatim} \end{document}