BTstats

BTstats, which stands for BlockTrace Stats, is intended to extract high level statistics from the traces taken with the Linux kernel blktrace tool. It is implemented in C and its design goal is to be easily extensible and easy to use.

This tool is inspired in btt but its goal is not to be a replacement. btt is very useful as well and you should probably take a look to it. I created BTstats because is easier for me to use and extend. It also fits very well to the way I use blktrace.

BTstats Statistics

In order to understand better this statistics, it is recommended to take a look to blktrace documentation. Currently, BTstats already implements a couple of statistics that I use in my research. The following list explains each of them.

• Number of requests completed by the device.
• Minimun, Average, and Maximun request size.
• Average D2C time per I/O.
• Average D2C time per block. Contrasting to the last bullet, this number shows how well was the behavior of the device per block. This is required since the time per request does not tell the whole story. When the device is servicing a large request, it could take a long time to complete the operation compared to one with small size. However, the first one probably deliver a better performance.
• Average D2C I/O throughput.
• Percentage of sequentiality, defined as 1-(# seeks/total blocks serviced).
• Number of seeks in the device.
• Minimun, Average, and Maximun seek-length.
• Minimun, Average, and Maximun time queue plugged.
• Percentage time queue plugged.
• Merge ratio.
• Q2C and I2C statistics.
• Below you can find an output example and help for more details.

Usage

    Usage: btstats [-h] [-f <file>] [-r <reader>] [-t] [-d <file>] [-i <file>] [<trace> .. <trace>]

    Options:
            -h: Show this help message and exit
            -f: File which list the traces and phases to analyze.
            -t: Print the total stats for all traces.
            -d: File sufix where all the details of D2C will be stored.
                    <timestamp> <Sector #> <Req. Size (blks)> <D2C time (sec)>
            -i: File sufix where all the changes in OIO for I2C are logged.
            -s: File sufix where the histogram of OIO for I2C is printed.
            -r: Trace reader to be used
                    0: default
                    1: reader for driver ata_piix
            <trace>: String of device/range to analyze. Exclusive with -f.

Example

For all the examples, let us assume the files seq1.blktrace.0 and seq2.blktrace.0 exist corresponding to the blktrace files.

• To obtain the stats for the traces:

    # ./btstats seq1
    seq1[0.0000:inf]        =====================================
    Reqs. #: 10739 min: 8 avg: 250.786852 max: 512 (blks)
    Seq.: 100.00%
    Seeks #: 83 min: 8 avg: 56381229.204819 max: 285278432 (blks)
    D2C Total time: 19207.789512 (msec)
    Avg. D2C per I/O: 1.788601 (msec)
    Avg. D2C per block: 0.007132 (msec)
    Avg. D2C Throughput: 68.463842 (MB/sec)
    D2C Max outstanding: 2 (reqs)
    Q2C Total time: 19962.181952 (msec)
    Avg. Q2C per I/O: 1.858849 (msec)
    Avg. Q2C per block: 0.007412 (msec)
    Avg. Q2C Throughput: 65.876519 (MB/sec)
    Q2C Max outstanding: 98 (reqs)
    I2C Max. OIO: 34, Avg: 3.51
    C2D Total: 0
  

• To get stats for ranges of time in the traces, lets say 0-10 and 10-20 seconds:

    # ./btstats seq1@0:10 seq2@10:20
    seq1[0.0000:10.0000]    =====================================
    Reqs. #: 2876 min: 8 avg: 250.556328 max: 256 (blks)
    Seq.: 100.00%
    Seeks #: 4 min: 8 avg: 36798866.000000 max: 147180176 (blks)
    D2C Total time: 5147.943058 (msec)
    Avg. D2C per I/O: 1.789966 (msec)
    Avg. D2C per block: 0.007144 (msec)
    Avg. D2C Throughput: 68.348749 (MB/sec)
    D2C Max outstanding: 2 (reqs)
    Q2C Total time: 4343.682339 (msec)
    Avg. Q2C per I/O: 1.510321 (msec)
    Avg. Q2C per block: 0.006028 (msec)
    Avg. Q2C Throughput: 81.003960 (MB/sec)
    Q2C Max outstanding: 98 (reqs)
    I2C Max. OIO: 34, Avg: 4.08
    C2D Total: 0
    seq2[10.0000:20.0000]   =====================================
    Reqs. #: 5386 min: 8 avg: 251.126625 max: 512 (blks)
    Seq.: 100.00%
    Seeks #: 43 min: 8 avg: 58290205.953488 max: 285278432 (blks)
    D2C Total time: 8873.854489 (msec)
    Avg. D2C per I/O: 1.647578 (msec)
    Avg. D2C per block: 0.006561 (msec)
    Avg. D2C Throughput: 74.424659 (MB/sec)
    D2C Max outstanding: 2 (reqs)
    Q2C Total time: 9270.769963 (msec)
    Avg. Q2C per I/O: 1.721272 (msec)
    Avg. Q2C per block: 0.006854 (msec)
    Avg. Q2C Throughput: 71.238268 (MB/sec)
    Q2C Max outstanding: 70 (reqs)
    I2C Max. OIO: 5, Avg: 2.83
    C2D Total: 0.015813 min: 0.000010 avg: 0.000033 max: 0.000198 (sec)
  

• Another very useful way to obtain statistics is by using the -f option. This file populates the traces and ranges to be used. To start the definition of ranges for one file, the name of the trace should be preceded by the "@" character. Then, the next lines indicate the end of each range of time that will be explored (this assumes that the traces will be explored from time 0). To get stats from traces trace1 in ranges 0-100 and 100-200 and trace2 with ranges 0-200 and 200-400, the file used will be:

    @trace1
    100
    200
  
    @trace2
    200
    400
  

Requirements

This version of btstats strongly use glib and gsl libraries. Make sure to have this before trying to compile (Ubuntu: libglib2.0-dev and libgsl-dev).

Plugin Development

I have not had the time to do a guide for the development of a btstats plugin. I would suggest to start by looking at some simple plugin as is the case of reqsize.

License

BTstats is distributed under the ISC license. You can find details in the LICENSE file.