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<?xml version='1.0'?>
<!DOCTYPE section PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
]>
<section id="traceiosect">
<title>Track Cumulative IO</title>
<indexterm>
<primary>script examples</primary>
<secondary>tracking cumulative I/O</secondary>
</indexterm>
<indexterm>
<primary>examples of SystemTap scripts</primary>
<secondary>tracking cumulative I/O</secondary>
</indexterm>
<indexterm>
<primary>tracking cumulative I/O</primary>
<secondary>examples of SystemTap scripts</secondary>
</indexterm>
<indexterm>
<primary>cumulative I/O, tracking</primary>
<secondary>examples of SystemTap scripts</secondary>
</indexterm>
<indexterm>
<primary>monitoring cumulative I/O</primary>
<secondary>examples of SystemTap scripts</secondary>
</indexterm>
<indexterm>
<primary>printing I/O activity (cumulative)</primary>
<secondary>examples of SystemTap scripts</secondary>
</indexterm>
<para>
This section describes how to track the cumulative amount of I/O to the system.
</para>
<formalpara id="traceio">
<title>traceio.stp</title>
<para>
<programlisting>
<xi:include parse="text" href="../testsuite/systemtap.examples/io/traceio.stp" xmlns:xi="http://www.w3.org/2001/XInclude" />
</programlisting>
</para>
</formalpara>
<!--
<remark>what do $return, $length, and $count return, specifically? when i substituted $return for $length here, script still ran but gave me bigger numbers. errored out with $length. where documented?</remark>-->
<para>
<xref linkend="traceio"/> prints the top ten executables generating I/O traffic over time. In
addition, it also tracks the cumulative amount of I/O reads and writes done by those ten
executables. This information is tracked and printed out in 1-second intervals, and in
descending order.
</para>
<!-- next 3 indexterms for $return -->
<indexterm>
<primary>local variables</primary>
<secondary>sample usage</secondary>
<tertiary>$return</tertiary>
</indexterm>
<indexterm>
<primary>variables (local)</primary>
<secondary>sample usage</secondary>
<tertiary>$return</tertiary>
</indexterm>
<indexterm>
<primary>$return</primary>
<secondary>sample usage</secondary>
<tertiary>local variables</tertiary>
</indexterm>
<para>
Note that <xref linkend="traceio"/> also uses the local variable <command>$return</command>,
which is also used by <xref linkend="scriptdisktop"/> from <xref linkend="disktop"/>.
</para>
<!--<para><xref linkend="traceio"/> is similar to <xref linkend="iotop"/> (from <xref linkend="iotopsect"/>); both SystemTap scripts print out the top ten executables generating I/O traffic over time. However, <xref linkend="traceio"/> tracks the <emphasis>cumulative</emphasis> amount of I/O reads and writes done by the system's top ten executables. This information is tracked and printed out in 1-second intervals and in descending order.</para>-->
<example id="traceiooutput">
<title><xref linkend="traceio"/> Sample Output</title>
<screen>
[...]
Xorg r: 583401 KiB w: 0 KiB
floaters r: 96 KiB w: 7130 KiB
multiload-apple r: 538 KiB w: 537 KiB
sshd r: 71 KiB w: 72 KiB
pam_timestamp_c r: 138 KiB w: 0 KiB
staprun r: 51 KiB w: 51 KiB
snmpd r: 46 KiB w: 0 KiB
pcscd r: 28 KiB w: 0 KiB
irqbalance r: 27 KiB w: 4 KiB
cupsd r: 4 KiB w: 18 KiB
Xorg r: 588140 KiB w: 0 KiB
floaters r: 97 KiB w: 7143 KiB
multiload-apple r: 543 KiB w: 542 KiB
sshd r: 72 KiB w: 72 KiB
pam_timestamp_c r: 138 KiB w: 0 KiB
staprun r: 51 KiB w: 51 KiB
snmpd r: 46 KiB w: 0 KiB
pcscd r: 28 KiB w: 0 KiB
irqbalance r: 27 KiB w: 4 KiB
cupsd r: 4 KiB w: 18 KiB
</screen>
</example>
<!--
global reads, writes, total_io
probe kernel.function("vfs_read").return {
reads[execname()] += $return
}
probe kernel.function("vfs_write").return {
writes[execname()] += $return
}
probe timer.s(1) {
foreach (p in reads)
total_io[p] += reads[p]
foreach (p in writes)
total_io[p] += writes[p]
foreach(p in total_io- limit 10)
printf("%15s r: %8d KiB w: %8d KiB\n",
p, reads[p]/1024,
writes[p]/1024)
printf("\n")
# Note we don't zero out reads, writes and total_io,
# so the values are cumulative since the script started.
}-->
</section>
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