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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="iotopsect">
<title>Periodically Print I/O Activity</title>
<indexterm>
<primary>script examples</primary>
<secondary>monitoring I/O activity</secondary>
</indexterm>
<indexterm>
<primary>examples of SystemTap scripts</primary>
<secondary>monitoring I/O activity</secondary>
</indexterm>
<indexterm>
<primary>monitoring I/O activity</primary>
<secondary>examples of SystemTap scripts</secondary>
</indexterm>
<indexterm>
<primary>I/O activity, monitoring</primary>
<secondary>examples of SystemTap scripts</secondary>
</indexterm>
<indexterm>
<primary>printing I/O activity (periodically)</primary>
<secondary>examples of SystemTap scripts</secondary>
</indexterm>
<para>This section describes how to monitor I/O activity on the system.</para>
<formalpara id="iotop">
<title>iotop.stp</title>
<para>
<programlisting>
<xi:include parse="text" href="../testsuite/systemtap.examples/io/iotop.stp" xmlns:xi="http://www.w3.org/2001/XInclude" />
</programlisting>
</para>
</formalpara>
<!-- <remark>what does $count do, specifically?</remark> -->
<para><xref linkend="iotop"/> prints out the top ten executables generating I/O traffic every 5-second interval, in descending order. Its output contains the process name and the amount of data read or written by the process, in KB. For example:</para>
<example id="iotopoutput">
<title><xref linkend="iotop"/> Sample Output</title>
<screen>
[...]
Process KB Read KB Written
Xorg 50287 0
staprun 3328 0
multiload-apple 3039 23
sshd 208 1
floaters 14 62
NetworkManager 15 0
gnome-vfs-daemo 8 0
cupsd 3 3
sendmail 4 0
mixer_applet2 3 0
Process KB Read KB Written
Xorg 51886 0
staprun 3328 0
multiload-apple 3039 23
sshd 1344 4
snmpd 90 0
floaters 15 66
NetworkManager 23 0
irqbalance 16 0
pam_timestamp_c 9 0
sendmail 4 0
</screen>
</example>
<para><xref linkend="iotopoutput"/> displays top I/O writes and reads within a random 10-second interval. Note that <xref linkend="iotop"/> also detects I/O resulting from SystemTap activity — <xref linkend="iotopoutput"/> displays reads done by <command>staprun</command>.</para>
<!--
global reads, writes, total_io
probe kernel.function("vfs_read") {
reads[execname()] += $count
}
probe kernel.function("vfs_write") {
writes[execname()] += $count
}
# print top 10 IO processes every 5 seconds
probe timer.s(5) {
foreach (name in writes)
total_io[name] += writes[name]
foreach (name in reads)
total_io[name] += reads[name]
printf ("%16s\t%10s\t%10s\n", "Process", "KB Read", "KB Written")
foreach (name in total_io- limit 10)
printf("%16s\t%10d\t%10d\n", name,
reads[name]/1024, writes[name]/1024)
delete reads
delete writes
delete total_io
print("\n")
}
-->
</section>
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