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<h1 id="LTTng_Kernel_Analysis">LTTng Kernel Analysis</h1>
<p>Historically, LTTng was developped to trace the Linux kernel and, over time, a number of kernel-oriented analysis views were developped and organized in a perspective.</p>
<p>This section presents a description of the LTTng Kernel Perspective.</p>
<h2 id="LTTng_Kernel_Perspective">LTTng Kernel Perspective</h2>
<p>The
<b>LTTng Kernel</b> perspective is built upon the
<a href="LTTng.html#Tracing_Perspective">Tracing Perspective</a>, re-organizes them slightly and adds the following views:
</p>
<ul>
<li>
<a href="LTTng-Kernel-Analysis.html#Control_Flow_View">Control Flow View</a> - to visualize processes state transitions
</li>
<li>
<a href="LTTng-Kernel-Analysis.html#Resources_View">Resources View</a> - to visualize system resources state transitions
</li>
</ul>
<p>
<img border="0" src="images/LTTngKernelPerspective.png"/>
</p>
<p>The perspective can be opened from the Eclipse Open Perspective dialog (
<b>Window > Open Perspective... > Other</b>).
</p>
<p>
<img border="0" src="images/OpenLTTngKernelPerspective.png"/>
</p>
<h2 id="Control_Flow_View">Control Flow View</h2>
<p>The
<b>
<i>Control Flow View</i>
</b> is a LTTng-specific view that shows per-process events graphically. To enable it, select
<i>Control Flow</i> under
<i>LTTng</i> within the
<i>Show View</i> window (
<b>Window</b> ->
<b>Show View</b> ->
<b>Other...</b>):
</p>
<p>
<img border="0" src="images/Cfv_show_view.png"/>
</p>
<p>You should get something like this:</p>
<p>
<img border="0" src="images/Cfv_global.png"/>
</p>
<p>The view is divided into the following important sections:
<b><span style="color: #C84545;">process tree</span></b>,
<b><span style="color: #A1C81A;">process TID, PTID and birth time</span></b>,
<b><span style="color: #67A3DC;">states flow</span></b> and the
<b><span style="color: #AD77D7;">toolbar</span></b>.
</p>
<p>The following sections provide detailed information for each part of the Control Flow View.</p>
<h3 id="Process_Tree_and_Information">Process Tree and Information</h3>
<p>Processes are organized as a tree within this view. This way, child and parent processes are easy to identify.</p>
<p>
<img border="0" src="images/Cfv_process_tree.png"/>
</p>
<p>The layout is based on the states computed from the trace events.</p>
<p>A given process may be shown at different places within the tree since the nodes are
<b>unique (TID, birth time) couples</b>. This means that if process B of parent A dies, you'll still see it in the tree. If process A forks process B again, it will be shown as a different node since it won't have the same birth time (and probably not the same TID). This has the advantage that the tree, once loaded, never changes: horizontal scrolling within the
<a href="#anc-cfw-states-flow">states flow</a> remains possible.
</p>
<p>The TID column shows the process node's
<b>thread ID</b> and the PTID column shows its
<b>parent thread ID</b> (nothing is shown if the process has no parent).
</p>
<h3 id="States_Flow">States Flow</h3>
<p>This part of the Control Flow View is probably the most interesting one. Using the mouse, you can navigate through the trace (go left, right) and zoom on a specific region to inspect its details.</p>
<p>The colored bars you see represent
<b>states</b> for the associated process node. When a process state changes in time, so does the color. States colors legend is available through a
<a href="#anc-cfw-toolbar">toolbar button</a>:
</p>
<p>
<img border="0" src="images/Cfv_legend.png"/>
</p>
<p>This dark yellow is what you'll see most of the time since scheduling puts processes on hold while others run.</p>
<p>The vertical blue line is the
<b>current time indicator</b>.
</p>
<h4 id="Using_the_mouse">Using the mouse</h4>
<p>The states flow is usable with the mouse. The following actions are set:</p>
<ul>
<li>
<b>drag horizontally</b>: pan left or right
</li>
<li>
<b>click on a colored bar</b>: the associated process node is selected and the current time indicator is moved where the click happened
</li>
<li>
<b>mouse wheel up/down</b>: zoom in or out
</li>
<li>
<b>drag the time ruler horizontally</b>: zoom in or out
</li>
<li>
<b>drag the time ruler horizontally with the right button</b>:
<a href="LTTng-Kernel-Analysis.html#Zoom_region">zoom region</a>
</li>
<li>
<b>double-click the time ruler</b>: reset zoom
</li>
</ul>
<p>When the current time indicator is changed (when clicking in the states flow), all the other views are
<b>synchronized</b>. For example, the
<a href="LTTng-Kernel-Analysis.html#Events_View_2">Events View</a> will show the event matching the current time indicator. The reverse behaviour is also implemented: selecting an event within the Events View will update the Control Flow View current time indicator.
</p>
<h4 id="Incomplete_regions">Incomplete regions</h4>
<p>You'll notice
<b>small dots</b> over the colored bars at some places:
</p>
<p>
<img border="0" src="images/Cfv_small_dots.png"/>
</p>
<p>Those dots mean the underlying region is
<b>incomplete</b>: there's not enough pixels to view all the events. In other words, you have to zoom in.
</p>
<p>When zooming in, small dots start to disappear:</p>
<p>
<img border="0" src="images/Cfv_zoom.png"/>
</p>
<p>When no dots are left, you are viewing
<b>all the events and states</b> within that region.
</p>
<h4 id="Zoom_region">Zoom region</h4>
<p>To zoom in on a specific region,
<b>right-click and drag the time ruler</b> in order to draw a time range:
</p>
<p>
<img border="0" src="images/Cfv_zoom_region.png"/>
</p>
<p>The states flow horizontal space will only show the selected region.</p>
<h4 id="Tooltips">Tooltips</h4>
<p>Hover the cursor over a colored bar and a
<b>tooltip</b> will pop up:
</p>
<p>
<img border="0" src="images/Cfv_tooltip.png"/>
</p>
<p>The tooltip indicates:</p>
<ul>
<li>the process name</li>
<li>the pointed state name</li>
<li>the pointed state date and start/stop times</li>
<li>the pointed state duration (seconds)</li>
</ul>
<h3 id="Toolbar">Toolbar</h3>
<p>The Control Flow View
<b>toolbar</b>, located at the top right of the view, has shortcut buttons to perform common actions:
</p>
<p>
<img border="0" src="images/Cfv_toolbar.png"/>
</p>
<p>The
<b>Previous event</b> and
<b>Next event</b> buttons update the current time indicator so that it's on the previous or next event.
</p>
<p>The
<b>Previous process</b> and
<b>Next process</b> buttons select the previous and next process node within the process tree.
</p>
<h2 id="Resources_View">Resources View</h2>
<p>This view is specific to kernel trace. To open it, go in
<b>Window</b> ->
<b>Show View</b> ->
<b>Other...</b> and select
<b>LTTng/Resources</b> in the list.
</p>
<p>
<img title=" Example of resources view with all trace points and syscalls enabled" alt=" Example of resources view with all trace points and syscalls enabled" border="0" src="images/Rv_example.png"/>
</p>
<p>This view shows the state of system resources i.e. if changes occured during the trace either on
<b>CPUs</b>,
<b>IRQs</b> or
<b>soft IRQs</b>, it will appear in this view. The left side of the view present a list of resources that are affected by at least one event of the trace. The right side illustrate the state in which each resource is at some point in time.
</p>
<p>Just like other views, according to which trace points and system calls are activated, the content of this view may change from one trace to another.</p>
<p>Each state are represented by one color so it is faster to say what is happening.</p>
<p>
<img title="Color for each state" alt="Color for each state" border="0" src="images/Rv_legend.png"/>
</p>
<p>To go through the state of a resource, you first have to select the resource and the timestamp that interest you. For the latter, you can pick some time before the interesting part of the trace.</p>
<p>
<img title="Shows the state of an IRQ" alt="Shows the state of an IRQ" border="0" src="images/RV_infobox1.png"/>
</p>
<p>Then, by selecting
<b>Next Event</b>, it will show the next state transition and the event that occured at this time.
</p>
<p>
<img title="Shows the next state of the IRQ" alt="Shows the next state of the IRQ" border="0" src="images/RV_infobox2.png"/>
</p>
<p>This view is also synchronized with the others :
<a href="LTTng.html#Histogram_View">histogram</a>,
<a href="LTTng-Kernel-Analysis.html#Events_View_2">events view</a>,
<a href="LTTng-Kernel-Analysis.html#Control_Flow_View">control flow view</a>, etc.
</p>
<h3 id="Navigation">Navigation</h3>
<p>See
<a href="LTTng-Kernel-Analysis.html#Using_the_mouse">using the mouse </a> and
<a href="LTTng-Kernel-Analysis.html#Zoom_region">zoom region </a>.
</p>
<h3 id="Incomplete_regions_2">Incomplete regions</h3>
<p>See
<a href="LTTng-Kernel-Analysis.html#Incomplete_regions">Incomplete regions</a>.
</p>
<h3 id="Toolbar_2">Toolbar</h3>
<p>See
<a href="LTTng-Kernel-Analysis.html#Toolbar">Toolbar</a>.
</p>
<h2 id="Events_View_2">Events View</h2>
<p>The LTTng Kernel Events View
<b>is</b> the plain TMF
<a href="LTTng.html#Events_View">Events Views</a> except that it provide its own specialized viewer to replace the standard one. In short, it has exactly the same behaviour but the layout is slightly different:
</p>
<ul>
<li>
<b>Timestamp</b>: the event timestamp
</li>
<li>
<b>Channel</b>: the event channel (data collector)
</li>
<li>
<b>Event Type</b>: the event type (or kernel marker)
</li>
<li>
<b>Content</b>: the raw event content
</li>
</ul>
<p>
<img border="0" src="images/LTTngKernelEventsViewer.png"/>
</p><hr/>
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