Information Technology Reference
In-Depth Information
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4.
Select the Monitor
Performance tab from the contents pane on the right, and then
change the view to Advanced.
5.
Click the Chart Options link.
6.
In the Chart Options dialog box, select CPU from the resource type list. Select the
Custom interval for the time span.
7.
Change the interval to Last 1 Hour(s).
8.
Set the chart type to Line Graph.
9.
Select the VM itself from the list of objects.
10.
From the list of counters, select CPU Usage In MHz (Average) and CPU Ready.
11.
Click OK to apply the chart settings.
CPU Ready
CPU Ready shows how long a VM is waiting to be scheduled on a logical processor. A VM waiting
many thousands of milliseconds to be scheduled on a processor might indicate that the ESXi host
is overloaded, a resource pool has too tight a limit, or the VM has too few CPU shares (or, if no one
is complaining, nothing at all). Be sure to work with the server or application owner to determine
an acceptable amount of CPU Ready for any CPU-intensive VM.
This chart shows CPU utilization for the selected VM, but it won't necessarily help you get to
the bottom of why this particular VM isn't performing as well as expected. In this scenario, we
would fully expect the CPU Usage In MHz (Average) counter to be high; this simply tells you
that the VM is using all the CPU cycles it can get. Unless the CPU Ready counters are also high,
indicating that the VM is waiting on the host to schedule it onto a physical processor, you still
haven't uncovered the cause of the slowness that triggered the help desk ticket. Instead, you'll
need to move to monitoring host CPU usage.
Monitoring a host's overall CPU usage is fairly straightforward. Keep in mind that other
factors usually come into play when looking at spare CPU capacity. Add-ons such as vMotion,
vSphere DRS, and vSphere HA directly impact whether there is enough spare capacity on a
server or a cluster of servers. Compared to previous versions of ESX, the VMkernel will usually
not be as competitive for processor 0 because there are fewer processes to consume CPU time.
VMkernel Stuck on
In older ESX versions, the Service Console was stuck to processor 0 only. It wouldn't get migrated to
other processors even in the face of heavy contention. In ESXi there is no Service Console anymore,
but the VMkernel process is still stuck on processor 0.
