It’s perfcounter week on the NDIS blog!


Actually every week is perfcounter week.

Performance counters are an essential tool for devs, ops, … and marketing. Yet they’re often not well understood. Fortunately, under the hood, performance counters are very simple: a perfcounter is just a number that counts things.

Before we get too far along, let’s agree on a bit of terminology:

A counter is a single measurement, like the number of interrupts per second.
A counter set is a group of related counters, like a group of 9 counters relating to TCP/IP. The CLR calls this a category name, and some Win32 APIs call this a performance object. They all refer to the same thing. I’ll stick with the counter set term on this blog.
A counter instance is a specific thing that can be measured, like a network adapter.

Conventionally, you can specify a counter using the counter path notation. The formal grammar is documented here, but most commonly in Networking, you’ll use the subset that looks like this:

Counter Set(Counter Instance)\Counter

So for example, Network Interface(BitBlaster 2000)\Bytes Sent/sec belongs to the Network Interface counter set, targets the BitBlaster 2000 instance, and measures the Bytes Sent/sec counter.

Counters in a GUI

Enough terminology; let’s do things. If you’ve used perfcounters before, you’ve probably come across Performance Monitor, aka perfmon.  You can use this built-in tool to rummage around and visualize the various perfcounters. It’s great if you don’t quite know which counter you’re looking for, or if you need a quick overview of what some counter is doing. Here’s how I use it:

  1. Launch perfmon.exe.
  2. In the tree on the left, select Performance Monitor to get to the graph.
  3. In the graph’s toolbar, click the Delete button (it looks like a red X) to remove any pre-added counters. We’ll add our own.
  4. Then click the Add button (it looks like a green +) to add more interesting counters.
  5. In the dialog that appears, the upper-left quadrant shows all counter sets. If you expand one of the dropdowns inside a counter set, you can see an individual counter. Once you select an individual counter, you can see all applicable counter instances in the lower-left quadrant.
  6. Select a counter instance, then click the Add button to add the counter to the list of counters to monitor.
  7. Once you’ve added all the counters you like, click OK.

That will look like this:

The Add Counters dialog lets you drill down into counter sets, counters, and instances.  Once you select an instance you like, click the Add button to add it to the list of counters to monitor.

To make the graph look right, you may have to fiddle with the scale a bit. Right-click on the counter at the bottom of the main window, select Properties, and change the Scale dropdown on its properties page.

Counters in PowerShell

Perfmon is great for high-level explorations, but you’ll eventually run up against its limitations. For example, it won’t send you an email if a counter goes out of tolerance. For the most flexibility, we need to go beyond a GUI.

Performance counters have been around for a while, so there are plenty of APIs, libraries, and tools you can choose from. I will use PowerShell for illustration, but you can use whatever API you prefer. Generally the concepts exposed in PowerShell will map onto any API.

Let’s poll a counter from PowerShell:

PS C:\> Get-Counter '\Processor(0)\% DPC Time'
Timestamp CounterSamples
--------- --------------
6/4/2017 10:14:10 \\jtippet-d\processor(0)\% dpc time :
1.56111154738975

The counter values come back as real numbers, so you can perform all the usual arithmetic on them. For example, you can check if the counter value exceeds 10%:

Get-Counter '\Processor(0)\% DPC Time' -Continuous | % {
$percentDpcTime = $_.CounterSamples[0].CookedValue
if ($percentDpcTime -gt 10) {
Send-MailMessage -To 'me@example.com' -Subject 'Alert' -BodyAsHtml "% time at DPC: $percentDpctime"
} }

(Don’t actually build a production monitoring system like this – there’s off-the-shelf software that has way more features.)

Now that we have some of the basics down, next time we’ll take a look at the goodies you can use to measure the heartbeat of the Windows network stack.

Comments (2)

  1. virteract says:

    How can perfcounter be used in marketing?

    1. One feature request we had: show me exactly how many cycles my LWF uses, and also how many cycles my *competitor's* LWF uses... so we can brag about our perf. I declined the feature, on the basis that I don't want to get involved in marketing claims.

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