Tips for Using Performance Monitor CPU Counters

Sometimes, a performance monitor counter measures potential bottlenecks you may not think about. For example, there is a Performance Monitor counter called System: % Total Privileged Time. What this counter measures is what percent of the System: % Total Processor Time counter is used for running Kernel Mode (sometimes also referred to as privileged mode) code. As you may know, a CPU running under Windows Server can run in two modes: kernel or user mode. Most, but not all, of the operating system code is run in kernel mode, and some operating system and all user applications are run in user mode.

So what does all this mean? If you notice that the System: % Total Privileged Time counter is running at greater than 20%, this is an indication that your server’s I/O may be bottlenecked. Why? Because the I/O driver runs in kernel mode, and one indication of high I/O use is indicated by a higher percentage of Privileged Time use. If this number is high, and the % Disk Time counter is over 55%, you can be fairly sure that I/O is a bottle neck in your server.

Besides intensive I/O use, a high value for this counter can indicate potential network driver, disk driver, or hardware problems. If you are getting a 25% or higher reading for the % Total Privileged Time counter, but the % Disk Time counter is less than 55%, then most likely it is not an I/O bottleneck, but a driver or hardware problem, and you should starting taking a look at these.

While this is not a counter I watch regularly, you might consider using it to help confirm your suspicions of a potential I/O bottleneck on your server.

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