Performance By Design

An event-driven approach to measuring processor execution state. The limitations of the legacy approach to measuring CPU busy in Windows and the need for more precise measurements of CPU utilization are recognized in many quarters across the Windows development organization at Microsoft. The legacy sampling approach is doubtless very efficient, and this measurement facility was deeply embedded in the OS kernel’s Scheduler facility, a chunk of code that is very risky to tamper with. But, for example, more efficient power management, something that is crucial for battery-powered Windows devices, strongly argues for an event-driven alternative. You do not want the OS to wake up from a low power state regularly on an idle machine just to perform its CPU usage accounting duties, for example. A straightforward alternative to periodically sampling the processor execution state is to measure the time spent in each processor state directly. This is accomplished by instrumenting the phase ...

Introduction. This blog entry discusses the legacy technique for measuring processor utilization in Windows that is based on sampling and compares and contrasts to other sampling techniques. It also introduces newer techniques for measuring processor utilization in Windows that are event-driven. The event-driven approaches are distinguished by far greater accuracy. They also entail significantly higher overhead, but measurements indicate this overhead is well within acceptable bounds on today’s high powered server machines. As of this writing, Windows continues to report measurements of processor utilization based on the legacy sampling technique. The more accurate measurements that are driven using an event-driven approach are gaining ground and can be expected to supplant the legacy measurements in the not too distant future. While computer performance junkies like me positively salivate at the prospect of obtaining more reliable and more precise processor busy metri...