An Overview of Processor Bottlenecks

An Overview of Processor Bottlenecks

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Troubleshooting High CPU utilization can be addressed from a couple of different standpoints.  In the first instance, you might have a single process consuming CPU - essentially a runaway process.  However, what happens if there is no runaway process, and yet the CPU utilization still continues to run high, sometimes at 100% for an extended period of time?  You may be experiencing a processor bottleneck instead.  Processor bottlenecks occur when the processor is so busy that it cannot respond to requests for a significant period of time.

The major indicators of a processor bottleneck are identifiable using Performance Monitor.  There are two main counters to be aware of:

Counter Name Indicator Values to Consider
Processor (_Total) \ % Processor Time Processor Utilization Sustained values > 90% on a single processor machine, or > 80% on a multiprocessor machine should be investigated
System \ Processor Queue Length Current Depth of the thread Scheduler Ready Queue If the Ready threads per processor value is > 2 with some frequency this may indicate a processor bottleneck.

Interpretation of these two counters should be performed with the following considerations:

  • Processor state is sampled hundreds of times per second.  These results are accumulated over the interval for which the data is gathered.  Thus, if the interval used for data gathering is a small one, you may have skewed data
  • Applications capable of absorbing any free processor cycles (for example screen savers or web page animation controls) should be excluded from the analysis as they can cause skewed data
  • Processor Queue Length is a counter that reflects a point in time data point based on the last sample of the processor state
  • Most threads are in a voluntary Wait state for much of the time.  The remaining threads actively trying to run (a subset of the total number of existing threads) form the upper limit on the number of threads you can see in the processor queue

A combination of high processor utilization and a lengthy processor queue may be an indication that the processor is overloaded.  Remember however, that a misbehaving application can cause the same symptoms.  For example, if an application thread is caught in an infinite loop, that can drive processor utilization to 100% (although you would most likely catch this in Task Manager).   Additionally, remember that sudden spikes may create a scenario where it appears that you have a processor bottleneck.  Having a performance baseline of the server is key to understanding and detecting abnormal conditions and take corrective actions in a timely fashion.  Remember that any normal workload that drives the CPU to 100% utilization on a consistent basis for an extended period of time should be investigated.  Even if the queue of Ready threads is low, there is obviously some pressure on the CPU.  A faster processor would provide relief.  If the workload is multi-threaded, moving from uniprocessor to multiprocessor may offer additional relief.  Dividing the workload among a cluster of machines may be another option.  Lastly, consider this scenario: If the workload is something that can be shifted to a different time when there is less work being done on the machine, that may help to ease the pressure on the CPU - a common example would be running backups during business hours.  These operations can cause severe I/O and Network pressure as well as CPU utilization - moving them to the evenings / weekends helps to reduce the load during business hours.

That brings us to the end of this post.  In our next post, we'll cover the different ways in which a processor executes instructions.  Until next time ...

Additional Resources:

- CC Hameed

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  • nice post, looking forward to next one

  • As a New Year's Resolution I'm planning to blog at least once a week. Hopefully I will maintain this

  • What does it mean when consistently high PQL's coincide with consistently low CPU utilizations?

    My instinct would be to suggest "poorly written code" as an answer, but I'd like some info to either back up that info or refute it.




  • Hey Thanks and nice post... Having one issue, my server shows avg 10 to 20 queue thread and cpu utilization 45% to 60%. doubt, since cpu is free for at least 40% then why the queue is increasing?

  • I read several places that only 1 antivirus program should be running/installed on a computer at one time, but some would work also. Well this self proclaimed computer guru that started working here has put about 4 programs on this Acer. It already has a slow connection but now it is impossible. We cant get into our business files at times. We have to connect to a certain server for that. My question is about this combo of programs going on here,. Are they compatible or are they causing this very very slow performance. Spybot-S&D Start Center, IObit Malware, Advanced SystemCare6 & Smart Defrag. Should some of these be deleted?? Please help!

  • @CharcharC:  I would say so.  A captured Perfmon log should be able to point to a particular resource/process that is chewing up resources on the machine.  You can also try using MSCONFIG and see if that helps.  If it does, then by a process of elimination might point to the culprit.  There's really no reason to run of those other apps IMO.

    Good luck!