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What Is a CPU Bottleneck?

The central processing unit (CPU) is the main processor within a computer system responsible for handling the general calculation and execution of computer program instructions. A CPU’s performance affects the speed of a computer. Whether you have a server running slowly or want to troubleshoot a slow personal computer, a CPU bottleneck could be the culprit. 

What Is a CPU Bottleneck?

A CPU bottleneck occurs when the CPU is the component within a computer system limiting its overall performance. When other components in a computer system can handle workloads better than the CPU and you aren’t seeing the performance you expect, you may have a CPU bottleneck. The CPU could be older than faster components in the computer, or environmental elements such as heat or air flow could be affecting the performance of a CPU.

Is 100% CPU Usage the Same as a Bottleneck?

A bottleneck is not the same as when a CPU reaches full capacity. Busy servers running at CPU maximum capacity might need a CPU upgrade when they handle too much processing. For example, a busy database server might not be able to handle heavy usage if the CPU installed is not made for heavy workloads. An administrator troubleshooting a slow database server might see that the CPU is at 100% capacity, which slows down performance. Slow performance on a server running at full hardware capacity might be the fault of all components (or some components) unable to keep up with data processing.

A CPU bottleneck doesn’t always introduce performance issues. The computer won’t run at peak performance with a slower CPU, but it might be unnoticeable with other fast components installed or when the server handles few concurrent requests. When a computer suffers from a CPU bottleneck, it might still appear to run fast, but it could run faster with additional optimised configurations. For expensive servers hosting corporate applications, purchasing new hardware is expensive, so it’s traditionally more cost-effective to troubleshoot CPU bottlenecks rather than add equipment to speed up a server.

What Causes a CPU Bottleneck?

Certain applications create CPU-intensive tasks. Others can leverage a video card’s graphics processing unit (GPU) to offload tasks from the CPU to the GPU. For example, servers handling machine learning and analytics require extensive CPU resources. A server handling CPU-intensive tasks should handle only these tasks, and applications for other business requests should be installed on separate servers so that several tasks don’t “fight” for CPU resources. Having a strategy for server workloads across an environment will optimise CPU usage and avoid bottlenecks.

All computer equipment should be in a cool room with little humidity. High environmental temperatures affect CPU performance. Servers with little airflow within their cases or installed in a closet where airflow is minimal could suffer from heat-based CPU degradation. 

Ensure that your servers have enough memory and storage. Servers with memory limitations must offload application data to their storage devices. An overloaded server processes application tasks and passes information from the storage device to memory and then back to the CPU. An optimised server loads application information in memory and passes it as needed to the CPU, which passes it back to memory. High memory usage could indicate that the server needs additional random access memory (RAM).

When administrators install applications, sometimes the installation process adds unnecessary processes to start up, meaning these unnecessary processes load when the server reboots. The more processes loading at startup, the more CPU resources are needed to run these applications in the background. Remove these background processes if they’re unnecessary and don’t offer any benefits to server functionality. Also, consider that some hidden applications running in the background could be malware, so scan the server using antivirus and antimalware software.

What Can Happen after a CPU Bottleneck?

Aside from performance degradation, CPU bottlenecks can also cause critical errors on a computer. Critical errors from CPU bottlenecks can cause downtime for applications being hosted on a corporate server. Administrators should monitor servers for errors related to hardware failure.

The biggest observation during CPU bottlenecks is freezes and computer crashes. When the CPU overloads or can’t keep up with tasks, the computer could potentially crash. Chances for crashes and downtime are increased when RAM and storage space are also exhausted during processing. Unless administrators have monitoring software installed on a server, crashes are unexpected or the server reboots without notice.

How to Prevent a CPU Bottleneck

Upgrading hardware might be necessary when servers crash due to CPU bottlenecks. Administrators can easily add hardware resources to cloud-hosted servers in the provider’s administration dashboard, but on-premises administrators must physically install a CPU to a server. On-premises servers must be powered down to install a new CPU, and it must be done carefully to avoid static electricity. Administrators must ground themselves when handling CPUs to avoid destroying the component from static electricity.

A load balancer helps with CPU bottlenecks. Several servers are necessary to balance out workloads when load balancing. The load balancer determines routes for traffic requesting application services instead of sending all traffic to a single server. With several servers behind a load balancer, workloads are spread across each server based on CPU usage and availability.

Administrators responsible for server uptime should always have monitoring software installed across a network environment to detect CPU bottlenecks and high spikes in CPU usage. Both scenarios could indicate that a server is overloaded with requests, or malware could be exhausting resources. Heat-based performance degradation could also be an issue, and server monitoring software notifies administrators of high CPU temperatures.

How to Do a CPU Bottleneck Test

There are several open source bottleneck checkers that can help you determine if your computer needs a CPU upgrade or if hardware must be optimised for better performance. Windows Task Manager monitors CPU usage natively, and Linux has a bundle called sysstat for reviewing CPU activity. Even with native applications, administrators might need better monitoring and statistics to identify a CPU bottleneck.

A few free and open source bottleneck checkers include:


CPU bottlenecks can be frustrating, but optimizing a server is also necessary to keep applications running at peak performance. Monitor your servers for any performance issues to stop critical crashes before bottlenecks cause unforeseen errors on any systems. If CPU bottlenecks persist, consider upgrading server hardware for better performance and stability. 

Looking for a way to upgrade your CPUs without costly disruptions? With FlashStack®, a hybrid cloud infrastructure solution developed jointly by Cisco and Pure Storage, you can address bottlenecks on the fly with the ability to non-disruptively upgrade your compute, network, and storage with zero downtime.

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