Can someone explain how to calculate CPU usage?

CPU
1

I’m trying to understand how to calculate CPU usage on my computer. Recently, my system has been running slower than usual, and I suspect that high CPU usage might be the culprit. Could someone guide me on how to measure it accurately and suggest tools or methods to do so? Thanks in advance!

2

Calculating CPU usage can indeed help you diagnose why your system is slowing down. If you’re dealing with Windows, the easiest way to get a quick snapshot of CPU usage is using the Task Manager, but to really understand the numbers, you might want a deeper dive. Here’s a step-by-step guide to both manual inspection and a bit of scripting for continuous monitoring.

Using Task Manager:

  1. Open Task Manager: You can do this by pressing Ctrl + Shift + Esc or right-clicking the taskbar and selecting it.
  2. Go to the Performance Tab: Here, you’ll see a breakdown of your CPU usage over time. The graph will show real-time usage and can help you identify if there’s a pattern to the high usage.
  3. Processes Tab: This tab breaks down CPU usage by process. Sort by the CPU column to see which applications are consuming the most resources.

More Detailed Analysis:

If you want more than just a momentary snapshot, Windows Performance Monitor (PerfMon) can be a powerful tool.

  1. Open Performance Monitor: Typing perfmon in the Start menu search and selecting it.
  2. Add Counters: Click “Performance Monitor” on the sidebar, then click the green + button to add counters. You’ll want to add % Processor Time counter under the processor category.
  3. Monitor Over Time: You can watch this in real-time like Task Manager, but PerfMon lets you set data collector sets to log data over time which is useful for identifying patterns.

Using PowerShell:

For script-based monitoring, PowerShell is pretty handy:

Get-Counter '\Processor(_Total)\% Processor Time'

This command gives an instantaneous value of the total processor usage. If you want to log this data over time, you can set up a loop.

while ($true) {
    Get-Counter '\Processor(_Total)\% Processor Time' | Select-Object -ExpandProperty CounterSamples | Select-Object -Property CookedValue
    Start-Sleep -Seconds 2
}

Linux Users:

For those on Linux, top or htop are your go-tos.

  1. Open Terminal: Type top or htop.
  2. Top Interface: This shows a real-time overview much like Task Manager on Windows. CPU usage is usually displayed as us (user) and sy (system) time.
  3. Detailed Information with htop: If you’ve installed htop, you get a more user-friendly and colorful interface. Use F5 to switch to a tree view that shows process hierarchies clearly.

Alternatively, vmstat (virtual memory statistics) gives you a breakdown of resources over time. A typical usage might look like:

vmstat 2 5

This will log system performance every 2 seconds, for 5 iterations.

Monitoring CPU Over Time:

If you need to continuously monitor over longer periods, setting up logs can be helpful. On Linux, sar (System Activity Reporter) provides historical data.

  1. Install sysstat package: if it’s not already on your system.
    sudo apt-get install sysstat
  2. Enable Data Collection: Edit the sysstat configuration file to ensure data collection is enabled.
  3. Review Historical Data: Use commands like sar -u to review past CPU usage.

General Tips:

  • Number of Cores: Remember that all these percentages can look deceiving if you have a multi-core CPU. 100% usage on a quad-core CPU generally means one core is fully utilized.
  • Background Processes: High CPU usage can sometimes be traced to background processes that you might not need running all the time.
  • Update Drivers/Software: Sometimes high CPU can be fixed by simply updating software or drivers, so keep those current.

By mixing real-time monitoring and historical data collection, you should be able to pinpoint if and when CPU usage spikes, and correlate it with specific applications or times of day.

Good luck! Let us know if you need more detailed instructions on any of these steps.

3

I see @byteguru covered a lot of ground with some solid methods for Windows and Linux. I think they nailed the gist, but there’s some room to throw in a couple more angles.

Windows Alternative: Resource Monitor

Sure, Task Manager is great, but have you checked out Resource Monitor? It gives a bit more granularity.

  1. Open Resource Monitor: You can access it by going to Task Manager > Performance Tab > Open Resource Monitor.
  2. CPU Tab: This will give you a detailed view of CPU usage by service, and unlike Task Manager, it sorts processes by their activity in real-time. Super handy to identify sudden CPU spikes.

Sysinternals Process Explorer

Further on Windows, if you want even more detail:

  1. Download Sysinternals Process Explorer: It’s like Task Manager but on steroids. You can get it from Microsoft’s Sysinternals website.
  2. Inspect CPU Usage: Once downloaded, fire it up and hover over processes. It provides detailed descriptions and highlights processes in red if they’re hogging CPU cycles.

Linux: More Tools and Custom Scripts

I noticed @byteguru didn’t mention nmon which, in my opinion, is a fantastic tool for Linux.

  1. Install nmon: It’s often available in default repositories.

    sudo apt-get install nmon

  2. Run nmon: Type nmon, and press c to view CPU usage. It gives you a beautiful text-based interface that’s quite intuitive.

Alternatively, you can use mpstat for a snapshot at intervals:

mpstat 2 5

This gives a quick rundown like vmstat but focuses on CPU.

Automation with Custom Scripts

For the techies out there who love automation, setting up a CRON job (on Linux) to log CPU usage over time can be a game-changer. Here’s a quick example:

  1. Create a Bash Script to log CPU usage:

    #!/bin/bash
mpstat 1 1 >> ~/cpu_usage_log.txt

  2. Set up a CRON job to run every minute:

    crontab -e

    Add:

    * * * * *  ~/cpu_usage_script.sh

This way, you collect data continuously, and later review patterns.

Cautious Tips

Be wary about over-interpreting results. Sometimes CPU spikes are normal and short-lived. High CPU isn’t always bad if it’s transient or during known heavy tasks.

Consider Alternatives

Also, don’t forget that disk usage or memory issues can manifest as CPU problems. Use tools like RAMMap or DiskUsage on Windows or iotop on Linux to rule out these possibilities.

Final Random Advice

Before diving too deep into command-line tools, make sure to reboot! Yes, it’s basic, but a reboot can clear up temporary glitches that might be causing your woes.

That’s my two cents. Happy hunting! :man_detective:

4

Yeah, @codecrafter and @byteguru gave you quite a bit, but here’s a dose of skepticism for you—starting with the basics: don’t overcomplicate things. Task Manager? Sure, it’s quick and dirty, but it’s hardly the end-all-be-all.

Let’s be real, all these suggestions about fancy tools like PerfMon or expensive third-party apps like Sysinternals Process Explorer are overkill for most people. Also, setting up PowerShell scripts or CRON jobs? Give me a break—most folks don’t have the time or inclination for that.

Now, resource-heavy tools like Resource Monitor and nmon can also contribute to your system slowdown, believe it or not. Logging CPU usage data is all fine and dandy until you realize the logging itself is eating up resources. Irony, right?

But let’s not throw the baby out with the bathwater. To keep things simple, if you’re on Linux, ditch htop and just use top. Press 1 to see all CPU cores individually, and keep an eye on the Load Averages—they often tell a clearer story than CPU usage percentages.

For Windows users tired of Task Manager’s BS, try “Performance Monitor” out for continuous monitoring, if you must. Just remember that it’s way more convoluted than they like to admit.

Also, process explorer has one glaring downside: it’s another resource-taking monster. And don’t even get me started on infection risks associated with some of these tools. Sometimes, old school methods like restarting your system and updating your drivers can really do magic.

So, if your CPU usage is spiking and it’s dragging down your system’s performance, sometimes the simplest solution is a good ol’ fashioned restart or turning off unnecessary startup programs. Not everything requires the whole toolbox. Sometimes a hammer (or a reboot) will do.