Load averages represent the average number of processes that are either:
- Running (actively using the CPU)
- Waiting to run (e.g., waiting for CPU time)
They give a snapshot of how much work your system has been doing over time. Linux usually reports three numbers for load average, which represent the load over different periods:
- 1 minute
- 5 minutes
- 15 minutes
For example, when you run the uptime or top command, you might see something like this:
load average: 0.5, 0.8, 1.2
This means:
- Over the last 1 minute, on average, there were 0.5 processes running or waiting to run.
- Over the last 5 minutes, on average, there were 0.8 processes running or waiting to run.
- Over the last 15 minutes, on average, there were 1.2 processes running or waiting to run.
2. How Load Average Relates to CPU Cores
Load average numbers should be interpreted in the context of the number of CPU cores available on your system.
- 1 Core CPU: If you have a single-core CPU, a load average of 1.0 means the CPU is fully utilized. A load average of 2.0 means the system is overloaded—there are twice as many processes waiting for CPU time as the system can handle in real-time.
- 4 Core CPU (your case): With a 4-core CPU, a load average of 4.0 means that all cores are fully utilized, and the system is running at full capacity. A load average of 8.0 means the system is overloaded—there are twice as many processes as your CPU can handle efficiently.
Key Points:
- Load average ≤ number of cores: The system is handling the workload well. All processes are getting CPU time without much delay.
- Load average > number of cores: The system is under more load than it can handle efficiently. Some processes are waiting for CPU time, and performance may degrade.
3. How Load Averages Apply to a Virtual Machine
When running a virtual machine (VM), your load average calculations follow the same logic, but with some additional considerations:
- Allocated vCPUs: Virtual machines are allocated a certain number of virtual CPUs (vCPUs). For example, if your VM is assigned 4 vCPUs, this is equivalent to having 4 physical CPU cores in terms of load average calculations.
- Shared Resources: In a virtualized environment, your VM might be sharing physical CPU cores with other VMs. So, even though you have 4 vCPUs allocated, the actual performance might vary depending on the overall load on the host machine (the physical machine running multiple VMs).
4. Example Scenario
Let’s say your VM has 4 vCPUs, and you observe the following load averages:
load average: 2.0, 2.5, 3.0
Here’s how to interpret this:
- 1-minute load (2.0): On average, 2 processes were either running or waiting to run over the last minute. Since you have 4 vCPUs, this means your system is operating at about 50% CPU capacity.
- 5-minute load (2.5): Over the last 5 minutes, the load has been slightly higher, but still within the capacity of your 4 vCPUs.
- 15-minute load (3.0): Over the last 15 minutes, the load has been around 75% of your VM’s capacity. This suggests that your system has been busy but not overloaded.
If you start seeing load averages consistently higher than 4.0 on this VM, it means your CPU resources are becoming a bottleneck, and performance may start to degrade as processes wait for CPU time.
Summary:
- Load average represents the average number of processes either running or waiting for CPU.
- Compare load average values to the number of CPU cores (or vCPUs in a VM) to understand if your system is under or over-utilized.
- For a system with 4 cores, a load average of 4.0 means all cores are fully utilized. Higher than that indicates potential CPU contention.
This understanding will help you monitor your Linux system’s performance and make informed decisions about resource allocation and scaling.
