Steal time is a term used to describe a situation where a virtual machine (VM) in a virtualized environment is waiting for CPU time that is not available. In a virtualized setup, multiple virtual machines run on a single physical host, sharing the host’s resources such as CPU, memory, and storage. The CPU scheduler in the Linux kernel is responsible for allocating CPU time to the different VMs based on their priority and workload.
Steal time occurs when the hypervisor, which is the layer of software that manages the virtual machines, has assigned more virtual CPUs to a VM than the physical CPUs available on the host. In this scenario, the VM may have to wait for CPU time to become available, resulting in a decrease in performance. The time that the VM spends waiting is referred to as steal time.
Steal time is an important metric to monitor in virtualized environments as it directly affects the performance of the VMs. High steal time can indicate that the VMs are over-allocated, and the host may need to be resized or reconfigured to balance the load. On the other hand, low steal time may indicate that the VMs are under-utilized, and the resources can be optimized for better utilization.
To monitor steal time, administrators can use tools like the top command, which displays a real-time summary of the system’s resource usage. In the top output, steal time is displayed as a percentage of total CPU time and can be monitored over time to detect trends. Other tools like htop, glogg, and dstat can also be used to monitor steal time.
Reducing Steal Time for Improved System Performance
To reduce steal time and improve system performance in a Linux environment, administrators can take the following steps:
- Monitor steal time regularly: Use tools such as top, htop, glogg, and dstat to monitor steal time regularly, and detect trends over time. This can help identify when steal time is high and when action is required to reduce it.
- Balance the load: Ensure that the VMs are not over-allocated and that the load is balanced across the host’s physical CPUs. This can be done by resizing the VMs or reconfiguring the hypervisor.
- Use CPU affinity: Assign specific VMs to specific physical CPUs using CPU affinity, which can reduce context switching and improve performance.
- Upgrade hardware: Consider upgrading the host’s hardware if it is underpowered for the workload, as this can reduce steal time and improve performance.
- Use the latest Linux kernel: Ensure that the latest version of the Linux kernel is installed on the host, as this may include performance improvements and bug fixes related to steal time.
- Optimize the workload: Analyze the workload of the VMs and make changes to optimize it, such as reducing the number of processes or scheduling tasks at a different time.
By implementing these steps, administrators can reduce steal time and improve system performance in a Linux environment. It is important to regularly monitor steal time to detect trends and take proactive steps to reduce it.
In conclusion, steal time is an important metric to monitor in virtualized environments, as it can have a significant impact on the performance of the VMs. By understanding the role of steal time in Linux kernel scheduling and monitoring it regularly, administrators can optimize the utilization of resources, improve performance, and ensure that the virtualized environment is running efficiently.