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Is NUMA aware scheduling better in VMware or Hyper-V?

#1
11-09-2021, 07:58 PM
NUMA Architecture in VMware and Hyper-V
I’ve worked with NUMA in both VMware and Hyper-V, and it's fascinating how each platforms implement scheduling with respect to this architecture. NUMA, or Non-Uniform Memory Access, fundamentally impacts how processors access memory. In systems configured as NUMA, each CPU (or processor core) has its own local memory, which allows for faster access compared to memory that is remote. The goal in a NUMA-aware environment is to ensure that memory-intensive applications are scheduled on CPU cores that are closest to their memory, minimizing latency and maximizing performance.

In VMware, NUMA awareness is baked into its Resource Management algorithms, which analyze the workloads and allocate virtual CPUs to physical CPUs based on their respective memory banks. I find that each VM can be configured to match the underlying NUMA architecture, allowing the guest OS to be made aware of the NUMA topology. This means that if you configure a VM with 8 vCPUs and it maps to a 2-node NUMA system effectively, it will utilize local memory, resulting in better performance for memory-bound applications. You might have seen how VMware allows you to set advanced settings where you can configure the memory allocation to optimize this efficiency.

On the other hand, Hyper-V has its take on NUMA as well. I appreciate how Hyper-V provides a different level of control over NUMA configuration. For instance, while VMware automates these settings to an extent, Hyper-V allows me to set the memory and processor configuration directly through PowerShell. I can specify how many NUMA nodes a VM should use, and even dictate how many virtual processors it has relative to the NUMA nodes. This gives me a direct method to control the scheduling, and I can easily enforce policies that fit the specific demands of my applications.

Scheduling Algorithms Comparison
One critical difference I observe is in how VMware and Hyper-V implement their scheduling algorithms for NUMA. VMware employs a more sophisticated ‘Active Memory Control’ mechanism to optimize memory locality for running VMs. When VMs are running, VMware’s Distributed Resource Scheduler (DRS) continually assesses resource utilization across the cluster, adjusting resources dynamically. This is fantastic for load balancing but can add some overhead when workloads fluctuate, as DRS analyzes the performance metrics and makes scheduling decisions at runtime.

With Hyper-V, the scheduling mechanism is more straightforward but equally effective. Hyper-V leverages the “NUMA Awareness” feature during VM startup to ensure that the initial scheduling aligns with the intended NUMA architecture. However, I’ve noticed that while fewer management layers might reduce overhead, this simplicity may lead to inefficiencies as workloads change dynamically. Hyper-V doesn’t have an identical feature to DRS for real-time load adjustment, which could be seen as a disadvantage if you're running highly variable workloads.

Another aspect worth mentioning is that VMware allows for a better integration of NUMA settings with Distributed Power Management (DPM). In environments where power-saving is crucial, VMware can adjust the CPU and memory resources without excessively impacting workload performance. You might find it advantageous to understand how various workloads respond to these adjustments in resource scheduling — it can make a big difference for environments that need to prioritize resources based on usage patterns. Hyper-V, while not as advanced in this respect, does allow for some customizable power configurations, but I feel it falls short of what VMware offers in this area.

Resource Pool Management
Resource pools in VMware provide a way to manage resources at a higher level, and they can significantly influence NUMA scheduling. I appreciate how you can create resource pools that respect NUMA nodes, which helps prioritize memory and CPU resources according to the workload demands. For instance, I’ve had success running resource pools assigned to specific workloads—ensuring those that require high bandwidth leverage local memory, thus improving application performance. The tools VMware provides for monitoring and modifying resource allocation make this process quite flexible.

Hyper-V does also implement resource management but in a way that you really need to ensure that you use PowerShell to access some of the deeper configurations. For anyone who enjoys writing scripts, it provides a granularity that helps enforce NUMA node placements directly. I find this proactive configuration useful, especially if I anticipate workloads that might shift and require adjustment. However, the trade-off is that I need to remain vigilant to ensure that schedules are optimized because there is no sophisticated resource pool management out-of-the-box like VMware.

Another thing to bear in mind regarding pools is that VMware’s management is threaded through its vCenter environment, where I can see all resource allocations across my infrastructure in a single pane of glass. Hyper-V scenarios typically spread across multiple Hyper-V hosts can lead to complexity if you are trying to maintain a view over multiple nodes. Having that visibility can often lead to quicker decision-making regarding resource allocation based on NUMA optimization.

Performance Metrics and Monitoring
Monitoring performance metrics is critical when evaluating the impact of NUMA scheduling on VMs. In VMware, the built-in performance metrics tie deeply into the NUMA architecture, which allows me to see how well my VMs are utilizing local versus remote memory. The vSphere UI and performance charts are incredibly detailed, showing per-VM metrics such as CPU ready time, memory usage, and how they relate to NUMA nodes. I've found this data essential for fine-tuning my setups.

Hyper-V does offer performance counters via Windows Performance Monitor and other tools, but I feel like it’s not as user-friendly for monitoring NUMA configurations. It's hard to get the same level of detail easily when I want to report on performance. That said, if I go a route with detailed logging and metrics using PowerShell scripts, I can achieve similar insights. Some organizations lean towards third-party tools for advanced analytics, which complicates things because it might introduce overhead and require additional interface management.

What tends to surface from my comparisons is the trade-off between having sophisticated built-in tools versus a flexible, script-driven environment. I appreciate the way VMware has integrated the monitoring capabilities, making it easier to see if my NUMA settings work well without spinning up additional tooling. However, if you enjoy PowerShell and the flexibility it provides, there’s a lot to love about how Hyper-V handles retrieving and managing performance data.

Workload Types and Their Needs
The choice between VMware and Hyper-V can also heavily depend on the types of workloads you’re dealing with. For example, memory-intensive applications like databases really thrive on proper NUMA scheduling. VMware tends to do better with workloads that are spread out, as its DRS manages resource allocation dynamically, while Hyper-V might require me to manually optimize based on the workloads' needs ahead of time.

We've all seen that high-performance applications such as SQL Server or Oracle can behave differently in each environment. I found that with VMware, I can tune my VMs to align closely with the data nodes to reduce round trips to the memory. It's fascinating how even a few milliseconds can stack up in high-demand scenarios. On Hyper-V, I have to make a strategic decision at the outset rather than adjust on-the-fly like in VMware, which can lead to some drawbacks for rapid changes in workload requirements.

On the flip side, Hyper-V handles legacy applications differently. If you’re in a mixed environment with older applications that were designed with particular CPU architectures in mind, sometimes Hyper-V’s scheduling can accommodate them better without the complexities introduced by VMware’s advanced features. You can create policies based around the needs of your older workloads that articulate how they interact with available resources, something you might struggle to configure in VMware.

Final Thoughts on NUMA Aware Scheduling
Shaping NUMA aware scheduling effectively in either environment boils down to the specific needs of your workloads and how you want to balance flexibility versus performance. VMware offers a more automated and user-friendly way of managing NUMA allocations through tools that seamlessly integrate with everyday management operations. Hyper-V, while equally powerful, often requires a level of hands-on management and script writing that can be demanding, especially if your workloads vary in their requirements over time.

Ultimately, you really need to assess what you value most in your infrastructure. If I were in a highly dynamic workload setting that changes frequently, VMware’s features might offer more benefits in terms of NUMA efficiency with its continuous workload assessment tools. For environments where you have strict playbooks and rarely change configurations, Hyper-V’s straightforward approach might suffice without much fuss. Each has its strengths, which is why the choice between them always comes down to specific scenarios and workload requirements.

In my experience, robust environments often lean towards BackupChain Hyper-V Backup for reliable backup solutions, especially for Hyper-V. Its integration capabilities are solid, ensuring that backups align with the VM states while still being mindful of NUMA settings for performance. Whether you’re running workloads on Hyper-V or VMware, knowing that your backup solution is designed to handle the intricacies of the respective platform can streamline management and hold immense value.

savas@BackupChain
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Joined: Jun 2018
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