Should we enable CPU affinity to improve performance with Windows Server 2012 R2?
In almost all cases, it is unnecessary to use CPU affinity masks in Windows Server 2012 R2 to confine a workload to specific processor threads (supposing each Intel processor core provides two threads). There are several issues to consider.
First, CPU affinity can conflict with the non-uniform memory access (NUMA) architecture used in most modern servers. The whole idea of NUMA is that it is almost impossible for every thread to access the vast amount of available memory at the same speed: Memory closer to a particular core or processor package (socket) can be accessed faster than more distant memory can. So, the server's scheduling routine will attempt to schedule threads on processors that are closest to the memory where the corresponding workload is running. It's almost impossible for a human to know this, so thread affinity will more often drive processing to processors that are in different NUMA zones, actually degrading workload performance.
CPU affinity is often more appropriate for symmetrical multi-processing (SMP) systems where all processors maintain equal access to memory space (different from a NUMA architecture). In an SMP model, any thread can be run on any processor equally, and this is an important prerequisite for parallel processing systems. Still, the operating system can schedule threads automatically based on thread priority. Human intervention will have less impact on performance here, but typically it does not result in better workload performance.
When affinity rules are applied today, it's usually to test the performance of specific processors (or cores within specific processors). IT administrators can see the current thread affinity for a process using the GetProcessAffinityMask function, or use the SetProcessAffinityMask function to specify affinity for the process' threads. As an alternative, IT administrators may elect to use the SetThreadIdealProcessor function to suggest a preferred (ideal) processor for a thread. This function does not force the affinity, and the scheduler can still choose other processors, but setting the ideal processor will prompt the scheduler to use the suggested processor.
Dig Deeper on Enterprise infrastructure management
Related Q&A from Stephen J. Bigelow
Get to know VMware vSphere's Admission Control tool and use it to reserve the resources necessary for VM failover with cluster resource calculations ... Continue Reading
Use heartbeats, VM monitoring and application monitoring to fully examine the causes of VM unresponsiveness. Adjust sensitivity levels to focus on ... Continue Reading
Combine Distributed Resource Scheduler and vSphere High Availability to design balanced failover clusters. Pay attention to affinity rules, which can... Continue Reading
Have a question for an expert?
Please add a title for your question
Get answers from a TechTarget expert on whatever's puzzling you.