numactl

Numactl is a command-line utility and library for controlling NUMA (non-uniform memory access) policies on NUMA-enabled Linux systems. It allows users to run a program with a specified CPU affinity and memory allocation policy, enabling control over where code executes and where memory is allocated. This can improve performance on systems where memory access time depends on the memory node location.

The tool supports several policies and options for binding CPUs and memory to specific NUMA nodes, or for distributing allocations across nodes. Common options include --cpunodebind=nodes to bind CPUs to certain NUMA nodes, --membind=nodes to constrain memory allocations to particular nodes, and --physcpubind=cpus to assign physical CPUs. The --interleave=nodes option interleaves memory allocations across the listed nodes, while --preferred=nodes expresses a preferred set of nodes for allocations. The --localalloc flag requests allocations from the local node first. Commands can be started with these policies, and the current policy or topology can be inspected with --show or --hardware.

In practice, numactl is used to optimize NUMA locality for compute-intensive workloads, databases, and large-scale data processing, by reducing remote memory accesses and improving cache efficiency. It is frequently employed in performance tuning and benchmarking on NUMA architectures. The accompanying libnuma library exposes a programming interface for C programs to query and set NUMA policies, enabling policy control from within applications.

The tool is distributed as part of the numactl package on many Linux distributions and is widely used in environments that require explicit NUMA management.