Shulou(Shulou.com)11/24 Report--

CTOnews.com, December 28, Linux Kernel incorporated restartable sequences (The Restartable Sequences, or RSEQ) several years ago, and GNU C Library has used RSEQ for faster user-space manipulation of each CPU data. RSEQ will be further improved in Linux 6.3, which will be launched next year.

By incrementing each CPU counter, modifying each CPU spin lock, reading / writing to each CPU ring buffer, etc., to avoid atomic operations (atomic operation, operations that are not interrupted by thread scheduling mechanisms), RSEQ can significantly optimize performance to provide excellent benchmark results.

Mathieu Desnoyers, which dominates most of RSEQ's work, has recently been working on extending Restartable Sequences ABI and exposing the NUMA node ID, mm_cid, and mm_numa_cid fields.

CTOnews.com learned that Desnoyers said in the patch introduction:

NUMA node ID allows faster getcpu (2) in libc.

Per-memory-map concurrency id (mm_cid) allows user-space per-cpu data structures to be scaled ideally (down or up).

The concurrent ID allocated in the memory map can be tracked by the scheduler. The scheduler is judged by parameters such as the number of threads running concurrently, CPU affinity (affinity), cpuset applied to these threads, and the number of logical cores.

NUMA-aware concurrency id (mm_numa_cid) is similar to mm_cid, except that it tracks the NUMA node ID associated with each cid.

On NUMA systems, when user space observes that NUMA-aware concurrent ID is associated with a NUMA node, it guarantees that the NUMA node will never be changed unless kernel-level NUMA configuration changes occur. This is useful for running NUMA-aware per-cpu data structures in an environment where processes belonging to cpuset or a set of processes are pinned to a set of kernels belonging to a subset of system NUMA nodes.

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