Os Sched Cpu Affinity

In this tutorial, you'll learn about How to Fix CPU Affinity Errors. We cover key concepts, practical examples, and best practices.

Fix cpu affinity errors when process migrates between CPU cores thrashing L1/L2 caches.

Quick Fix

Wrong

import os
# Default: process can run on any CPU
# OS may migrate between cores, invalidating per-core caches

Cache misses increase. L1/L2 warm data lost on migration. Performance suffers.

Right

import os
# Get number of CPUs:
ncpus=os.cpu_count()
# Set affinity to single CPU:
os.sched_setaffinity(0, {0})  # run only on CPU 0
# Check current affinity:
cpus=os.sched_getaffinity(0)
print(f'Allowed CPUs: {cpus}')
# For thread pools:
from concurrent.futures import ThreadPoolExecutor
# Workers share same affinity as parent process

Process pinned to CPU 0. Cache warm. No migration overhead.

Prevention

Pin CPU-bound threads to specific cores. Reduce cache misses. Use sched_setaffinity.

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