Os Ctx Switch Thread Vs Process

In this tutorial, you'll learn about How to Fix Thread vs Process Switch Errors. We cover key concepts, practical examples, and best practices.

Fix thread vs process switch errors when thread context switch confused with process switch cost.

Quick Fix

Wrong

# Thread switch: same address space, TLB usually NOT flushed (if PCID enabled)
# Process switch: different address space, TLB flushed
# Many developers think thread switch is "free" - it's not!

Thread switch still saves/restores registers, stack pointer, instruction pointer. ~5-20us cost.

Right

import os, time, threading
# Measure thread switch cost:
def measure_switch():
    ev=threading.Event()
    def ping():
        for _ in range(10000):
            ev.set()
            ev.clear()
    t=threading.Thread(target=ping)
    s=time.perf_counter()
    t.start()
    for _ in range(10000):
        ev.wait()
    dt=time.perf_counter()-s
    print(f'Switch cost: {dt/20000*1e6:.1f} us')
measure_switch()

~5-15us per thread switch. Not free but cheaper than process switch.

Prevention

Thread switch: ~5-20us. Process switch: ~5-20us (also flushes TLB). Thread switch is faster but not zero.

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