Os Ctx Switch Soft Vs Hard

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

Fix soft vs hard irq errors when long-running interrupt handler (hard IRQ) disables all interrupts.

Quick Fix

Wrong

import os, time
# In kernel: interrupt handler that runs too long
# Disables all interrupts on that core during execution
# Simulated: holding spin_lock_irqsave for long time

Hard IRQ runs with interrupts disabled. Too long = missed interrupts, timer jitter, system unresponsive.

Right

# Linux splits interrupt handling:
# 1. Hard IRQ: minimal, quick (ack, schedule softirq)
# 2. SoftIRQ/SoftIRQ daemon: heavy work, interrupts enabled
import os
# Check interrupt stats:
with open('/proc/interrupts') as f:
    headers=f.readline()
    for line in f:
        if 'timer' in line:
            print(f'Timer IRQ: {line.strip()}')
# Check softirq stats:
with open('/proc/softirqs') as f:
    for line in f:
        if 'TIMER' in line:
            print(f'SoftIRQ: {line.strip()}')

Hard IRQ minimal. Heavy work deferred to SoftIRQ (ksoftirqd).

Prevention

Keep hard IRQ handlers minimal. Use threaded IRQs or SoftIRQ for heavy work.

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