Network Information Service Overview NIS

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Intricacies of Interrupt Handling in
Linux Anandaraj Thangappan
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Agenda

• Introduction
• Interrupt Handler
• Interrupt Handling
• Bottom Halves

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Introduction

• An interrupt is a communication gateway between
  the device and a processor.
• Interrupt Classification
• Interrupt Latency
• Enabling/Disabling Interrupts

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Interrupt Handler

• It is a function situated in the kernel that
  determines the nature of the interrupt and
  performs whatever actions are needed
• It is invoked whenever an interrupt occurs
• Registering an interrupt handler.
• request_irq()
• free_irq()

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Interrupt Handling

• Top/Bottom Halves
• Why Bottom Halves?
• How to divide works?

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Bottom Halves

• BH
• Task Queues
• Softirqs
• Tasklets
• Work Queues

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BH

• Provides a statically created list of 32 bottom
  halves
• Each BH was globally synchronized
• No two could run at the same time, even on
  different processors

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Task Queues

• Task queues are the kernel's way of deferring
  work until later.
• There are three task queues created and managed
  by the kernel
• A device driver can create and use task queues

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Softirqs

• Softirqs are a set of 32 statically defined bh
  that can run simultaneously on any processor
• Run in interrupt context with all interrupts
  enabled.

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Tasklets

• A tasklet is created dynamically and may run on
  only one CPU at a time
• Two different tasklets can run at the same time
  on two different processors
• Run with all interrupts enabled
• Using Tasklets

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Work Queues

• Workqueue functions run in the context of a
  special kernel process
• Work queue subsystem
• Using Work Queues

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References

• Linux Device Drivers, Jonathan Corbet,
  Alessandro, Rubini, and Greg Kroah-Hartman
• Dynamic Interrupt Request Allocation for Device
  Drivers (www.linuxjournal.com/article/8064)

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• Thank You!
• anandaraj.thangappan_at_wipro.com