Polling

Definition

Polling is a technique used in computer architecture to check the status of an I/O device at regular intervals to see if it needs attention or has completed a task. This method helps manage communication between the CPU and peripheral devices, ensuring that data transfers are timely and efficient, although it can lead to wasted CPU cycles when devices are idle.

5 Must Know Facts For Your Next Test

1. Polling can lead to inefficient CPU usage, especially if devices are not frequently needing attention, as the CPU may waste cycles checking their status.
2. In systems with many I/O devices, polling can become particularly cumbersome, as it may require multiple checks per second for each device.
3. Polling is simpler to implement than interrupts since it does not require complex mechanisms for signaling the CPU when an event occurs.
4. Some systems use a hybrid approach, combining polling and interrupts to balance responsiveness with efficiency.
5. The frequency of polling intervals can significantly affect system performance; shorter intervals increase responsiveness but can lead to higher CPU overhead.

Review Questions

• How does polling compare to interrupt-driven I/O in terms of efficiency and CPU usage?
  • Polling and interrupt-driven I/O serve different purposes in managing device communication. Polling involves regularly checking the status of an I/O device, which can lead to inefficient CPU usage as it may waste cycles when devices are idle. In contrast, interrupt-driven I/O allows devices to signal the CPU only when they need attention, leading to more efficient use of processing power. While polling is straightforward to implement, it may not be ideal for systems with high device interaction or multiple peripherals.
• Discuss the advantages and disadvantages of using polling in I/O operations within a computer system.
  • Polling has its advantages, including simplicity in implementation and predictable timing for checking device statuses. However, its disadvantages include potential inefficiency due to wasted CPU cycles when devices are idle, and increased overhead when managing multiple devices. In systems with low I/O activity, polling can work well, but in high-demand environments, using interrupts or direct memory access may provide better performance and responsiveness.
• Evaluate how the choice between polling and other I/O management techniques like DMA impacts overall system performance.
  • The choice between polling and techniques like DMA significantly influences system performance based on workload characteristics. Polling can lead to increased CPU load and latency in data processing if devices remain idle frequently. In contrast, DMA allows devices to transfer data directly to memory without CPU involvement, freeing up processing resources for other tasks. Thus, implementing DMA in scenarios with high data throughput demands reduces latency and increases overall efficiency, demonstrating how strategic choices in I/O management can enhance system performance.

Related terms

Interrupt: A signal sent to the CPU that temporarily halts the current execution process, allowing the system to respond to an event or condition requiring immediate attention.

DMA (Direct Memory Access):

A system that allows certain hardware subsystems to access main system memory independently of the CPU, reducing the need for polling.

Device Driver: A specialized program that allows the operating system to communicate with hardware devices, managing their functions and enabling efficient polling or interrupt handling.