NICのチューニングと最適化

Welcome to NIC Tuning & Optimization! In this lesson, we'll explore how to fine-tune your Network Interface Card (NIC) for better performance.

A NIC is the hardware that connects your computer to a network. Optimizing its settings can significantly improve network throughput and reduce CPU load.

Before tuning, you need to know your NIC's name. The ip link command lists all network interfaces on your Linux system, showing their status and names.

Common names include eth0, enp0s3, or wlan0 for Wi-Fi.

ethtool is the primary command-line utility for querying and controlling NIC driver and hardware settings on Linux. It's essential for performance tuning.

You can use it to inspect speed, duplex settings, offloading capabilities, and more.

One of ethtool's powerful features is showing what hardware offloading capabilities your NIC supports and which are currently enabled.

This helps you understand if your NIC can handle certain network tasks instead of the CPU.

Offloading means delegating network processing tasks from the main CPU to the NIC's specialized hardware. This frees up CPU cycles for other applications.

• Checksum Offload: NIC calculates/verifies IP, TCP, or UDP checksums.
• Segmentation Offload: NIC handles segmenting large data blocks.

These features are crucial for high-performance networking.

Two important offloading features are TSO and GRO:

• TSO (TCP Segmentation Offload): Allows the operating system to pass a large chunk of data (up to 64KB) to the NIC, which then segments it into smaller TCP packets.
• GRO (Generic Receive Offload): Combines multiple incoming packets into a single larger packet before passing it to the kernel, reducing processing overhead.

Both improve performance for large data transfers.

You can enable or disable specific offload features using ethtool -K. Be cautious when changing these, as incorrect settings can sometimes degrade performance or cause issues.

Always test changes in a controlled environment.

Network Interface Cards use Receive (RX) and Transmit (TX) queues to buffer packets. Multiple queues are especially beneficial on multi-core CPUs, allowing different cores to process different queues.

• More queues can improve parallelism.
• Larger queue sizes can prevent packet drops during bursts.

You can inspect and modify the number of RX/TX queues using ethtool.

• ethtool -g eth0: Shows current and maximum queue settings.
• ethtool -L eth0 rx 4 tx 4: Sets the number of RX and TX queues to 4.

Adjusting these can help distribute network load across CPU cores.

Consider a scenario where your server is experiencing high CPU utilization during heavy network traffic, and you suspect the NIC might not be offloading tasks efficiently.

Which ethtool command would you use to check the current status of offloading features?

Great job! You've learned how to inspect and optimize your Linux Network Interface Card.

• We covered identifying NICs with ip link.
• You met ethtool for checking and configuring NIC settings.
• We explored offloading features like Checksum, TSO, and GRO.
• You also learned about managing RX/TX queues for better parallelism.

These tuning techniques can significantly boost your network's performance. Keep practicing with ethtool!