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CS644 week 9:

Advanced I/O

iafisher.com/cs644/spring2025/week9

Problem – I want to do lots of I/O at once

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Problem – I want to do lots of I/O at once

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(not disk I/O)

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Example: Web server with many clients

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Problem – I want to do lots of I/O at once

Example: SSH client

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(reading/writing from terminal and network socket)

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Problem – I want to do lots of I/O at once

Solution: multithreading

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Problem – I want to do lots of I/O at once

Solution: multithreading

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…but that complicates your program

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Problem – I want to do lots of I/O at once

O_NONBLOCK – non-blocking reads/writes

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Problem – I want to do lots of I/O at once

O_NONBLOCK – non-blocking reads/writes

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…but leads to busy polling, wastes CPU

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Problem – I want to do lots of I/O at once

epoll – I/O multiplexing

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Problem – I want to do lots of I/O at once

epoll – I/O multiplexing

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Tell the OS you want to read fd1, fd2, …, then block until one is ready

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Problem – I want to do lots of I/O at once

io_uring – modern I/O multiplexing

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Problem – I want to do lots of I/O at once

io_uring – modern I/O multiplexing

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• Can do ops with fewer (or no!) syscalls

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Problem – I want to do lots of I/O at once

io_uring – modern I/O multiplexing

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• Can do ops with fewer (or no!) syscalls
• OS will do the I/O instead of just notifying

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Problem – I want to do lots of I/O at once

io_uring – modern I/O multiplexing

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• Can do ops with fewer (or no!) syscalls
• OS will do the I/O instead of just notifying
• Operations can be chained

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Problem – I want to do lots of I/O at once

Office hours

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