Ichthyostega
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61 lines
3.2 KiB
Text
61 lines
3.2 KiB
Text
Antrag für einen Vortrag auf der FrOSCon 26
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:author: Ichthyostega
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:date: 23.5.2026
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Reading Video data with IO_URING
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.putting a new kernel framework into practical use
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In diesem Vortrag geht es um eine technische Herausforderung, die wir für unser
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OpenSource-Projekt lösen mussten: eine große Menge Video-Daten effizient einlesen.
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Vor diesem Hintergrund möchte ich das neue IO_URING Kernel-Interface erläutern
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und mit vereinfachten Code-Beispielen in C++ zeigen, wie es in eine Applikation
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eingebunden werden kann. Rudimentäre C++ Kenntnisse sollten genügen, um dem
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Vortrag zu folgen, Kennnisse in Systemprogrammierung werden nicht vorrausgesetzt.
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Für die eigentliche Darstellung rechne ich mit 40 Minuten.
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Kurzfassung
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~~~~~~~~~~~
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<b>io_uring</b> is a fairly new I/O interface in the Linux kernel.
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It represents a shift in how applications interact with the kernel.
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Instead of transferring control through a system-call interface into kernel mode,
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operations are submitted asynchronously through shared queues.
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This talk discusses patterns for dealing with asynchronous I/O and demonstrates a setup
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for high-volume file reading using this framework, illustrated with code examples in C++.
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<i>Lumiera</i> is a video editing application under development in C++ and serves here
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as a real-world example showing how asynchronous I/O can play a key role in achieving
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adequate throughput for video processing.
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Langfassung
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~~~~~~~~~~~
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The usual straightforward way to read data from a file is to invoke a <tt>read()</tt>
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function and receive the requested data directly in response. While this function
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is typically exposed through the programming language's standard library, it ultimately
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maps to a system call provided by the OS-kernel. Although this approach is simple in
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terms of program logic, it has the disadvantage that the calling thread is blocked,
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for an unknown amount of time, until the data becomes available.
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Blocking behaviour is particularly problematic in high-performance applications, because it
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reduces control over execution timing and may leave computational resources idle. Various
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interfaces and frameworks have been developed over time to address this issue, both for
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network communication and for file operations. The Linux kernel system call interface
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<b>io_uring</b>, adopted in kernel version 5.1 (2019) and gradually expanded since then,
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takes these efforts one step further by providing a uniform framework for many kinds of
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I/O operations: Client code submits requests to the kernel via shared queue, while
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completed work items are returned asynchronously through a second queue.
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In theory, this model allows extremely high throughput and very low latency.
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In practice, however, structuring client code to achieve these goals remains challenging.
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In our use case -- rendering video frames based on the timeline arrangement made by the
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film editor -- expensive computations must be chained behind I/O operations, all together
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involving a massive amount of data.
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The talk discusses common solution patterns and presents the approach taken by the
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<i>Lumiera</i> project to address these challenges. A simplified demonstration setup
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will then be explained using code examples in C++.
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