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LWN on Kernel and Recent Linux Talks
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READ_ONCE(), WRITE_ONCE(), but not for Rust
The READ_ONCE() and WRITE_ONCE() macros are heavily used within the kernel; there are nearly 8,000 call sites for READ_ONCE(). They are key to the implementation of many lockless algorithms and can be necessary for some types of device-memory access. So one might think that, as the amount of Rust code in the kernel increases, there would be a place for Rust versions of these macros as well. The truth of the matter, though, is that the Rust community seems to want to take a different approach to concurrent data access.
An understanding of READ_ONCE() and WRITE_ONCE() is important for kernel developers who will be dealing with any sort of concurrent access to data. So, naturally, they are almost entirely absent from the kernel's documentation.
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A high-level quality-of-service interface
Quality-of-service (QoS) mechanisms attempt to prioritize some processes (or network traffic, disk I/O, etc.) over others in order to meet a system's performance goals. This is a difficult topic to handle in the world of Linux, where workloads, hardware, and user expectations vary wildly. Qais Yousef spoke at the 2025 Linux Plumbers Conference, alongside his collaborators John Stultz, Steven Rostedt, and Vincent Guittot, about their plans for introducing a high-level QoS API for Linux in a way that leaves end users in control of its configuration. The talk focused specifically on a QoS mechanism for the scheduler, to prioritize access to CPU resources differently for different kinds of processes. (slides; video)
Historically, the server market has been a big factor in optimizing the performance of the Linux scheduler, Yousef said. That has changed somewhat over time, but at least initially the scheduler was extremely throughput-focused. In recent years, there has been more concern given to interactivity, but there are still a lot of stale assumptions about how to wring the best performance out of a Linux system. POSIX hasn't evolved to cover new developments, applications still often spawn one thread per CPU core as though the system has no other workloads running, and so on.
The current default scheduler in the kernel, EEVDF, has a number of configurable parameters that can be adjusted for the system as a whole or per-process; Yousef thought that the best way to implement a QoS API for Linux was to give the scheduler enough information about processes to set reasonable default values for the existing configuration options. In the past, people have focused on the kernel interface used to communicate with the scheduler, he said, but that isn't the problem that matters. What matters is providing a high-level API for applications that doesn't require detailed knowledge of the scheduler's configuration to use.
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Format-specific compression with OpenZL
Lossless data compression is an important tool for reducing the storage requirements of the world's ever-growing data sets. Yann Collet developed the LZ4 algorithm and designed the Zstandard (or Zstd) algorithm; he came to the 2025 Open Source Summit Japan in Tokyo to talk about where data compression goes from here. It turns out that we have reached a point where general-purpose algorithms are only going to provide limited improvement; for significant increases in compression, while keeping computation costs within reason for data-center use, turning to format-specific techniques will be needed.