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Linux Kernel 6.16, LSFMM+BPF, and Power Management and Scheduling in the Linux Kernel (known as "OSPM") Summit
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Web Pro News ☛ Linux Kernel 6.16 Adds X86_NATIVE_CPU Configuration Option
The release of Linux 6.16 is set to impact the x86 ecosystem with notable optimizations and architectural changes designed to maximize performance and hardware support.
Among the most crucial changes is the introduction of the X86_NATIVE_CPU configuration option, which promises to streamline and modernize kernel building for a range of current-generation processors, while dropping support for certain legacy hardware. Phoronix, a respected source for Linux performance and kernel news, describes this move as a “noteworthy change for those building performance-tuned kernels explained” that signals a shift toward targeting only the latest x86 CPUs.
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LWN ☛ A new DMA-mapping API
Leon Romanovsky began his session at the 2025 Linux Storage, Filesystem, Memory Management, and BPF Summit (LSFMM+BPF) by explaining that the improved DMA-mapping API that he has been working on is a group effort. He, Chaitanya Kulkarni, Christoph Hellwig, Jason Gunthorpe, and others are proposing to modernize the API and to "make it more suitable for current kernels". He told the assembled storage and filesystem developers that the progress on the proposal has stalled, but that it was the basis for further work in various areas, so he hoped to find a way to move forward with it.
The existing DMA API is based on struct page, which is fine, but using DMA requires scatter-gather (SG) lists, so there is a lot of conversion between the two formats. In addition, many DMA users have their own formats for the data being transferred, leading to more conversions (between SG and native formats).
A struct scatterlist has two fields that are supposed to contain a CPU address (page_link) and a DMA address (dma_address) but various (ab)uses of the scatterlist have changed the meanings of those fields. For peer-to-peer DMA, page_link is a synthetic CPU address used to get information from the page structure, he said. For dma-buf usage, page_link is null and dma_address is synthetic in order to access the device-private memory. Hellwig pointed out that the dma-buf usage is explicitly invalid according to the documentation, but "the dma-buf people did it anyway and refused to fix it".
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LWN ☛ An update on continuous testing of BPF kernel patches
Ihor Solodrai has been working on the BPF subsystem's continuous-integration (CI) testing for the last six months. At the 2025 Linux Storage, Filesystem, Memory-Management, and BPF Summit, he remotely shared an update on his work, and solicited feedback on how the tests could be further improved. Much of the work he's done has been specific to the BPF subsystem, but some is more generic and could potentially be of use to other subsystems. He also shared some general lessons learned from working on the BPF CI tests.
Before getting to his main update, he first showed a visualizer he has been working on for understanding verifier failures. If one uploads a log file produced by the verifier, the tool shows "something like a debugger view" that lets one step through the verifier's process. Solodrai was optimistic that it could help with debugging, especially for people working on extending the verifier. He said that the tool is currently a prototype, and he would appreciate feedback on it.
The main task Solodrai has been working on since the 2024 Linux Plumbers Conference has been expanding the coverage of the BPF CI tests. In the course of that work, he has fixed a number of other things. Still, his main focus has been on adding GCC to the test suite alongside Clang, and adding testing for sched_ext. At the time of the summit, GCC's BPF implementation was not passing the BPF self-tests, and therefore not included in the CI testing. Since then, that appears to have changed, because recent test runs have included testing for GCC 14.
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LWN ☛ Reports from OSPM 2025, day one
The seventh edition of the Power Management and Scheduling in the Linux Kernel (known as "OSPM") Summit took place on March 18-20, 2025. It was organized by Juri Lelli, Frauke Jäger, Tommaso Cucinotta, and Lorenzo Pieralisi, and was hosted by Linutronix at Alte Fabrik, Uhldingen-Mühlhofen, Germany. The event was sponsored by Linutronix, Arm, and the Scuola Superiore Sant'Anna in Pisa.
The following contains summaries of the sessions; each summary is written by the session presenter. A recording of the entire summit is available as a playlist on the RetisLab YouTube channel. Photos of the event can be found on this Google Photos page or as a 965MB zip archive. The full set of slides from the sessions is also available.