![]() However, given the possibility of larger structures for which the performance degradation might be more profound, Andreas was urged to come up with a more elaborate Rust construction that would permit separate access to the 16-bit field, thus avoiding the redundant memory traffic. Apparently, the performance degradation from these duplicate accesses, though measurable, is quite small. ![]() If the 16-bit field indicates that all the fields have been updated by the firmware, it then does a second volatile load of the entire structure and then proceeds to use the values from this second load. #JOURNALY LINUX DRIVER#To the surprise of several Linux-kernel developers in attendance, Andreas's driver instead does a volatile load of the entire structure, 16-bit field and all. One straightforward approach is for the driver to use smp_load_acquire() to access that 16-bit field, and only if the returned value indicates that the other fields have been filled in, access those other fields. This of course requires some sort of memory ordering, both on the part of the device firmware and on the part of the device driver. This structure has a special 16-bit field that is used to report that all of the other fields are now filled in, so that the Linux device driver can now safely access them. As is often the case, there is a shared structure in normal memory in which the device firmware reports the status of an I/O request. I focus on the driver's interaction with device firmware in main memory. I will leave more complete coverage of a great many interesting sessions to others (for example, here, here, and here), who are probably better versed in Rust than am I in any case.ĭevice Communication and Memory OrderingAndreas Hindborg talked about his work on a Rust-language PCI NVMe driver for the Linux kernel x86 architecture. #JOURNALY LINUX SERIES#Instead, I am reporting on what I learned and how it relates to my So You Want to Rust the Linux Kernel? blog series that I started in 2021, and of which this post is a member. #JOURNALY LINUX FULL#I had the honor of attending this workshop, however, this is not a full report. This release also includes a number of updates to RCU, memory ordering, locking, and non-blocking synchronization, as well as additional information on the combined use of synchronization mechanisms. Johann Klähn, SeongJae Park, Xuwei Fu, and Zhouyi Zhou provided many welcome fixes throughout the book. #JOURNALY LINUX CODE#Elad also added support for building code samples on QNX. One of the code samples now use C11 thread-local storage instead of the GCC _thread storage class, courtesy of Elad Lahav. Akira also further improved the new ebook-friendly PDFs, expanded the list of acronyms, updated the build system to allow different perfbook formats to be built concurrently, adjusted for Ghostscript changes, carried out per-Linux-version updates, and did a great deal of formatting and other cleanup. This version boasts an expanded index and API index, and also adds a number of improvements, perhaps most notably boldface for the most pertinent pages for a given index entry, courtesy of Akira Yokosawa. PaulmckThe v2022.09.25a release of Is Parallel Programming Hard, And, If So, What Can You Do About It? is now available! The double-column version is also available from. More recent information may be found in Section 9.5 of Is Parallel Programming Hard, And, If So, What Can You Do About It? The rcu_domain Class Contains lock() and unlock() Member Functions? The most detailed discussion is in the supplementary materials. There are a large number of pitfalls and optimizations, some of which are covered in the 2012 Transactions On Parallel and Distributed Systems paper ( non-paywalled draft). Very roughly speaking, userspace RCU implementations usually have per-thread counters that are updated by readers and sampled by updaters, with the updaters waiting for all of the counters to reach zero. ![]() There are a great many ways to make this work. Therefore, I address these questions in the following sections. ![]() ![]() There was limited time for questions, and each question's answer could easily have consumed the full 50 minutes alloted for the full talk.
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