Alyssa Rosenzweig provides an update on the Panfrost driver for Mali GPUs on the Collabora blog. “In the past 3 months since we began work on Bifrost, fellow Collaboran Tomeu Vizoso and I have progressed from stubbing out the new compiler and command stream in March to running real programs by May. Driven by a reverse-engineering effort in tandem with the free software community, we are confident that against proprietary blobs and downstream hacks, open-source software will prevail.”
Just over 7,500 non-merge changesets have been pulled into the mainline repository since the opening of the 5.8 merge window — not a small amount of work for just four days. The early pulls are dominated by the networking and graphics trees, but there is a lot of other material in there as well. Read on for a summary of what entered the kernel in the first part of this development cycle.
Recently, the DMA-BUF heaps interface was added to the 5.6 kernel. This interface is similar to ION, which has been used for years by Android vendors. However, in trying to move vendors to use DMA-BUF heaps, we have begun to see how the DMA API model doesn’t fit well for modern mobile devices. Additionally, the lack of clear guidance in how to handle cache operations efficiently, results in vendors using custom device-specific optimizations that aren’t generic enough for an upstream solution. This article will describe the nature of the problem; the upcoming second installment will look at the path toward a solution.
The FreeNAS distribution implements network-attached storage on top of the ZFS filesystem; it was reviewed here back in 2015. FreeNAS has always been based on FreeBSD, but now iXsystems, the company behind this system, has announced a new version, called TrueNAS SCALE, that will be based on Debian. “Linux is a key requirement to achieve some of the SCALE project goals“. More information about those goals will evidently be forthcoming in the future.
The 5.7 kernel was released on May 31. By all appearances this was a normal development cycle, unaffected by the troubles in the wider world. Still, there are things to be learned by looking at where the code came from this time around. Read on for LWN’s traditional look at who contributed to 5.7, who supported that work, and the paths by which it got into the mainline.
The FSGSBASE patch series is up to its thirteenth version as of late May. It enables some “new” instructions for the x86 architecture, opening the way for a number of significant performance improvements. One might think that such a patch series would be a shoe-in, but FSGSBASE has had a troubled history; meanwhile, the delays in getting it merged may have led to a number of users installing root holes on their Linux systems in the hope of improving security.
Linus has released the 5.7 kernel right on schedule. Headline features in 5.7 include x86 split-lock detection, thermal-pressure management, frequency invariance in the load-tracking code, coexistence between BPF and realtime preemption, support for BPF security hook programs (formerly called the KRSI security module), a new, Microsoft-blessed exFAT filesystem implementation, and more. The final patch to be merged was this one deprecating the long-standing 80-column limit for kernel source.
The Linux deadline scheduler supports realtime systems where applications need to be sure of getting their work done within a specific period of time. It allocates CPU time to deadline tasks in such a way as to ensure that each task’s specific timing constraints are met. However, the current implementation does not work well on asymmetric CPU configurations like Arm’s big.LITTLE. Dietmar Eggemann recently posted a patch set to address this problem by adding the notion of CPU capacity to the deadline scheduler.
We are living through interesting times that present challenges in a number of areas, including running a business. While we think of LWN primarily as a community resource, it is also a business that is not unaffected by the ongoing pandemic. It is, we figure, a good time for a status update, especially since we have some news to share.
The OpenSSH 8.3 release is out. This primarily a bug-fix release with a handful of minor new features. It does, however, carry a prominent notice that ssh-rsa signature algorithm will be disabled in “a near-future release“. The announcement includes information on how to determine whether hosts you care about are affected.
Here’s a detailed blog entry from Dan Carpenter on adding improved lock checking to the smatch static-analysis tool. “When Smatch gained the ability to do cross function analysis in 2010, I knew that I had to re-write the locking check to take advantage of the new cross function analysis feature. When you combine cross function analysis with top of the line flow analysis available and in depth knowledge of kernel locks then the result is the Ultimate Locking Check! Unfortunately, I have a tendency towards procrastination and it took me a decade to get around to it, but it is done now. This blog will step through how the locking analysis works.”
Version 017 of the decidedly non-traditional GoboLinux distribution has been released. “This release introduces a simplified model for recipe management and contribution that’s fully integrated with the Compile build tool.
The recipe tree is now a plain Git repository managed via GitHub cloned into your /Data/Compile/Recipes directory and used by the GoboLinux Compile tool directly.”
Hibernation is normally thought of as a laptop feature — and an old and obsolete laptop feature at that. One does not normally consider it to be relevant in cloud settings. But, at the 2020 Power Management and Scheduling in the Linux Kernel summit (OSPM), Andrea Righi argued that there may actually be a place for hibernation on cloud-based systems if it can be made to work reliably.
The 5.7-rc7 kernel prepatch is out. “So it looks like I was worried for nothing last rc. Of course, anything can still change, but everything _looks_ all set for a regular release scheduled for next weekend. Knock wood.”
The kernel’s CPU scheduler is good at distributing tasks across a multiprocessor system, but does it do so fairly? If some tasks get a lot more CPU time than others, the result is likely to be unhappy users. Vincent Guittot ran a session at the 2020 Power Management and Scheduling in the Linux Kernel summit (OSPM) looking into this issue, with a focus on detecting load imbalances between CPUs and what to do with a workload that cannot be balanced.
As Rafael Wysocki conceded at the beginning of a session at the 2020 Power Management and Scheduling in the Linux Kernel summit (OSPM), the combination of the deadline scheduling class with CPU idle states might seem a little strange. Deadline scheduling is used in realtime settings, where introducing latency by idling the CPU tends to be frowned upon. But there are reasons to think that these two technologies might just be made to work together.
Frequency scaling — adjusting a CPU’s operating frequency to save power when the workload demands are low — is common practice across systems supported by Linux. It is, however, viewed with some suspicion in data-center settings, where power consumption is less of a concern and there is a strong emphasis on getting the most performance out of the hardware. At the 2020 Power Management and Scheduling in the Linux Kernel summit (OSPM), Giovanni Gherdovich worried that frequency scaling may be about to go extinct in data centers; he made a plea for improving its behavior for such workloads while there is still time.
The purpose of a cpuidle governor is to decide which idle state a CPU should go into when it has no useful work to do; the cpuidle driver then actually puts the CPU into that state. But, at the 2020 Power Management and Scheduling in the Linux Kernel summit (OSPM), Abhishek Goel presented a new cpuidle driver that doesn’t actually change the processor’s power state at all. Such a driver will clearly save no power, but it can be quite useful as a tool for evaluating and debugging cpuidle policies.
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