LWN on Linux Kernel: Scheduler, Speck, and WireGuard
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Scheduler utilization clamping
Once upon a time, the only way to control how the kernel's CPU scheduler treated any given process was to adjust that process's priority. Priorities are no longer enough to fully control CPU scheduling, though, especially when power-management concerns are taken into account. The utilization clamping patch set from Patrick Bellasi is the latest in a series of attempts to allow user space to tell the scheduler more about any specific process's needs.
Contemporary CPU schedulers have a number of decisions to make at any given time. They must, of course, pick the process that will be allowed to execute in each CPU on the system, distributing processes across those CPUs to keep the system as a whole in an optimal state of busyness. Increasingly, the scheduler is also involved in power management — ensuring that the CPUs do not burn more energy than they have to. Filling that role requires placing each process on a CPU that is appropriate for that process's needs; modern systems often have more than one type of CPU available. The scheduler must also pick an appropriate operating power point — frequency and voltage — for each CPU to enable it to run the workload in a timely manner while minimizing energy consumption.
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Reconsidering Speck
The Speck cipher is geared toward good performance in software, which makes it attractive for smaller, often embedded, systems with underpowered CPUs that lack hardware crypto acceleration. But it also comes from the US National Security Agency (NSA), which worries lots of people outside the US—and, in truth, a fair number of US citizens as well. The NSA has earned a reputation for promulgating various types of cryptographic algorithms with dubious properties. While the technical arguments against Speck, which is a fairly simple and straightforward algorithm with little room for backdoors, have not been all that compelling, the political arguments are potent—to the point where it is being dropped by the main proponent for including it in the kernel.
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WireGuarding the mainline
The WireGuard VPN tunnel has been under development — and attracting attention — for a few years now; LWN ran a review of it in March. While WireGuard can be found in a number of distribution repositories, it is not yet shipped with the mainline kernel because its author, Jason Donenfeld, hasn't gotten around to proposing it for upstreaming. That changed on on July 31, when Donenfeld posted WireGuard for review. Getting WireGuard itself into the mainline would probably not be all that hard; merging some of the support code it depends on could be another story, though.
WireGuard implements a simple tunneling protocol allowing network traffic to be routed through a virtual private network provider. It has been developed with an eye toward smallness, ease of verification, and performance, rather than large numbers of features. It is, according to the patch posting, "used by some massive companies pushing enormous amounts of traffic". Some effort has gone into making WireGuard widely available, an effort that has helped to create a significant user community. But the ultimate way to make this kind of software widely available is to get it into everybody's kernel; that requires upstreaming.
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