17 docs tagged with "scheduling"

The pinned kernel for this section, v6.18, does not run CFS as its fair-class scheduler — it runs

Everything earlier in this folder schedules tasks. A container, a service, or a user session is a

The method has to come before any tool. "The application is janky" is not a scheduling problem until you

CFS and Virtual Runtime ended on a specific complaint: CFS had exactly one

When the kernel is executing on behalf of a task — running a system call, handling a fault, walking a

What does nice -n 5 actually buy a process? Not a percentage, and not a guarantee — and, despite the

The word misleads, so the definition has to come first: real-time does not mean fast. It means

How does one scheduler support real-time tasks, deadline tasks, ordinary tasks, and the idle task all at

There are almost always more runnable threads than CPU cores. The scheduler is the kernel

Most firmware priority assignments are opinions. Somebody decided the safety task was the most important thing in the system and gave it the highest priority, somebody else discovered the display flickered and bumped its task up, and three years later nobody can say whether the 1 kHz control loop meets its deadline — only that it seems to. Real-time scheduling theory replaces that with arithmetic. Given each task's execution time, its period and its deadline, it answers "does every task always meet its deadline" with a proof rather than a measurement campaign.

The load balancer lives in a permanent tension. Moving a runnable task onto an idle CPU puts otherwise

A task looks like an infinite loop written as if it owned the processor. That illusion is the whole product, and it is manufactured from three things: a block of RAM used as a stack, a small structure recording where that stack's pointer got to, and membership of exactly one linked list. Everything the scheduler does is move that structure between lists.

A context switch is both smaller and larger than people think. The part with a name — saving one

Every embedded program is an infinite loop. The interesting question is what is inside it. A while(1) that calls three functions in order is the simplest architecture that can run a device, it ships in an enormous number of products, and it is entirely capable of being the right answer for the lifetime of a project. It is also the architecture that fails most quietly when it stops being the right answer, because nothing breaks — the loop just gets slower, and one day a button press is dropped.

Every SIMT behavior that looks unusual coming from CPU threading — coalescing, divergence, the fact that occupancy is measured in resident warps rather than resident threads — traces back to one hardware fact what it decides among, how fast it can issue, and how to read its behavior back out of a profiler.

"The scheduler" is not one algorithm answering one question. It answers three: which runnable task

An RTOS does not make anything faster. It runs the same instructions on the same core at the same clock, and it adds work — a tick interrupt, a scheduler, a context switch — so a system that adopts one gets strictly less CPU time for its application. Anybody selling a kernel on performance is selling the wrong thing.