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sched_ext: Documentation: Clarify time slice handling in task lifecycle 

It is not always obvious how a task's time slice can be refilled, either
explicitly from ops.dispatch() or automatically by the sched_ext core,
to skip subsequent ops.enqueue() and ops.dispatch() calls. This
typically happens when the task is the only one running on a CPU.

To make this behavior easier to understand, update the task lifecycle
diagram to explicitly document how time slice handling works in such
cases.

Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Andrea Righi 2025-06-09 18:23:42 +02:00 committed by Tejun Heo
parent 086ed90a64
commit 9465f44d2d
1 changed files with 8 additions and 3 deletions
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9
Documentation/scheduler/sched-ext.rst
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@ -313,16 +313,21 @@ by a sched_ext scheduler:
ops.runnable(); /* Task becomes ready to run */
while (task is runnable) {
if (task is not in a DSQ) {
if (task is not in a DSQ && task->scx.slice == 0) {
ops.enqueue(); /* Task can be added to a DSQ */
/* A CPU becomes available */
/* Any usable CPU becomes available */
ops.dispatch(); /* Task is moved to a local DSQ */
}
ops.running(); /* Task starts running on its assigned CPU */
while (task->scx.slice > 0 && task is runnable)
ops.tick(); /* Called every 1/HZ seconds */
ops.stopping(); /* Task stops running (time slice expires or wait) */
/* Task's CPU becomes available */
ops.dispatch(); /* task->scx.slice can be refilled */
}
ops.quiescent(); /* Task releases its assigned CPU (wait) */