sched_ext: Documentation: Clarify ops.dispatch() role in task lifecycle

ops.dispatch() is invoked when a CPU becomes available. This can occur
when a task voluntarily yields the CPU, exhausts its time slice, or is
preempted for other reasons.

If the task is still runnable, refilling its time slice in
ops.dispatch() (either by the BPF scheduler or the sched_ext core)
allows it to continue running without triggering ops.stopping().
However, this behavior is not clearly reflected in the current task
lifecycle diagram.

Update the diagram to better represent this interaction.

Fixes: 9465f44d2df2 ("sched_ext: Documentation: Clarify time slice handling in task lifecycle")
Cc: stable@vger.kernel.org # v6.17+
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 7 insertions, 5 deletions

diff --git a/Documentation/scheduler/sched-ext.rst b/Documentation/scheduler/sched-ext.rst
index 9e4dbabc03c0..404b4e4c33f7 100644
--- a/Documentation/scheduler/sched-ext.rst
+++ b/Documentation/scheduler/sched-ext.rst
@@ -433,13 +433,15 @@ by a sched_ext scheduler:
                 ops.dequeue(); /* Exiting BPF scheduler */
             }
             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 */
+            while task_is_runnable(p) {
+                while (task->scx.slice > 0 && task_is_runnable(p))
+                    ops.tick();     /* Called every 1/HZ seconds */
+
+                ops.dispatch();     /* task->scx.slice can be refilled */
+            }
 
-            ops.dispatch();     /* task->scx.slice can be refilled */
+            ops.stopping();     /* Task stops running (time slice expires or wait) */
         }
 
         ops.quiescent();        /* Task releases its assigned CPU (wait) */