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Diffstat (limited to 'Documentation/scheduler/sched-ext.rst')
| -rw-r--r-- | Documentation/scheduler/sched-ext.rst | 53 |
1 files changed, 45 insertions, 8 deletions
diff --git a/Documentation/scheduler/sched-ext.rst b/Documentation/scheduler/sched-ext.rst index c4672d7df2f7..a1869c38046e 100644 --- a/Documentation/scheduler/sched-ext.rst +++ b/Documentation/scheduler/sched-ext.rst @@ -1,3 +1,5 @@ +.. _sched-ext: + ========================== Extensible Scheduler Class ========================== @@ -47,8 +49,8 @@ options should be enabled to use sched_ext: sched_ext is used only when the BPF scheduler is loaded and running. If a task explicitly sets its scheduling policy to ``SCHED_EXT``, it will be -treated as ``SCHED_NORMAL`` and scheduled by CFS until the BPF scheduler is -loaded. +treated as ``SCHED_NORMAL`` and scheduled by the fair-class scheduler until the +BPF scheduler is loaded. When the BPF scheduler is loaded and ``SCX_OPS_SWITCH_PARTIAL`` is not set in ``ops->flags``, all ``SCHED_NORMAL``, ``SCHED_BATCH``, ``SCHED_IDLE``, and @@ -57,11 +59,11 @@ in ``ops->flags``, all ``SCHED_NORMAL``, ``SCHED_BATCH``, ``SCHED_IDLE``, and However, when the BPF scheduler is loaded and ``SCX_OPS_SWITCH_PARTIAL`` is set in ``ops->flags``, only tasks with the ``SCHED_EXT`` policy are scheduled by sched_ext, while tasks with ``SCHED_NORMAL``, ``SCHED_BATCH`` and -``SCHED_IDLE`` policies are scheduled by CFS. +``SCHED_IDLE`` policies are scheduled by the fair-class scheduler. Terminating the sched_ext scheduler program, triggering `SysRq-S`, or detection of any internal error including stalled runnable tasks aborts the -BPF scheduler and reverts all tasks back to CFS. +BPF scheduler and reverts all tasks back to the fair-class scheduler. .. code-block:: none @@ -107,8 +109,7 @@ detailed information: nr_rejected : 0 enable_seq : 1 -If ``CONFIG_SCHED_DEBUG`` is set, whether a given task is on sched_ext can -be determined as follows: +Whether a given task is on sched_ext can be determined as follows: .. code-block:: none @@ -198,8 +199,8 @@ Dispatch Queues To match the impedance between the scheduler core and the BPF scheduler, sched_ext uses DSQs (dispatch queues) which can operate as both a FIFO and a priority queue. By default, there is one global FIFO (``SCX_DSQ_GLOBAL``), -and one local dsq per CPU (``SCX_DSQ_LOCAL``). The BPF scheduler can manage -an arbitrary number of dsq's using ``scx_bpf_create_dsq()`` and +and one local DSQ per CPU (``SCX_DSQ_LOCAL``). The BPF scheduler can manage +an arbitrary number of DSQs using ``scx_bpf_create_dsq()`` and ``scx_bpf_destroy_dsq()``. A CPU always executes a task from its local DSQ. A task is "inserted" into a @@ -294,6 +295,42 @@ dispatching, and must be dispatched to with ``scx_bpf_dsq_insert()``. See the function documentation and usage in ``tools/sched_ext/scx_simple.bpf.c`` for more information. +Task Lifecycle +-------------- + +The following pseudo-code summarizes the entire lifecycle of a task managed +by a sched_ext scheduler: + +.. code-block:: c + + ops.init_task(); /* A new task is created */ + ops.enable(); /* Enable BPF scheduling for the task */ + + while (task in SCHED_EXT) { + if (task can migrate) + ops.select_cpu(); /* Called on wakeup (optimization) */ + + ops.runnable(); /* Task becomes ready to run */ + + while (task is runnable) { + if (task is not in a DSQ) { + ops.enqueue(); /* Task can be added to a DSQ */ + + /* A CPU becomes available */ + + ops.dispatch(); /* Task is moved to a local DSQ */ + } + ops.running(); /* Task starts running on its assigned CPU */ + ops.tick(); /* Called every 1/HZ seconds */ + ops.stopping(); /* Task stops running (time slice expires or wait) */ + } + + ops.quiescent(); /* Task releases its assigned CPU (wait) */ + } + + ops.disable(); /* Disable BPF scheduling for the task */ + ops.exit_task(); /* Task is destroyed */ + Where to Look ============= |