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sched_ext: Rename scx_bpf_dispatch[_vtime]() to scx_bpf_dsq_insert[_vtime]()

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In sched_ext API, a repeatedly reported pain point is the overuse of the
verb "dispatch" and confusion around "consume":

- ops.dispatch()
- scx_bpf_dispatch[_vtime]()
- scx_bpf_consume()
- scx_bpf_dispatch[_vtime]_from_dsq*()

This overloading of the term is historical. Originally, there were only
built-in DSQs and moving a task into a DSQ always dispatched it for
execution. Using the verb "dispatch" for the kfuncs to move tasks into these
DSQs made sense.

Later, user DSQs were added and scx_bpf_dispatch[_vtime]() updated to be
able to insert tasks into any DSQ. The only allowed DSQ to DSQ transfer was
from a non-local DSQ to a local DSQ and this operation was named "consume".
This was already confusing as a task could be dispatched to a user DSQ from
ops.enqueue() and then the DSQ would have to be consumed in ops.dispatch().
Later addition of scx_bpf_dispatch_from_dsq*() made the confusion even worse
as "dispatch" in this context meant moving a task to an arbitrary DSQ from a
user DSQ.

Clean up the API with the following renames:

1. scx_bpf_dispatch[_vtime]()		-> scx_bpf_dsq_insert[_vtime]()
2. scx_bpf_consume()			-> scx_bpf_dsq_move_to_local()
3. scx_bpf_dispatch[_vtime]_from_dsq*()	-> scx_bpf_dsq_move[_vtime]*()

This patch performs the first set of renames. Compatibility is maintained
by:

- The previous kfunc names are still provided by the kernel so that old
  binaries can run. Kernel generates a warning when the old names are used.

- compat.bpf.h provides wrappers for the new names which automatically fall
  back to the old names when running on older kernels. They also trigger
  build error if old names are used for new builds.

The compat features will be dropped after v6.15.

v2: Documentation updates.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Andrea Righi <arighi@nvidia.com>
Acked-by: Changwoo Min <changwoo@igalia.com>
Acked-by: Johannes Bechberger <me@mostlynerdless.de>
Acked-by: Giovanni Gherdovich <ggherdovich@suse.com>
Cc: Dan Schatzberg <dschatzberg@meta.com>
Cc: Ming Yang <yougmark94@gmail.com>
This commit is contained in:
Tejun Heo
2024-11-11 07:06:16 -10:00
parent 72b85bf6a7
commit cc26abb1a1
8 changed files with 144 additions and 97 deletions
Download Patch File Download Diff File Expand all files Collapse all files

50
Documentation/scheduler/sched-ext.rst
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@@ -130,7 +130,7 @@ optional. The following modified excerpt is from
* Decide which CPU a task should be migrated to before being
* enqueued (either at wakeup, fork time, or exec time). If an
* idle core is found by the default ops.select_cpu() implementation,
* then dispatch the task directly to SCX_DSQ_LOCAL and skip the
* then insert the task directly into SCX_DSQ_LOCAL and skip the
* ops.enqueue() callback.
*
* Note that this implementation has exactly the same behavior as the
@@ -148,15 +148,15 @@ optional. The following modified excerpt is from
cpu = scx_bpf_select_cpu_dfl(p, prev_cpu, wake_flags, &direct);
if (direct)
scx_bpf_dispatch(p, SCX_DSQ_LOCAL, SCX_SLICE_DFL, 0);
scx_bpf_dsq_insert(p, SCX_DSQ_LOCAL, SCX_SLICE_DFL, 0);
return cpu;
}
/*
* Do a direct dispatch of a task to the global DSQ. This ops.enqueue()
* callback will only be invoked if we failed to find a core to dispatch
* to in ops.select_cpu() above.
* Do a direct insertion of a task to the global DSQ. This ops.enqueue()
* callback will only be invoked if we failed to find a core to insert
* into in ops.select_cpu() above.
*
* Note that this implementation has exactly the same behavior as the
* default ops.enqueue implementation, which just dispatches the task
@@ -166,7 +166,7 @@ optional. The following modified excerpt is from
*/
void BPF_STRUCT_OPS(simple_enqueue, struct task_struct *p, u64 enq_flags)
{
scx_bpf_dispatch(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL, enq_flags);
scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL, enq_flags);
}
s32 BPF_STRUCT_OPS_SLEEPABLE(simple_init)
@@ -202,7 +202,7 @@ 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
``scx_bpf_destroy_dsq()``.
A CPU always executes a task from its local DSQ. A task is "dispatched" to a
A CPU always executes a task from its local DSQ. A task is "inserted" into a
DSQ. A non-local DSQ is "consumed" to transfer a task to the consuming CPU's
local DSQ.
@@ -229,26 +229,26 @@ The following briefly shows how a waking task is scheduled and executed.
scheduler can wake up any cpu using the ``scx_bpf_kick_cpu()`` helper,
using ``ops.select_cpu()`` judiciously can be simpler and more efficient.
A task can be immediately dispatched to a DSQ from ``ops.select_cpu()`` by
calling ``scx_bpf_dispatch()``. If the task is dispatched to
``SCX_DSQ_LOCAL`` from ``ops.select_cpu()``, it will be dispatched to the
A task can be immediately inserted into a DSQ from ``ops.select_cpu()``
by calling ``scx_bpf_dsq_insert()``. If the task is inserted into
``SCX_DSQ_LOCAL`` from ``ops.select_cpu()``, it will be inserted into the
local DSQ of whichever CPU is returned from ``ops.select_cpu()``.
Additionally, dispatching directly from ``ops.select_cpu()`` will cause the
Additionally, inserting directly from ``ops.select_cpu()`` will cause the
``ops.enqueue()`` callback to be skipped.
Note that the scheduler core will ignore an invalid CPU selection, for
example, if it's outside the allowed cpumask of the task.
2. Once the target CPU is selected, ``ops.enqueue()`` is invoked (unless the
task was dispatched directly from ``ops.select_cpu()``). ``ops.enqueue()``
task was inserted directly from ``ops.select_cpu()``). ``ops.enqueue()``
can make one of the following decisions:
* Immediately dispatch the task to either the global or local DSQ by
calling ``scx_bpf_dispatch()`` with ``SCX_DSQ_GLOBAL`` or
* Immediately insert the task into either the global or local DSQ by
calling ``scx_bpf_dsq_insert()`` with ``SCX_DSQ_GLOBAL`` or
``SCX_DSQ_LOCAL``, respectively.
* Immediately dispatch the task to a custom DSQ by calling
``scx_bpf_dispatch()`` with a DSQ ID which is smaller than 2^63.
* Immediately insert the task into a custom DSQ by calling
``scx_bpf_dsq_insert()`` with a DSQ ID which is smaller than 2^63.
* Queue the task on the BPF side.
@@ -257,11 +257,11 @@ The following briefly shows how a waking task is scheduled and executed.
run, ``ops.dispatch()`` is invoked which can use the following two
functions to populate the local DSQ.
* ``scx_bpf_dispatch()`` dispatches a task to a DSQ. Any target DSQ can
be used - ``SCX_DSQ_LOCAL``, ``SCX_DSQ_LOCAL_ON | cpu``,
``SCX_DSQ_GLOBAL`` or a custom DSQ. While ``scx_bpf_dispatch()``
* ``scx_bpf_dsq_insert()`` inserts a task to a DSQ. Any target DSQ can be
used - ``SCX_DSQ_LOCAL``, ``SCX_DSQ_LOCAL_ON | cpu``,
``SCX_DSQ_GLOBAL`` or a custom DSQ. While ``scx_bpf_dsq_insert()``
currently can't be called with BPF locks held, this is being worked on
and will be supported. ``scx_bpf_dispatch()`` schedules dispatching
and will be supported. ``scx_bpf_dsq_insert()`` schedules insertion
rather than performing them immediately. There can be up to
``ops.dispatch_max_batch`` pending tasks.
@@ -288,12 +288,12 @@ built-in DSQs are used, there is no need to implement ``ops.dispatch()`` as
a task is never queued on the BPF scheduler and both the local and global
DSQs are consumed automatically.
``scx_bpf_dispatch()`` queues the task on the FIFO of the target DSQ. Use
``scx_bpf_dispatch_vtime()`` for the priority queue. Internal DSQs such as
``scx_bpf_dsq_insert()`` inserts the task on the FIFO of the target DSQ. Use
``scx_bpf_dsq_insert_vtime()`` for the priority queue. Internal DSQs such as
``SCX_DSQ_LOCAL`` and ``SCX_DSQ_GLOBAL`` do not support priority-queue
dispatching, and must be dispatched to with ``scx_bpf_dispatch()``. See the
function documentation and usage in ``tools/sched_ext/scx_simple.bpf.c`` for
more information.
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.
Where to Look
=============