Provide the following primitives to get and set CPU ownership in the BPF
part. This improves code readability and these primitives can be used by
the BPF part as a baseline to implement a better CPU idle tracking in
the future.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
BPF doesn't have full memory model yet, and while strict atomicity might
not be necessary in this context, it is advisable to enhance clarity in
the interlocking model.
To achieve this, provide the following primitives to operate on
usersched_needed:
static void set_usersched_needed(void)
static bool test_and_clear_usersched_needed(void)
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Dispatch tasks in a batch equal to the amount of idle CPUs in the
system.
This allows to reduce the pressure on the dispatcher queues, improving
the effectiveness of the scheduler (by having more tasks sitting in the
scheduler task pool) and mitigating potential priority inversion issues.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Provide an interface for the BPF dispatcher and user-space scheduler to
share CPU information. This information can empower the user-space
scheduler to make more informed decisions and enable the implementation
of a broader range of scheduling policies.
With this change the BPF dispatcher provides a CPU map (one entry per
CPU) that stores the pid that is running on each CPU (0 if the CPU is
idle). The CPU map is updated by the BPF dispatcher in the .running()
and .stopping() callbacks.
The dispatcher then sends to the user-space scheduler a suggestion of
the candidate CPU for each task that needs to run (that is always the
previously used CPU), along with all the task's information.
The user-space scheduler can decide to confirm the selected CPU or to
choose a different one, using all the shared CPU information.
Lastly, the selected CPU is communicated back to the dispatcher along
with all the task's information and the BPF dispatcher takes care of
executing the task on the selected CPU, eventually triggering a
migration.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Do not report an exit error message if it's empty. Moreover, distinguish
between a graceful exit vs a non-graceful exit.
In general, try to follow the behavior of user_exit_info.h for the C
schedulers.
NOTE: in the future the whole exit handling probably can be moved to a
more generic place (scx_utils) to prevent code duplication across
schedulers and also to prevent small inconsistencies like this one.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Rename scx_rustlite to scx_rustland to better represent the mirroring of
scx_userland (in C), but implemented in Rust.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
This scheduler is made of a BPF component (dispatcher) that implements
the low level sched-ext functionalities and a user-space counterpart
(scheduler), written in Rust, that implements the actual scheduling
policy.
The main goal of this scheduler is to be easy to read and well
documented, so that newcomers (i.e., students, researchers, junior devs,
etc.) can use this as a template to quickly experiment scheduling
theory.
For this reason the design of this scheduler is mostly focused on
simplicity and code readability.
Moreover, the BPF dispatcher is completely agnostic of the particular
scheduling policy implemented by the user-space scheduler. For this
reason developers that are willing to use this scheduler to experiment
scheduling policies should be able to simply modify the Rust component,
without having to deal with any internal kernel / BPF details.
Future improvements:
- Transfer the responsibility of determining the CPU for executing a
particular task to the user-space scheduler.
Right now this logic is still fully implemented in the BPF part and
the user-space scheduler can only decide the order of execution of
the tasks, that significantly restricts the scheduling policies that
can be implemented in the user-space scheduler.
- Experiment the possibility to send tasks from the user-space
scheduler to the BPF dispatcher using a batch size, instead of
draining the task queue completely and sending all the tasks at once
every single time.
A batch size should help to reduce the overhead and it should also
help to reduce the wakeups of the user-space scheduler.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
- combine c and kernel-examples as it's confusing to have both
- rename 'rust-user' and 'c-user' to just 'rust' and 'c', which is simpler
- update and fix sync-to-kernel.sh
