meson build script was building each rust sub-project under rust/ and
scheds/rust/ separately. This means that each rust project is built
independently which leads to a couple problems - 1. There are a lot of
shared dependencies but they have to be built over and over again for each
proejct. 2. Concurrency management becomes sad - we either have to unleash
multiple cargo builds at the same time possibly thrashing the system or
build one by one.
We've been trying to solve this from meson side in vain. Thankfully, in
issue #546, @vimproved suggested using cargo workspace which makes the
sub-projects share the same target directory and built together by the same
cargo instance while still allowing each project to behave independently for
development and publishing purposes.
Make the following changes:
- Create two cargo workspaces - one under rust/, the other under
scheds/rust/. Each contains all rust projects underneath it.
- Don't let meson descend into rust/. These are libraries used by the rust
schedulers. No need to build them from meson. Cargo will build them as
needed.
- Change the rust_scheds build target to invoke `cargo build` in
scheds/rust/ and let cargo do its thing.
- Remove per-scheduler meson.build files and instead generate custom_targets
in scheds/rust/meson.build which invokes `cargo build -p $SCHED`.
- This changes rust binary directory. Update README and
meson-scripts/install_rust_user_scheds accordingly.
- Remove per-scheduler Cargo.lock as scheds/rust/Cargo.lock is shared by all
schedulers now.
- Unify .gitignore handling.
The followings are build times on Ryzen 3975W:
Before:
________________________________________________________
Executed in 165.93 secs fish external
usr time 40.55 mins 2.71 millis 40.55 mins
sys time 3.34 mins 36.40 millis 3.34 mins
After:
________________________________________________________
Executed in 36.04 secs fish external
usr time 336.42 secs 0.00 millis 336.42 secs
sys time 36.65 secs 43.95 millis 36.61 secs
Wallclock time is reduced 5x and CPU time 7x.
Refactor the code to hide the shutdown handling inside BpfScheduler and
simply use the exited() method to check when the scheduler is stopped.
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
Three of the reported stats are cumulative. While they obviously can be
processed into delta values, that holds for the other direction too and the
cumulative values are difficult to make intutive sense of. Report interval
delta values instead.
Note that a stats client can reliably build back cumulative values even
under heavy system contention - the delta values reported between two
consecutive reads are guaranteed to be correct regardless of the duration of
the interval.
Use scx_stats instead of prometheus for stats reporting. This has a few
advantages:
- Stats metadata can be defined more succinctly.
- Natural support for nesting statistics which will be useful in making
scheduler components composable.
- Support for multiple programmable readers where each reader can use their
own reading interval.
- Built-in stats help message generation.
- Openmetrics integration is still available through
scx_stats/scripts/scxstats_to_openmetrics.py.
Let's make it a bit easier to use:
- Shorten exported names by changing the prefix from ScxStats to Stats. This
should be distinctive enough and more inline with how most libraries name
their exports.
- Importing the right set of traits can be tricky. Introduce prelude module
so that importing is a bit less painful.
There is no reason to have two separate options for "verbose" and
"debug" mode. Just merge the two and always use "debug". If enabled,
increase verbosity to stdout and enable reporting BPF scheduling events
in debugfs (e.g., /sys/kernel/debug/tracing/trace_pipe).
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
Since scx_rustland_core enables setting a time slice on a per-task basis
during task dispatch, there's no need to maintain a global time slice in
the BPF component. Instead, a global time slice can simply be managed in
user-space, achieving the same outcome.
Therefore, drop the global slice_us property from BpfScheduler to
simplify the API.
NOTE: if a time slice is not specified for a task, SCX_SLICE_DFL will be
used by default.
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
Add more comments to make the source code more understandable, so that
it can be easily used as a template for implementing more complex
scheduling policies.
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
Scheduling sample reporting is switched to use scx_stats. This makes the
scheduler run without making too much noise while still allowing monitoring
on demand. It can also make introspection more dynamic - e.g. it shouldn't
be difficult to add other monitoring commands which take scheduling samples
based on different criteria or add other types of staisitcs.
--nr_sched-samples is replaced with --monitor-nr-samples.
The update_tasks() API is somewhat confusing, so replace it with a
clearer API, notify_complete().
This new API will return control to the BPF component and inform it
about the number of tasks still pending in the user-space scheduler.
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
The low-power API is a bit of a hack implemented purely in the BPF
layer, this should be better re-implemented with some concepts of
topology awareness.
Therefore, get rid of this API for now.
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
The current API used to notify the user-space scheduler when a task
exits is really confusing (setting a negative value in
queued_task_ctx.cpu), and it's also possible to detect task exiting
events from user-space (or check in procfs, even if it's slower).
In any case, a better API should be provided for this, so drop the
current one for now.
NOTE: this will cause additional memory usage for scx_rustland, but it
can be fixed/addressed later in a separate commit (i.e., providing a
periodic garbage collector for the unused task entries).
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
Instead of determining the task time slice in ops.enqueue(), refresh the
time slice immediately before the task is started on its assigned CPU in
ops.running().
This ensures to apply the exact time slice specified by the user-space
scheduler and the sched_ext core will never implicitly dispatch tasks
using SCX_SLICE_DFL.
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
Allow user-space scheduler to pick an idle CPU via
self.bpf.select_cpu(pid, prev_task, flags), mimicking the BPF's
select_cpu() iterface.
Also remove the full_user option and always rely on the idle selection
logic from user-space.
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
Keep evaluating the average number of voluntary context switches for
each task when lowlatency mode is enabled, even when interactive tasks
classification is disabled (via `-c 0`).
The average nvcsw is also used in lowlatency mode to evaluate the
proportional bonus to the tasks' deadline and it shouldn't be ignored
when interactive tasks classification is disabled. Moreover, make sure
that such bonus never exceeds the starvation threshold.
Keep in mind that it is still possible to disable the periodic average
nvcsw evaluation with `-c 0`, without specifying `--lowlatency`.
Fixes: 6a22853 ("scx_bpfland: introduce --lowlatency option")
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
A lot of scx_lavd's options do not clearly explain what they do. Add
some short explanations, clean up the existing ones, and direct the user
to read the in-code documentation for more info.
