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.
And move related ops into it. This is a bit more natural and will also allow
doing other operaitons (e.g. describing stats) without launching the server.
Make `--primar-domain auto` aware of turbo boosted CPUs and prioritize
them over the primary scheduling domain when the energy model
`balance_power` is used (typically when running on battery power with
the "balanced" profile).
With this change the scheduling hierarchy becomes the following:
1) CPUs in the turbo scheduling domain
2) CPUs in the primary scheduling domain
3) full-idle SMT CPUs
4) CPUs in the same L2 cache
5) CPUs in the same L3 cache
6) CPUs in the task's allowed domain
And the idle selection logic is modified as following:
- In the turbo scheduling domain:
- pick same full-idle SMT CPU
- pick any other full-idle SMT CPU sharing the same L2 cache
- pick any other full-idle SMT CPU sharing the same L3 cache
- pick any other full-idle SMT CPU
- pick same idle CPU
- pick any other idle CPU sharing the same L2 cache
- pick any other idle CPU sharing the same L3 cache
- pick any other idle SMT CPU
- In the primary scheduling domain:
- pick same full-idle SMT CPU
- pick any other full-idle SMT CPU sharing the same L2 cache
- pick any other full-idle SMT CPU sharing the same L3 cache
- pick any other full-idle SMT CPU
- pick same idle CPU
- pick any other idle CPU sharing the same L2 cache
- pick any other idle CPU sharing the same L3 cache
- pick any other idle SMT CPU
- In the entire task domain:
- pick any other idle CPU
Keep in mind that the turbo domain will be evaluated only when the
scheduler is started with `--primary-domain auto` and only when the
`balance_power` energy profile is used.
The turbo domain is always made using the subset of CPUs in the system
with the highest max frequency. If such subset can't be determined (for
example if all the CPUs in the primary domain have all the same
frequency), the turbo domain will be ignored.
Prioritizing turbo boosted CPUs can help to improve performance by
forcing the governor to scale up their frequency, without increasing too
much power consumption, due to the fact that tasks will be preferably
confined into a reduced amount of cores.
This change seems to improve performance, without increasing much
power consuption, on Intel laptops while using the `balanced_power`
energy profile.
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
Introduce the new option `--primary-domain auto`. With this option the
scheduler will dynamically adjusts the primary scheduling domain at
run-time, in function of the current energy profile reported in
/sys/devices/system/cpu/cpufreq/policy0/energy_performance_preference.
When the `power` energy profile is selected, the primary scheduling
domain will prioritize E-cores. Alternatively, when the `performance`
profile is selected, it will prioritize P-cores. For all the other
energy profiles, all the CPUs in the system will be used.
Note that this option is only relevant on hybrid architectures with
P-cores and E-cores.
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
OM labels() was called with an array which is then incorrectly interpreted
as a single label. Unpack it to list of arguments. While at it, make error
reporting a bit more robust.
