In line with rustland's focus on prioritizing interactive tasks, set the
default base time slice to 5ms.
This allows to mitigate potential audio craking issues or system lags
when the system is overloaded or under memory pressure condition (i.e.,
https://github.com/sched-ext/scx/issues/96#issuecomment-1978154324).
A downside of this change is to introduce potential regressions in the
throughput of CPU-intensive workloads, but in such scenarios rustland
may not be the optimal choice and alternative schedulers may be
preferred.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Some high-priority tasks may have a weight too high, that can
potentially disrupt the slice boost optimization logic, causing
interactive tasks to be less responsive.
In line with rustland's focus on prioritizing interactive tasks, prevent
giving too much CPU bandwidth to such high-priority tasks by limiting
the maximum task weight to 1000.
This allows to maintain a good level of system responsiveness even in
presence of tasks with a really high priority.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Use the new consume_raw() API provided by libbpf-rs with
https://github.com/libbpf/libbpf-rs/pull/680.
This allows to be more precise and efficient at processing tasks
consumed from the BPF ring buffer.
NOTE: the new consume_raw() API is not available yet in any official
release of the libbpf-rs crate, but cargo allows to pick versions
directly from git. This slightly increases the build time of
scx_rustland_core and the schedulers based on this crate (since we need
to recompile libbpf-rs from source), but we can re-add a proper
versioned dependency once the libbpf-rs is out.
TODO: this new API also offers the possibility to consume multiple items
from the BPF ring buffer with a single call to consume_raw(). This could
be investigated and implemented as a potential future enhancement.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Instead clone the libbpf repo at a specific hash during setup.
This is to fix an issue whereby submodules are not included
in the tarball and therefore won't be updated/fetched during
setup after unzipping the tarball.
This is to fix an error sometimes seen when compiling with gcc,
whereby the position independent sched ext rust libraries
don't play nicely with the libbpf library if it's not also built
as position independent.
This also explicitly sets the rustc relocation-mode to "pic",
which is the default (just so this doesn't accidentally change
out from under us).
scx_rlfifo is provided as a simple example to show how to use
scx_rustland_core and it's not supposed to be used in a real production
environment.
To prevent performance bug reports print an explicit warning when it's
started to clarify the goal of this scheduler.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Small improvement to make the scheduler a bit more responsive, without
introducing too much complexity or too much CPU overhead.
This can be achieved by replacing a sleep of 1ms with a sched_yield()
every time that the scheduler has finished to dispatch all the queued
tasks.
This also makes the code a bit smaller and easier to read.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Otherwise, we end up passing CC=ccache to libbpf's Makefile which triggers
an error as ccache invoked on its own can't act as a stand-in for the
compiler.
Provide distinct methods to set the target CPU and the per-task time
slice to dispatched tasks.
Moreover, also provide a constructor to create a DispatchedTask from a
QueuedTask (this allows to automatically bounce a task from the
scheduler to the BPF dispatcher without having to take care of setting
the individual task's attributes).
This also allows to make most of the attributes of DispatchedTask
private, especially it allows to hide cpumask_cnt, that should be only
used internally between the BPF and the user-space component.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Provide a way to set a different time slice per-task, by adding a new
attribute slice_ns to the DispatchedTask struct.
This attribute determines the time slice assigned to the task, if it is
set to 0 then the global time slice (either the default one or the
effective one, if set) will be used.
At the same time, remove the payload attribute, that is basically unused
(scx_rustland uses it to send the task's vruntime to the BPF dispatcher
for debugging purposes, but it's not very useful anymore at this point).
In the future we may introduce a proper interface to attach a custom
payload to each task with a proper interface.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
This is to potentinally reduce issues with folks
using different versions of libbpf at runtime.
This also:
- makes static linking of libbpf the default
- adds steps in `meson setup` to fetch libbpf and make it
This reverts commit a7b39f24e2, reversing
changes made to cf7404fb03.
The PR doesn't do what the description says. It instead limits the number of
rustc instances to 1 for each cargo build making rust builds extremely slow.
Let's revert and try again.
This reverts commit 5b9b953e3c, reversing
changes made to a7b39f24e2.
The current git submodule approach is a bit cumbersome and doesn't provide a
unified build environment for both libbpf and scx scheds. Also, the build
instruction doesn't seem to work. Let's revert it for now.
Each cargo build is already parallelized, spreading multiple rustc
across all the available CPUs by default.
Allowing to run multiple instances of cargo at the same time doesn't
provide any benefit and it can only increase the risk of triggering OOM
conditions or overloading the build system.
Therefore, limit the amount of parallel cargo build instances to 1.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
There is no need to generate source code in a temporary directory with
RustLandBuilder(), we can simply generate code in-tree and exclude the
generated source files from .gitignore.
Having the generated source files in-tree can help to debug potential
build issues (and it also allows to drop the the tempfile crate
dependency).
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Introduce a Builder() class in scx_utils that can be used by other scx
crates (such as scx_rustland_core) to prevent code duplication.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Introduce a wrapper to scx_utils::BpfBuilder that can be used to build
the BPF component provided by scx_rustland_core.
The source of the BPF components (main.bpf.c) is included in the crate
as an array of bytes, the content is then unpacked in a temporary file
to perform the build.
The RustLandBuilder() helper is also used to generate bpf.rs (that
implements the low-level user-space Rust connector to the BPF
commponent).
Schedulers based on scx_rustland_core can simply use RustLandBuilder(),
to build the backend provided by scx_rustland_core.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Introduce a helper function to update the counter of queued and
scheduled tasks (used to notify the BPF component if the user-space
scheduler has still some pending work to do).
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
scx_rustland has significantly evolved since its original design.
With the introduction of scx_rustland_core and the inclusion of the
scx_rlfifo example, scx_rustland's focus can be shifted from solely
being an "easy-to-read Rust scheduler template" to a fully functional
scheduler.
For this reason, update the README and documentation to reflect its
revised design, objectives, and intended use cases.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Move the BPF component of scx_rustland to scx_rustland_core and make it
available to other user-space schedulers.
NOTE: main.bpf.c and bpf.rs are not pre-compiled in the
scx_rustland_core crate, they need to be included in the user-space
scheduler's source code in order to be compiled/linked properly.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Introduce a separate crate (scx_rustland_core) that can be used to
implement sched-ext schedulers in Rust that run in user-space.
This commit only provides the basic layout for the new crate and the
abstraction to the custom allocator.
In general, any scheduler that has a user-space component needs to use
the custom allocator to prevent potential deadlock conditions, caused by
page faults (a kthread needs to run to resolve the page fault, but the
scheduler is blocked waiting for the user-space page fault to be
resolved => deadlock).
However, we don't want to necessarily enforce this constraint to all the
existing Rust schedulers, some of them may do all user-space allocations
in safe paths, hence the separate scx_rustland_core crate.
Merging this code in scx_utils would force all the Rust schedulers to
use the custom allocator.
In a future commit the scx_rustland backend will be moved to
scx_rustland_core, making it a totally generic BPF scheduler framework
that can be used to implement user-space schedulers in Rust.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
