Introduce the new `--lowlatency` option, which enables switching between
the default pure vruntime-based scheduling (more optimized for server
workloads) and a deadline-based scheduling (better suited for
low-latency workloads).
When the low-latency mode is activated, a task's deadline is calculated
as its vruntime, adjusted by a bonus proportional to the task's average
number of voluntary context switches (the more voluntary context
switches, the shorter the deadline).
This feature enhances the prioritization of interactive tasks even more,
proportionally to their average voluntary context switches, also within
the two main global queues (priority / shared) and it helps to maintain
interactive workloads always responsive, even in presence of heavy
non-interactive background work.
Low-latency mode allows to prevent audio cracking even in presence of a
large amount of short-lived tasks with pseudo-interactive behavior (i.e,
hackbench) and it enables achieving approximately a +33% average
frames-per-second (FPS) in the typical "gaming while building the
kernel" benchmark.
However, it can also amplify the de-prioritization of CPU-intensive
tasks, making this option more suitable for specific low-latency
scenarios. Therefore the low-latency mode is disabled by default and it
can only be enabled via the `--lowlatency` option.
Tested-by: Piotr Gorski (piotrgorski@cachyos.org)
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
Explicitly replenish the task's time slice from ops.dispatch() if the
task still wants to run and no other task is selected. In this way the
sched_ext core won't automatically re-schedule the task on the same CPU,
implicitly assigning a time slice of SCX_SLICE_DFL.
Moreover, 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 allows to use a more precise time slice, adjusted based on the
actual amount of tasks that are currently waiting to be scheduled.
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
The meaning of SCX_OPS_ENQ_LAST will change with future kernel updates and
enqueueing on local DSQ will no longer be sufficient to avoid stalls. No
reason to do it anyway. Just drop it.
With the global scx_utils::NR_CPU_IDS we don't need Topology anymore in
init_primary_domain(), so drop the variable to fix the following build
warning:
warning: unused variable: `topo`
--> src/main.rs:385:9
|
385 | topo: &Topology,
| ^^^^ help: if this is intentional, prefix it with an underscore: `_topo`
|
= note: `#[warn(unused_variables)]` on by default
Fixes: 1da249f ("scx_utils::topology: Always use NR_CPU_IDS and NR_CPUS_POSSIBLE")
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
LazyLock is stable but has become so only very recently and can trigger
build errors on not-too-old stable rustc's which are still in wide use.
Let's use lazy_static instead for now.
Signed-off-by: Tejun Heo <tj@kernel.org>
Use the base frequency, instead of maximum frequency, to classify fast
and slow CPUs. This ensures accurate distinction between Intel Turbo
Boost CPUs and genuinely faster CPUs when auto-detecting the primary
scheduling domain.
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
With Intel Turbo Boost enabled, some CPUs might show a higher maximum
frequency than others, even if they are not actually faster cores. This
can potentially confuse some auto-detection logic for distinguishing
between fast and slow cores in certain schedulers.
The base CPU frequency reported in
/sys/devices/system/cpu/cpuN/cpufreq/base_frequency represents a more
reliable indicator for identifying truly fast and slow cores.
To address this, provide a new base_freq() method in the struct Cpu,
which will return the base operational frequency of a CPU when Turbo
Boost is present. If Turbo Boost is not available, base_freq() will
return the maximum frequency, functioning the same as max_freq().
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
- Add static NR_CPU_IDS and NR_CPUS_POSSIBLE to topology.
- Fix comment for Topology::nr_cpu_ids(). Was missing a negation.
- cpumaks should be sized by nr_cpus_ids, not num_possible_cpus and the
number can't change while the system is running. Drop cpumask.nr_cpus and
use *NR_CPU_IDS everywhere.
- Update scx_utils/build.rs so that 12 char SHA1 is generated instead of
full one.
- Add --version to scx_rusty. Use custom one as we don't want to use the
default cargo version one.
Tasks enqueued with SCX_ENQ_WAKEUP are immediately classified as
interactive. However, if interactive tasks classification is disabled
(via `-c 0`), we should avoid promoting them as interactive.
This is particularly important because, with the nvcsw logic disabled,
tasks can remain classified as interactive indefinitely and they will
never be demoted to regular tasks.
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
Rely on scx_utils::Cpumask instead of re-implementing a custom struct to
parse and manage CPU masks.
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
Allow to format a Cpumask as an hex string, implementing the proper
formatter LowerHex / UpperHex traits.
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
Fix a bug introduced in #510 where it assumed core ids are incremental.
This refactors the core ordering for layers to be far more simple and
provide some space for layer core isolation in low utilization.
Signed-off-by: Daniel Hodges <hodges.daniel.scott@gmail.com>
Rely on scx_utils::Topology to get CPU and cache information, instead of
re-implementing custom methods.
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
Add the L2 / L3 cache id to the Cpu struct, to quickly determine the
cache nodes associated to each CPU.
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
scx_layered now can be run with a single command when `--run-example` is
specified. Update test_sched script to support per-sched arguments and
enable it for scx_layered.
