sched_ext: idle: Accept an arbitrary cpumask in scx_select_cpu_dfl()

Browse source

Many scx schedulers implement their own hard or soft-affinity rules
to support topology characteristics, such as heterogeneous architectures
(e.g., big.LITTLE, P-cores/E-cores), or to categorize tasks based on
specific properties (e.g., running certain tasks only in a subset of
CPUs).

Currently, there is no mechanism that allows to use the built-in idle
CPU selection policy to an arbitrary subset of CPUs. As a result,
schedulers often implement their own idle CPU selection policies, which
are typically similar to one another, leading to a lot of code
duplication.

To address this, modify scx_select_cpu_dfl() to accept an arbitrary
cpumask, that can be used by the BPF schedulers to apply the existent
built-in idle CPU selection policy to a subset of allowed CPUs.

With this concept the idle CPU selection policy becomes the following:
 - always prioritize CPUs from fully idle SMT cores (if SMT is enabled),
 - select the same CPU if it's idle and in the allowed CPUs,
 - select an idle CPU within the same LLC, if the LLC cpumask is a
   subset of the allowed CPUs,
 - select an idle CPU within the same node, if the node cpumask is a
   subset of the allowed CPUs,
 - select an idle CPU within the allowed CPUs.

This functionality will be exposed through a dedicated kfunc in a
separate patch.

Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

...

This commit is contained in:

Andrea Righi 2025-04-05 15:39:23 +02:00 • committed by Tejun Heo

parent 23c63a9652

commit c2d8b2a57c

1 changed files with 44 additions and 4 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

48

kernel/sched/ext_idle.c

View file