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sched_ext: idle: Honor idle flags in the built-in idle selection policy

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Enable passing idle flags (%SCX_PICK_IDLE_*) to scx_select_cpu_dfl(),
to enforce strict selection criteria, such as selecting an idle CPU
strictly within @prev_cpu's node or choosing only a fully idle SMT core.

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 2025-03-14 10:45:33 +01:00 committed by Tejun Heo
parent 97e13ecb02
commit c414c2171c
3 changed files with 32 additions and 13 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

2
kernel/sched/ext.c
View file

@ -3396,7 +3396,7 @@ static int select_task_rq_scx(struct task_struct *p, int prev_cpu, int wake_flag
bool found;
s32 cpu;
cpu = scx_select_cpu_dfl(p, prev_cpu, wake_flags, &found);
cpu = scx_select_cpu_dfl(p, prev_cpu, wake_flags, 0, &found);
p->scx.selected_cpu = cpu;
if (found) {
p->scx.slice = SCX_SLICE_DFL;

41
kernel/sched/ext_idle.c
View file

@ -418,7 +418,7 @@ void scx_idle_update_selcpu_topology(struct sched_ext_ops *ops)
* NOTE: tasks that can only run on 1 CPU are excluded by this logic, because
* we never call ops.select_cpu() for them, see select_task_rq().
*/
s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags, bool *found)
s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags, u64 flags, bool *found)
{
const struct cpumask *llc_cpus = NULL;
const struct cpumask *numa_cpus = NULL;
@ -455,12 +455,13 @@ s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags, bool
* If WAKE_SYNC, try to migrate the wakee to the waker's CPU.
*/
if (wake_flags & SCX_WAKE_SYNC) {
cpu = smp_processor_id();
int waker_node;
/*
* If the waker's CPU is cache affine and prev_cpu is idle,
* then avoid a migration.
*/
cpu = smp_processor_id();
if (cpus_share_cache(cpu, prev_cpu) &&
scx_idle_test_and_clear_cpu(prev_cpu)) {
cpu = prev_cpu;
@ -480,9 +481,11 @@ s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags, bool
* piled up on it even if there is an idle core elsewhere on
* the system.
*/
waker_node = cpu_to_node(cpu);
if (!(current->flags & PF_EXITING) &&
cpu_rq(cpu)->scx.local_dsq.nr == 0 &&
!cpumask_empty(idle_cpumask(cpu_to_node(cpu))->cpu)) {
(!(flags & SCX_PICK_IDLE_IN_NODE) || (waker_node == node)) &&
!cpumask_empty(idle_cpumask(waker_node)->cpu)) {
if (cpumask_test_cpu(cpu, p->cpus_ptr))
goto cpu_found;
}
@ -521,15 +524,25 @@ s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags, bool
}
/*
* Search for any full idle core usable by the task.
* Search for any full-idle core usable by the task.
*
* If NUMA aware idle selection is enabled, the search will
* If the node-aware idle CPU selection policy is enabled
* (%SCX_OPS_BUILTIN_IDLE_PER_NODE), the search will always
* begin in prev_cpu's node and proceed to other nodes in
* order of increasing distance.
*/
cpu = scx_pick_idle_cpu(p->cpus_ptr, node, SCX_PICK_IDLE_CORE);
cpu = scx_pick_idle_cpu(p->cpus_ptr, node, flags | SCX_PICK_IDLE_CORE);
if (cpu >= 0)
goto cpu_found;
/*
* Give up if we're strictly looking for a full-idle SMT
* core.
*/
if (flags & SCX_PICK_IDLE_CORE) {
cpu = prev_cpu;
goto out_unlock;
}
}
/*
@ -560,18 +573,24 @@ s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags, bool
/*
* Search for any idle CPU usable by the task.
*
* If the node-aware idle CPU selection policy is enabled
* (%SCX_OPS_BUILTIN_IDLE_PER_NODE), the search will always begin
* in prev_cpu's node and proceed to other nodes in order of
* increasing distance.
*/
cpu = scx_pick_idle_cpu(p->cpus_ptr, node, 0);
cpu = scx_pick_idle_cpu(p->cpus_ptr, node, flags);
if (cpu >= 0)
goto cpu_found;
rcu_read_unlock();
return prev_cpu;
cpu = prev_cpu;
goto out_unlock;
cpu_found:
*found = true;
out_unlock:
rcu_read_unlock();
*found = true;
return cpu;
}
@ -810,7 +829,7 @@ __bpf_kfunc s32 scx_bpf_select_cpu_dfl(struct task_struct *p, s32 prev_cpu,
goto prev_cpu;
#ifdef CONFIG_SMP
return scx_select_cpu_dfl(p, prev_cpu, wake_flags, is_idle);
return scx_select_cpu_dfl(p, prev_cpu, wake_flags, 0, is_idle);
#endif
prev_cpu:

2
kernel/sched/ext_idle.h
View file

@ -27,7 +27,7 @@ static inline s32 scx_pick_idle_cpu(const struct cpumask *cpus_allowed, int node
}
#endif /* CONFIG_SMP */
s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags, bool *found);
s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags, u64 flags, bool *found);
void scx_idle_enable(struct sched_ext_ops *ops);
void scx_idle_disable(void);
int scx_idle_init(void);