Hi Mete, thanks for taking a look.
On 8/10/26 5:28 PM, Mete Durlu wrote:
Hi,
...
For majority of the cases this would still keep select_fallback_rq
as O(N). task_has_preferred_cpus which is O(N) is called only if
!cpu_preferred. Then task running there is expected to move out.
So subsequent it should run on preferred CPU. This becomes O(N**2)
only for tasks pinned only non preferred CPUs. That is rare case.
Signed-off-by: Shrikanth Hegde <[email protected]>
---
kernel/sched/core.c | 12 ++++++++++--
kernel/sched/sched.h | 12 ++++++++++++
2 files changed, 22 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a45f7c308329..9e8eec4451b6 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2509,8 +2509,12 @@ static inline bool is_cpu_allowed(struct
task_struct *p, int cpu)
return cpu_online(cpu);
/* Non kernel threads are not allowed during either online or
offline. */
- if (!(p->flags & PF_KTHREAD))
+ if (!(p->flags & PF_KTHREAD)) {
+ /* Try to use preferred CPU if task's affinity allows */
+ if (task_can_sched_on_preferred(cpu, p))
+ return false;
return cpu_active(cpu);
+ }
/* KTHREAD_IS_PER_CPU is always allowed. */
if (kthread_is_per_cpu(p))
@@ -2520,7 +2524,11 @@ static inline bool is_cpu_allowed(struct
task_struct *p, int cpu)
if (cpu_dying(cpu))
return false;
- /* But are allowed during online. */
+ /* Try to keep unbound kthreads on a preferred CPU if possible. */
+ if (task_can_sched_on_preferred(cpu, p))
+ return false;
+
+ /* Otherwise, they are allowed to run on online CPU. */
return cpu_online(cpu);
}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 26ae13c86b69..6de6366f2faa 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -4230,4 +4230,16 @@ DEFINE_CLASS_IS_UNCONDITIONAL(sched_change)
#include "ext/ext.h"
+static inline bool task_can_sched_on_preferred(int cpu, struct
task_struct *p)
Sorry, I glanced to the earlier versions but I couldn't find
the answer to my question. Trivial one but still.
FWICT, task_can_sched_on_preferred() is only being used in
core.c, is there a reason why it is defined in
kernel/sched/sched.h and not in core.c ?
Will move it out of sched.h. Thanks for pointing it out.
Thanks.
-Mete
Also, thanks for checking that s390 change.
