[PATCH 29/33] kthread: Comment on the purpose and placement of kthread_affine_node() call

Frederic Weisbecker
2025-10-13T20:35:45Z

It may not appear obvious why kthread_affine_node() is not called before
the kthread creation completion instead of after the first wake-up.

The reason is that kthread_affine_node() applies a default affinity
behaviour that only takes place if no affinity preference have already
been passed by the kthread creation call site.

Add a comment to clarify that.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
kernel/kthread.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 4d3cc04e5e8b..d36bdfbd004e 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -453,6 +453,10 @@ static int kthread(void *_create)

self->started = 1;

+ /*
+ * Apply default node affinity if no call to kthread_bind[_mask]() nor
+ * kthread_affine_preferred() was issued before the first wake-up.
+ */
if (!(current->flags & PF_NO_SETAFFINITY) && !self->preferred_affinity)
kthread_affine_node();

--
2.51.0