[PATCH 27/27] kthread: Comment on the purpose and placement of kthread_affine_node() call

[Frederic Weisbecker]

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@xxxxxxxxxxxxx>
Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
---
 kernel/kthread.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 8c1268c2cee9..85e29b250107 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -454,6 +454,10 @@ 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();
 
-- 
2.48.1