ÔÚ 2021/12/21 18:16, Jan Kara дµÀ:

On Tue 21-12-21 11:21:33, Yu Kuai wrote:

quoted

Moving bfqq to it's parent bfqg is pointless.

Signed-off-by: Yu Kuai <redacted>

Did you notice that this is happening often enough that the check is worth
it? Where do we do this?

I noticed that this will happend when root group is offlined:

bfq_pd_offline
  bfq_put_async_queues
   __bfq_put_async_bfqq
    bfq_bfqq_move

I'm not sure if there are other situations. I think bfq_bfqq_move()
is not happening often itself, thus the checking won't affect
performance.

Thanks,
Kuai

								Honza

quoted

---
  block/bfq-cgroup.c | 7 ++++++-
  1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index 24a5c5329bcd..0f62546a72d4 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c

@@ -645,6 +645,11 @@ void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq,
  		   struct bfq_group *bfqg)
  {
  	struct bfq_entity *entity = &bfqq->entity;
+	struct bfq_group *old_parent = bfq_group(bfqq);
+
+	/* No point to move bfqq to the same group */
+	if (old_parent == bfqg)
+		return;
  
  	/*
  	 * Get extra reference to prevent bfqq from being freed in

@@ -666,7 +671,7 @@ void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq,
  		bfq_deactivate_bfqq(bfqd, bfqq, false, false);
  	else if (entity->on_st_or_in_serv)
  		bfq_put_idle_entity(bfq_entity_service_tree(entity), entity);
-	bfqg_and_blkg_put(bfqq_group(bfqq));
+	bfqg_and_blkg_put(old_parent);
  
  	if (entity->parent &&
  	    entity->parent->last_bfqq_created == bfqq)

-- 
2.31.1