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SubjectRe: [PATCH 2/4] block, bfq: avoid moving bfqq to it's parent bfqg
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在 2021/12/21 18:16, Jan Kara 写道:
> On Tue 21-12-21 11:21:33, Yu Kuai wrote:
>> Moving bfqq to it's parent bfqg is pointless.
>>
>> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
>
> 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
>
>> ---
>> 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
>>

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