linux-kernel - Re: [PATCH v4 1/2] block, bfq: counted root group into 'num_groups_with_pending

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Message-ID: <c61ea2d2-91e7-249b-ac1c-e6e2240f88ae@huawei.com>
Date:   Wed, 20 Oct 2021 19:53:49 +0800
From:   "yukuai (C)" <yukuai3@...wei.com>
To:     Paolo Valente <paolo.valente@...aro.org>
CC:     Jens Axboe <axboe@...nel.dk>,
        linux-block <linux-block@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <yi.zhang@...wei.com>
Subject: Re: [PATCH v4 1/2] block, bfq: counted root group into
 'num_groups_with_pending_reqs'

On 2021/10/20 17:43, Paolo Valente wrote:
> 
> 
>> Il giorno 20 ott 2021, alle ore 11:38, yukuai (C) <yukuai3@...wei.com> ha scritto:
>>
>> On 2021/10/20 17:29, Paolo Valente wrote:
>>>> Il giorno 20 ott 2021, alle ore 11:20, yukuai (C) <yukuai3@...wei.com> ha scritto:
>>>>
>>>> On 2021/10/20 16:51, Paolo Valente wrote:
>>>>
>>>>>> @@ -860,9 +870,25 @@ void bfq_weights_tree_remove(struct bfq_data *bfqd,
>>>>>> 			     struct bfq_queue *bfqq)
>>>>>> {
>>>>>> 	struct bfq_entity *entity = bfqq->entity.parent;
>>>>>> +	struct bfq_sched_data *sd;
>>>>>> +
>>>>>> +	/*
>>>>>> +	 * If the bfq queue is in root group, the decrement of
>>>>>> +	 * num_groups_with_pending_reqs is performed immediately upon the
>>>>>> +	 * deactivation of entity.
>>>>>> +	 */
>>>>>> +	if (!entity) {
>>>>>> +		entity = &bfqd->root_group->entity;
>>>>>> +		sd = entity->my_sched_data;
>>>>>> +
>>>>>> +		if (!sd->in_service_entity)
>>>>>> +			bfq_clear_group_with_pending_reqs(bfqd, entity);
>>>>>> +
>>>>>> +		return;
>>>>>> +	}
>>>>>>
>>>>>> 	for_each_entity(entity) {
>>>>>> -		struct bfq_sched_data *sd = entity->my_sched_data;
>>>>>> +		sd = entity->my_sched_data;
>>>>>>
>>>>>> 		if (sd->next_in_service || sd->in_service_entity) {
>>>>>> 			/*
>>>>>> @@ -880,7 +906,8 @@ void bfq_weights_tree_remove(struct bfq_data *bfqd,
>>>>>> 		}
>>>>>>
>>>>>> 		/*
>>>>>> -		 * The decrement of num_groups_with_pending_reqs is
>>>>>> +		 * If the bfq queue is not in root group,
>>>>>> +		 * the decrement of num_groups_with_pending_reqs is
>>>>> I'm sorry if I didn't notice this before, but why do you postpone the
>>>>> decrement only for queues not in root group?  If I'm not missing
>>>>> anything, the active (i.e., with pending reqs) state of the root group
>>>>> is to be computed as that of ay other group.
>>>>
>>>> Hi, Paolo
>>>>
>>>> I thought if queue is in root group, then bfqq->entity.parent is NULL,
>>>> and such case is handled above, which is separate from previous
>>>> implementation for queues that are not in root group.
>>>>
>>>> Is this the wrong way to handle root group?
>>>>
>>> I think that, if we want to count also the root group among the active
>>> ones, then the logic for tagging the root group as active must be the
>>> same as the other groups. Or am I missing something?
>>
>> Hi, Paolo
>>
>> Currently, if queue is in root group, bfqq->entity.parent is NULL, and
>> this makes it hard to keep the same logic.
>>
>> Can we store root_group->my_entity to bfqq->entity.parent if the queue
>> is in root group?
>>
> 
> Any sensible implementation is ok for me.  Usually, stuff for root
> group is in the bfqd.
> 

I'll try to do implement that way,

Thanks,
Kuai

> Thanks,
> Paolo
> 
>> Thanks,
>> Kuai
> 
> .
>