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Subject: Re: [PATCH -next v3 2/3] block, bfq: refactor the counting of
 'num_groups_with_pending_reqs'
To:     Jan Kara <jack@suse.cz>
CC:     <tj@kernel.org>, <axboe@kernel.dk>, <paolo.valente@linaro.org>,
        <cgroups@vger.kernel.org>, <linux-block@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <yi.zhang@huawei.com>
References: <20220427124722.48465-1-yukuai3@huawei.com>
 <20220427124722.48465-3-yukuai3@huawei.com>
 <20220427124908.o3cl72h2uflmufso@quack3.lan>
From:   "yukuai (C)" <yukuai3@huawei.com>
Message-ID: <d36b4904-3db8-537c-5040-b496272ccf70@huawei.com>
Date:   Thu, 28 Apr 2022 09:09:36 +0800
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?? 2022/04/27 20:49, Jan Kara д??:
> On Wed 27-04-22 20:47:21, Yu Kuai wrote:
>> Currently, bfq can't handle sync io concurrently as long as they
>> are not issued from root group. This is because
>> 'bfqd->num_groups_with_pending_reqs > 0' is always true in
>> bfq_asymmetric_scenario().
>>
>> The way that bfqg is counted into 'num_groups_with_pending_reqs':
>>
>> Before this patch:
>>   1) root group will never be counted.
>>   2) Count if bfqg or it's child bfqgs have pending requests.
>>   3) Don't count if bfqg and it's child bfqgs complete all the requests.
>>
>> After this patch:
>>   1) root group is counted.
>>   2) Count if bfqg have at least one bfqq that is marked busy.
>>   3) Don't count if bfqg doesn't have any busy bfqqs.
>>
>> With this change, the occasion that only one group is activated can be
>> detected, and next patch will support concurrent sync io in the
>> occasion.
>>
>> This patch also rename 'num_groups_with_pending_reqs' to
>> 'num_groups_with_busy_queues'.
>>
>> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> 
> Looks good. Just I think you forgot to remove in_groups_with_pending_reqs,
> which is now unused, from bfq_entity.

Will remove it in the next iteration.

Thanks,
Kuai