linux-kernel - Re: [PATCH v2 2/4] block, bfq: do not idle if only one cgroup is activated

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Message-ID: <da0e53b4-e947-9c91-832e-36da67037f0f@huawei.com>
Date:   Thu, 2 Sep 2021 21:31:26 +0800
From:   "yukuai (C)" <yukuai3@...wei.com>
To:     Paolo Valente <paolo.valente@...aro.org>
CC:     Jens Axboe <axboe@...nel.dk>, <linux-block@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <yi.zhang@...wei.com>
Subject: Re: [PATCH v2 2/4] block, bfq: do not idle if only one cgroup is
 activated

On 2021/08/27 1:00, Paolo Valente wrote:
> 
> Why do you make these extensive changes, while you can leave all the
> function unchanged and just modify the above condition to something
> like
> 
> || bfqd->num_groups_with_pending_reqs > 1
> || (bfqd->num_groups_with_pending_reqs && bfqd->num_queues_with_pending_reqs_in_root)

Hi, Paolo

I was thinking that if CONFIG_BFQ_GROUP_IOSCHED is enabled, there is no
need to caculate smallest_weight, varied_queue_weights, and
multiple_classes_busy:

If we count root group into num_groups_with_pending_reqs
  - If num_groups_with_pending_reqs <= 1, idle is not needed
  - If num_groups_with_pending_reqs  > 1, idle is needed

Thus such changes can save some additional overhead.

Thanks
Yu Kuai

> 
> In addition, I still wonder whether you can simply add also the root
> group to bfqd->num_groups_with_pending_reqs (when the root group is
> active).  This would make the design much cleaner.
> 
> Thanks,
> Paolo
> 
>> -#endif
>> -		;
>> +	return varied_queue_weights || multiple_classes_busy;
>> }
>>
>> /*
>> -- 
>> 2.31.1
>>
> 
> .
>