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Date:   Mon, 26 Jul 2021 09:15:54 +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 1/3] block, bfq: do not idle if only one cgroup is
 activated

On 2021/07/24 15:12, Paolo Valente wrote:
> 
> 
>> Il giorno 14 lug 2021, alle ore 11:45, Yu Kuai <yukuai3@...wei.com> ha scritto:
>>
>> If only one group is activated, specifically
>> 'bfqd->num_groups_with_pending_reqs == 1', there is no need to guarantee
>> the same share of the throughput of queues in the same group.
>>
>> Thus change the condition from '> 0' to '> 1' in
>> bfq_asymmetric_scenario().
> 
> I see your point, and I agree with your goal.  Yet, your change seems
> not to suffer from the following problem.
> 
> In addition to the groups that are created explicitly, there is the
> implicit root group.  So, when bfqd->num_groups_with_pending_reqs ==
> 1, there may be both active processes in the root group and active
> processes in the only group created explicitly.  In this case, idling
> is needed to preserve service guarantees.
> 
> Probably your idea should be improved by making sure that there is
> pending I/O only from either the root group or the explicit group.
> 
> Thanks,
> Paolo
> 

Hi,

Thanks for you advice, will do this in the next iteration.

Best regards,
Kuai

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