linux-kernel - Re: [PATCH v2 4/4] block, bfq: consider request size in bfq_asymmetric

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Date:   Wed, 15 Sep 2021 15:47:54 +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 v2 4/4] block, bfq: consider request size in
 bfq_asymmetric_scenario()

On 2021/09/15 15:36, Paolo Valente wrote:
> 
> 
>> Il giorno 7 set 2021, alle ore 13:29, yukuai (C) <yukuai3@...wei.com> ha scritto:
>>
>> On 2021/08/27 1:00, Paolo Valente wrote:
>>>> Il giorno 6 ago 2021, alle ore 04:08, Yu Kuai <yukuai3@...wei.com> ha scritto:
>>>>
>>>> There is a special case when bfq do not need to idle when more than
>>>> one groups is active:
>>>>
>>> Unfortunately, there is a misunderstanding here.  If more than one
>>> group is active, then idling is not needed only if a lot of symmetry
>>> conditions also hold:
>>> - all active groups have the same weight
>>> - all active groups contain the same number of active queues
>>
>> Hi, Paolo
>>
>> I didn't think of this contition.
>>
>> It's seems that if we want to idle when more than one group is active,
>> there are two additional conditions:
>>
>> - all dispatched requests have the same size
>> - all active groups contain the same number of active queues
>>
> 
> Also the weights and the I/O priorities of the queues inside the
> groups needs to be controlled, unfortunately.
> 
>> Thus we still need to track how many queues are active in each group.
>> The conditions seems to be too much, do you think is it worth it to
>> add support to idle when more than one group is active?
>>
> 
> I think I see your point.  The problem is that these states are
> dynamic.  So, if we suspend tracking all the above information while
> more than one group is active, then we are with no state in case only
> one group remains active.

Hi, Paolo

In this case, I'll drop the last two patches in the next iteration.

Thanks,
Kuai