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

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Message-ID: <f7900f33-5f27-a6e3-ee3d-f68ad9d8a6d3@huawei.com>
Date:   Tue, 7 Sep 2021 19:19:20 +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 2/4] block, bfq: do not idle if only one cgroup is
 activated

On 2021/09/07 17:10, Paolo Valente wrote:
> 
> 
>> Il giorno 2 set 2021, alle ore 15:31, yukuai (C) <yukuai3@...wei.com> ha scritto:
>>
>> 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
> 
> Unfortunately, if active queues have different weights or belong to
> different classes, then idling is needed to preserve per-queue
> bandwidths.
> 
> Thanks,
> Paolo

Hi, Paolo

It's right, if num_groups_with_pending_reqs == 1, multiple_classes_busy
should be checked, while smallest_weight and varied_queue_weights can
be skipped.

Thanks
Kuai

> .
>