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From: Paolo Valente <>
To: "yukuai (C)" <>
Cc: Jens Axboe <>,,,
Subject: Re: [PATCH 1/3] block, bfq: do not idle if only one cgroup is activated
Date: Tue, 3 Aug 2021 09:07:54 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

> Il giorno 31 lug 2021, alle ore 09:10, yukuai (C) <> ha scritto:
> On 2021/07/24 15:12, Paolo Valente wrote:
>>> Il giorno 14 lug 2021, alle ore 11:45, Yu Kuai <> 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, Paolo


> I'm trying to add support to judge if root group have pending rqs, the
> implementation involve setting and clearing the busy state.

I wouldn't use the busy state, as it does not take in-flight requests
into account.  For I/O control, the latter are as important as the
ones still queued in the scheduler.  For this reason, I take in-flight
requests into account when counting

See, e.g., this

	if (!bfqq->dispatched && !bfq_bfqq_busy(bfqq)) {
		bfq_weights_tree_remove(bfqd, bfqq);

in bfq_completed_request.

I would replicate the same logic in deciding whether the root group
has pending I/O.

> I'm thinking about setting busy in __bfq_activate_entity() if
> bfq_entity_to_bfqq() return valid bfqq, however I'm not sure where to
> clear the busy state.
> On the other hand, do you think the way I record rq size info in patch 2
> is OK?

First, let's see what you reply to my suggestion above.


>  If so, I can do this the similar way: say that root group doesn't
> have any pending requests if bfq haven't dispatch rq from root group for
> a period of time.
> Thanks
> Kuai

  reply	other threads:[~2021-08-03  7:08 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-14  9:45 [PATCH 0/3] optimize the queue idle judgment Yu Kuai
2021-07-14  9:45 ` [PATCH 1/3] block, bfq: do not idle if only one cgroup is activated Yu Kuai
2021-07-24  7:12   ` Paolo Valente
2021-07-26  1:15     ` yukuai (C)
2021-07-31  7:10     ` yukuai (C)
2021-08-03  7:07       ` Paolo Valente [this message]
2021-08-03 11:30         ` yukuai (C)
2021-07-14  9:45 ` [PATCH 2/3] block, bfq: add support to record request size information Yu Kuai
2021-07-14  9:45 ` [PATCH 3/3] block, bfq: consider request size in bfq_asymmetric_scenario() Yu Kuai
2021-07-20 12:33 ` [PATCH 0/3] optimize the queue idle judgment yukuai (C)

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