Il giorno 31 lug 2021, alle ore 09:10, yukuai (C) [off-list ref] ha scritto:

On 2021/07/24 15:12, Paolo Valente wrote:

quoted

quoted

Il giorno 14 lug 2021, alle ore 11:45, Yu Kuai [off-list ref] 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

Hi

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
bfqd->num_groups_with_pending_reqs.

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.

Thanks,
Paolo

 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