Re: [PATCH 1/3] block, bfq: do not idle if only one cgroup is activated

From: yukuai (C)
Date: Sun Jul 25 2021 - 21:16:15 EST

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

Il giorno 14 lug 2021, alle ore 11:45, Yu Kuai <yukuai3@xxxxxxxxxx> 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

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

Best regards,