Il giorno 10 dic 2021, alle ore 10:50, yukuai (C) [off-list ref] ha scritto:

在 2021/12/10 17:20, Paolo Valente 写道:

quoted

quoted

Il giorno 27 nov 2021, alle ore 11:11, Yu Kuai [off-list ref] ha scritto:

Bfq can't handle sync io concurrently as long as the io are not issued
from root group currently.

Previous patch set:
https://lore.kernel.org/lkml/20211014014556.3597008-2-yukuai3@huawei.com/t/ (local)

During implemting the method mentioned by the above patch set, I found
more problems that will block implemting concurrent sync io. The
modifications of this patch set are as follows:

1) count root group into 'num_groups_with_pending_reqs';
2) don't idle if 'num_groups_with_pending_reqs' is 1;
3) If the group doesn't have pending requests while it's child groups
have pending requests, don't count the group.

Why don't yo count the parent group? It seems to me that we should count it.

Hi, Paolo

For example, we only issue io in child group c2(root->c1->c2),
'num_groups_with_pending_reqs' will end up greater than 1, thus it's
impossible to handle sync io concurrently. Thus I don't count root and
c1, only count c2.

Right!

Please explain this clearly in comments.

quoted

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4) Once the group doesn't have pending requests, decrease
'num_groups_with_pending_reqs' immediately. Don't delay to when all
it's child groups don't have pending requests.

I guess this action is related to 3).

Yes, if c1, c2 are both active, and then c1 don't have any pending reqs,
I want to decrease num_groups_with_pending_reqs to 1 immediately.

I'll check this point directly on the patch that does this decrement,
because something is not clear to me.

Thanks,
Paolo

 So
that sync io on c2 can be handled concurrently.

Thanks,
Kuai

quoted

Thanks,
Paolo

quoted

Noted that I just tested basic functionality of this patchset, and I
think it's better to see if anyone have suggestions or better
solutions.

Yu Kuai (9):
 block, bfq: add new apis to iterate bfq entities
 block, bfq: apply news apis where root group is not expected
 block, bfq: handle the case when for_each_entity() access root group
 block, bfq: count root group into 'num_groups_with_pending_reqs'
 block, bfq: do not idle if only one cgroup is activated
 block, bfq: only count group that the bfq_queue belongs to
 block, bfq: record how many queues have pending requests in bfq_group
 block, bfq: move forward __bfq_weights_tree_remove()
 block, bfq: decrease 'num_groups_with_pending_reqs' earlier

block/bfq-cgroup.c  |  3 +-
block/bfq-iosched.c | 92 +++++++++++++++++++++++----------------------
block/bfq-iosched.h | 41 +++++++++++++-------
block/bfq-wf2q.c    | 44 +++++++++++++++-------
4 files changed, 106 insertions(+), 74 deletions(-)

-- 
2.31.1

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