Re: [PATCH RFC 0/9] support concurrent sync io for bfq on a specail occasion

[yukuai (C)]

在 2021/12/10 17:20, Paolo Valente 写道:
> > Il giorno 27 nov 2021, alle ore 11:11, Yu Kuai <yukuai3@xxxxxxxxxx> 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@xxxxxxxxxx/t/
> >
> > 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.
> > 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. So
that sync io on c2 can be handled concurrently.

Thanks,
Kuai

> Thanks,
> Paolo
>
> > 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
>
> .