linux-kernel - Re: [PATCH -next 00/11] support concurrent sync io for bfq on a specail occasion

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Message-ID: <20220413111216.npgrdzaubsvjsmy3@quack3.lan>
Date:   Wed, 13 Apr 2022 13:12:16 +0200
From:   Jan Kara <jack@...e.cz>
To:     Yu Kuai <yukuai3@...wei.com>
Cc:     tj@...nel.org, axboe@...nel.dk, paolo.valente@...aro.org,
        jack@...e.cz, cgroups@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com
Subject: Re: [PATCH -next 00/11] support concurrent sync io for bfq on a
 specail occasion

On Sat 05-03-22 17:11:54, Yu Kuai wrote:
> Currently, bfq can't handle sync io concurrently as long as they
> are not issued from root group. This is because
> 'bfqd->num_groups_with_pending_reqs > 0' is always true in
> bfq_asymmetric_scenario().
> 
> This patchset tries to support concurrent sync io if all the sync ios
> are issued from the same cgroup:
> 
> 1) Count root_group into 'num_groups_with_pending_reqs', patch 1-5;

Seeing the complications and special casing for root_group I wonder: Won't
we be better off to create fake bfq_sched_data in bfq_data and point
root_group->sched_data there? AFAICS it would simplify the code
considerably as root_group would be just another bfq_group, no need to
special case it in various places, no games with bfqg->my_entity, etc.
Paolo, do you see any problem with that?

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR