linux-kernel - Re: [PATCH 00/12] unify the interface of the proportional-share policy in blkio/io

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Date:   Mon, 12 Nov 2018 11:00:55 +0100
From:   Oleksandr Natalenko <oleksandr@...alenko.name>
To:     Paolo Valente <paolo.valente@...aro.org>
Cc:     Jens Axboe <axboe@...nel.dk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
        Angelo Ruocco <angeloruocco90@...il.com>,
        Dennis Zhou <dennis@...nel.org>,
        Josef Bacik <josef@...icpanda.com>,
        Liu Bo <bo.liu@...ux.alibaba.com>,
        Bart Van Assche <bvanassche@....org>,
        Johannes Weiner <hannes@...xchg.org>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        ulf.hansson@...aro.org, linus.walleij@...aro.org,
        broonie@...nel.org, bfq-iosched@...glegroups.com,
        cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
        Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH 00/12] unify the interface of the proportional-share
 policy in blkio/io

On 12.11.2018 10:56, Paolo Valente wrote:
> Hi Jens, Tejun, all,
> about nine months ago, we agreed on a solution for unifying the
> interface of the proportional-share policy in blkio/io [1].  Angelo
> and I finally completed it.  Let me briefly recall the problem and the
> solution.
> 
> The current implementation of cgroups doesn't allow two or more
> entities, e.g., I/O schedulers, to share the same files.  So, if CFQ
> creates its files for the proportional-share policy, such as, e.g,
> weight files for blkio/io groups, BFQ cannot attach somehow to them.
> Thus, to enable people to set group weights with BFQ, I resorted to
> making BFQ create its own version of these common files, by prepending
> a bfq prefix.
> 
> Actually, no legacy code uses these different names, or is likely to
> do so.  Having these two sets of names is simply a source of
> confusion, as pointed out also, e.g., by Lennart Poettering (CCed
> here), and acknowledged by Tejun [2].
> 
> In [1] we agreed on a solution that solves this problem, by actually
> making it possible to share cgroups files.  Both writing to and
> reading from a shared file trigger the appropriate operation for each
> of the entities that share the file.  In particular, in case of
> reading,
> - if all entities produce the same output, the this common output is
>   shown only once;
> - if the outputs differ, then every per-entity output is shown,
>   preceded by the name of the entity that produced that output.
> 
> With this solution, legacy code that, e.g., sets group weights, just
> works, regardless of the I/O scheduler actually implementing
> proportional share.
> 
> But note that this extension is not restricted to only blkio/io.  The
> general group interface now enables files to be shared among multiple
> entities of any kind.
> 
> (I have also added a patch to fix some clerical errors in bfq doc,
> which I found while making the latter consistent with the new
> interface.)
> 
> Thanks,
> Paolo
> 
> [1] https://lkml.org/lkml/2018/1/4/667
> [2] https://github.com/systemd/systemd/issues/7057
> 
> Angelo Ruocco (7):
>   kernfs: add function to find kernfs_node without increasing ref
>     counter
>   cgroup: link cftypes of the same subsystem with the same name
>   cgroup: add owner name to cftypes
>   block, bfq: align min and default weights with cfq
>   cgroup: make all functions of all cftypes be invoked
>   block, cfq: allow cgroup files to be shared
>   block, throttle: allow sharing cgroup statistic files
> 
> Paolo Valente (5):
>   cgroup: add hook seq_show_cft with also the owning cftype as 
> parameter
>   block, cgroup: pass cftype to functions that need to use it
>   block, bfq: use standard file names for the proportional-share policy
>   doc, bfq-iosched: fix a few clerical errors
>   doc, bfq-iosched: make it consistent with the new cgroup interface
> 
>  Documentation/block/bfq-iosched.txt |  31 +++--
>  block/bfq-cgroup.c                  | 148 +++++++++++++-------
>  block/bfq-iosched.h                 |   4 +-
>  block/blk-cgroup.c                  |  22 +--
>  block/blk-throttle.c                |  24 ++--
>  block/cfq-iosched.c                 | 105 +++++++++++----
>  fs/kernfs/dir.c                     |  13 ++
>  include/linux/blk-cgroup.h          |  10 +-
>  include/linux/cgroup-defs.h         |  14 +-
>  include/linux/cgroup.h              |  13 ++
>  include/linux/kernfs.h              |   7 +
>  kernel/cgroup/cgroup.c              | 262 
> +++++++++++++++++++++++++++++-------
>  12 files changed, 483 insertions(+), 170 deletions(-)
> 
> --
> 2.16.1

I thought all the legacy stuff including CFS et al. is going to be 
removed in v4.21 completely…

-- 
   Oleksandr Natalenko (post-factum)