linux-kernel - Re: [PATCH 2/2] block, bfq: delete "bfq" prefix from cgroup filenames

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Date:   Wed, 18 Sep 2019 08:09:42 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Tejun Heo <tj@...nel.org>, Paolo Valente <paolo.valente@...aro.org>
Cc:     Jens Axboe <axboe@...nel.dk>,
        linux-block <linux-block@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        "'Paolo Valente' via bfq-iosched" <bfq-iosched@...glegroups.com>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        cgroups@...r.kernel.org, Angelo Ruocco <angeloruocco90@...il.com>
Subject: Re: [PATCH 2/2] block, bfq: delete "bfq" prefix from cgroup filenames

Tejun, Paolo,

On Tue, 17 Sep 2019 at 23:32, Tejun Heo <tj@...nel.org> wrote:
>
> Hello,
>
> On Tue, Sep 17, 2019 at 06:51:48PM +0200, Paolo Valente wrote:
> > When bfq was merged into mainline, there were two I/O schedulers that
> > implemented the proportional-share policy: bfq for blk-mq and cfq for
> > legacy blk. bfq's interface files in the blkio/io controller have the
> > same names as cfq. But the cgroups interface doesn't allow two
> > entities to use the same name for their files, so for bfq we had to
> > prepend the "bfq" prefix to each of its files. However no legacy code
> > uses these modified file names. This naming also causes confusion, as,
> > e.g., in [1].
> >
> > Now cfq has gone with legacy blk, so there is no need any longer for
> > these prefixes in (the never used) bfq names. In view of this fact, this
> > commit removes these prefixes, thereby enabling legacy code to truly
> > use the proportional share policy in blk-mq.
>
> So, I wrote the iocost switching patch and don't have a strong
> interest in whether bfq prefix should get dropped or not.  However, I
> gotta point out that flipping interface this way is way out of the
> norm.
>
> In the previous release cycle, the right thing to do was dropping the
> bfq prefix but that wasn't possible because bfq's interface wasn't
> compatible at that point and didn't made to be compatible in time.

Sounds like we really should send those relevant patches for stable,
to set the correct ground. Then using a symlink, to make sure we don't
brake current ABI, right?

[...]

Kind regards
Uffe