Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Content-Type: text/plain;
        charset=us-ascii
Mime-Version: 1.0 (Mac OS X Mail 12.2 \(3445.102.3\))
Subject: Re: [PATCH 1/1] block, bfq: delete "bfq" prefix from cgroup filenames
From:   Paolo Valente <paolo.valente@linaro.org>
In-Reply-To: <85f1978b-bb31-c6bc-e824-c0682bbd2922@kernel.dk>
Date:   Mon, 8 Apr 2019 17:15:23 +0200
Cc:     Johannes Thumshirn <jthumshirn@suse.de>,
        linux-block <linux-block@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Mark Brown <broonie@kernel.org>,
        'Paolo Valente' via bfq-iosched 
        <bfq-iosched@googlegroups.com>,
        Oleksandr Natalenko <oleksandr@natalenko.name>,
        Angelo Ruocco <angeloruocco90@gmail.com>,
        lennart@poettering.net, mkoutny@suse.cz
Content-Transfer-Encoding: quoted-printable
Message-Id: <4796D9F5-C30F-442D-B3A2-AF80F6874C2C@linaro.org>
References: <20190408143935.9062-1-paolo.valente@linaro.org>
 <20190408143935.9062-2-paolo.valente@linaro.org>
 <20190408144925.GA23021@linux-x5ow.site>
 <7B68DAA9-61D9-4AE0-9FA9-05C07C7FE408@linaro.org>
 <20190408150430.GB23021@linux-x5ow.site>
 <df1dfe5d-c763-91c2-4aca-25d4622c4820@kernel.dk>
 <938957C8-3A0F-4664-8D1F-A822F6D6D4E7@linaro.org>
 <85f1978b-bb31-c6bc-e824-c0682bbd2922@kernel.dk>
To:     Jens Axboe <axboe@kernel.dk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> Il giorno 8 apr 2019, alle ore 17:11, Jens Axboe <axboe@kernel.dk> ha =
scritto:
>=20
> On 4/8/19 9:06 AM, Paolo Valente wrote:
>>=20
>>=20
>>> Il giorno 8 apr 2019, alle ore 17:05, Jens Axboe <axboe@kernel.dk> =
ha scritto:
>>>=20
>>> On 4/8/19 9:04 AM, Johannes Thumshirn wrote:
>>>> [+Cc Michal ]
>>>> On Mon, Apr 08, 2019 at 04:54:39PM +0200, Paolo Valente wrote:
>>>>>=20
>>>>>=20
>>>>>> Il giorno 8 apr 2019, alle ore 16:49, Johannes Thumshirn =
<jthumshirn@suse.de> ha scritto:
>>>>>>=20
>>>>>> On Mon, Apr 08, 2019 at 04:39:35PM +0200, Paolo Valente wrote:
>>>>>>> From: Angelo Ruocco <angeloruocco90@gmail.com>
>>>>>>>=20
>>>>>>> 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].
>>>>>>>=20
>>>>>>> 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.
>>>>>>>=20
>>>>>>> [1] https://github.com/systemd/systemd/issues/7057
>>>>>>=20
>>>>>> Hmm, but isn't this a user-space facing interface and thus some =
sort of ABI?
>>>>>> Do you know what's using it and what breaks due to this =
conversion?
>>>>>>=20
>>>>>=20
>>>>> Yep, but AFAIK, the problem is exactly the opposite: nobody uses =
these
>>>>> names for the proportional-share policy, or wants to use these =
names. I'm
>>>>> CCing Lennart too, in case he has some improbable news on this.
>>>>>=20
>>>>> So the idea is to align names to what people expect, possibly =
before
>>>>> more confusion arises.
>>>>=20
>>>> OK, crazy idea, not sure if Jens and Tejun will beat me for this, =
but
>>>> symlinks?
>>>>=20
>>>> This way we can a) keep the old files and b) have them point to the =
new (a.k.a
>>>> cfq style) files.
>>>=20
>>> I did consider that, and that would be doable. But honestly, I'm =
having a
>>> hard time seeing what issue we are attempting to fix by doing this.
>>>=20
>>=20
>> The problem is ~100% of people and software believing to set weights =
and not doing it.
>=20
> I'm sorry, but I don't know what that means?
>=20

It means that people and code set weights, not bfq.weights.

Thanks,
Paolo

> --=20
> Jens Axboe