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Subject: Re: [PATCH 1/1] block, bfq: delete "bfq" prefix from cgroup filenames
From:   Paolo Valente <paolo.valente@linaro.org>
In-Reply-To: <df1dfe5d-c763-91c2-4aca-25d4622c4820@kernel.dk>
Date:   Mon, 8 Apr 2019 17:06:47 +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
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Message-Id: <938957C8-3A0F-4664-8D1F-A822F6D6D4E7@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>
To:     Jens Axboe <axboe@kernel.dk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> 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

The problem is ~100% of people and software believing to set weights and =
not doing it.

Paolo

> --=20
> Jens Axboe