Re: [PATCH 1/1] block, bfq: delete "bfq" prefix from cgroup filenames

[Paolo Valente <paolo.valente@linaro.org>]

> Il giorno 8 apr 2019, alle ore 17:11, Jens Axboe <axboe@kernel.dk> ha scritto:
> 
> On 4/8/19 9:06 AM, Paolo Valente wrote:
>> 
>> 
>>> Il giorno 8 apr 2019, alle ore 17:05, Jens Axboe <axboe@kernel.dk> ha scritto:
>>> 
>>> 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:
>>>>> 
>>>>> 
>>>>>> Il giorno 8 apr 2019, alle ore 16:49, Johannes Thumshirn <jthumshirn@suse.de> ha scritto:
>>>>>> 
>>>>>> On Mon, Apr 08, 2019 at 04:39:35PM +0200, Paolo Valente wrote:
>>>>>>> From: Angelo Ruocco <angeloruocco90@gmail.com>
>>>>>>> 
>>>>>>> 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.
>>>>>>> 
>>>>>>> [1] https://github.com/systemd/systemd/issues/7057
>>>>>> 
>>>>>> 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?
>>>>>> 
>>>>> 
>>>>> 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.
>>>>> 
>>>>> So the idea is to align names to what people expect, possibly before
>>>>> more confusion arises.
>>>> 
>>>> OK, crazy idea, not sure if Jens and Tejun will beat me for this, but
>>>> symlinks?
>>>> 
>>>> This way we can a) keep the old files and b) have them point to the new (a.k.a
>>>> cfq style) files.
>>> 
>>> 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.
>>> 
>> 
>> The problem is ~100% of people and software believing to set weights and not doing it.
> 
> I'm sorry, but I don't know what that means?
> 

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

Thanks,
Paolo

> -- 
> Jens Axboe