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[66.29.188.166]) by smtp.gmail.com with ESMTPSA id 66sm56181877pfr.44.2019.04.08.08.05.20 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 08 Apr 2019 08:05:21 -0700 (PDT) Subject: Re: [PATCH 1/1] block, bfq: delete "bfq" prefix from cgroup filenames To: Johannes Thumshirn , Paolo Valente Cc: linux-block , linux-kernel , Ulf Hansson , Linus Walleij , Mark Brown , 'Paolo Valente' via bfq-iosched , Oleksandr Natalenko , Angelo Ruocco , lennart@poettering.net, mkoutny@suse.cz 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> From: Jens Axboe Message-ID: Date: Mon, 8 Apr 2019 09:05:19 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190408150430.GB23021@linux-x5ow.site> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org 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 ha scritto: >>> >>> On Mon, Apr 08, 2019 at 04:39:35PM +0200, Paolo Valente wrote: >>>> From: Angelo Ruocco >>>> >>>> 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. -- Jens Axboe