Re: [PATCH block/for-5.2-fixes] bfq: use io.weight interface file instead of io.bfq.weight

From: Paolo Valente <paolo.valente@linaro.org>
To: Tejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Jens Axboe <axboe@kernel.dk>, Li Zefan <lizefan@huawei.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	Johannes Thumshirn <jthumshirn@suse.de>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	Fam Zheng <fam@euphon.net>
Subject: Re: [PATCH block/for-5.2-fixes] bfq: use io.weight interface file instead of io.bfq.weight
Date: Wed, 12 Jun 2019 09:32:07 +0200	[thread overview]
Message-ID: <A1C3E3D8-62E3-4BD3-86B4-59E7E1319EA8@linaro.org> (raw)
In-Reply-To: <20190611211718.GM3341036@devbig004.ftw2.facebook.com>

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> Il giorno 11 giu 2019, alle ore 23:17, Tejun Heo <tj@kernel.org> ha scritto:
> 
> On Tue, Jun 11, 2019 at 12:49:59PM -0700, Tejun Heo wrote:
>> (Description mostly stolen from 19e9da9e86c4 ("block, bfq: add weight
>> symlink to the bfq.weight cgroup parameter")
>> 
>> Many userspace tools and services use the proportional-share policy of
>> the blkio/io cgroups controller. The CFQ I/O scheduler implemented
>> this policy for the legacy block layer. To modify the weight of a
>> group in case CFQ was in charge, the 'weight' parameter of the group
>> must be modified. On the other hand, the BFQ I/O scheduler implements
>> the same policy in blk-mq, but, with BFQ, the parameter to modify has
>> a different name: bfq.weight (forced choice until legacy block was
>> present, because two different policies cannot share a common
>> parameter in cgroups).
> 
> Sorry, please don't apply this patch.  The cgroup interface currently
> implemented by bfq doesn't follow the io.weight interface spec.

Could you elaborate a little more on this?

bfq code for setting up and handling io.weight (more precisely
io.bfq.weight) is a copy and paste of cfq code.

Thanks,
Paolo

> It's
> different from cfq interface and symlinking to or renaming it won't do
> anybody any good.
> 
> For now, the only thing we can do looks like keeping it as-is.
> 
> Thanks.
> 
> --
> tejun

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