linux-kernel - Re: [PATCH 0/2] block, bfq: add weight symlink to the bfq.weight cgroup parameter

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Message-ID: <854dd83a-bd07-c1c3-d005-ef7a62f0fa35@kernel.dk>
Date:   Fri, 7 Jun 2019 01:30:10 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Paolo Valente <paolo.valente@...aro.org>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        ulf.hansson@...aro.org, linus.walleij@...aro.org,
        broonie@...nel.org, bfq-iosched@...glegroups.com,
        oleksandr@...alenko.name
Subject: Re: [PATCH 0/2] block, bfq: add weight symlink to the bfq.weight
 cgroup parameter

On 5/21/19 2:01 AM, Paolo Valente wrote:
> 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).
> 
> Due to CFQ legacy, most if not all userspace configurations still use
> the parameter 'weight', and for the moment do not seem likely to be
> changed. But, when CFQ went away with legacy block, such a parameter
> ceased to exist.
> 
> So, a simple workaround has been proposed by Johannes [1] to make all
> configurations work: add a symlink, named weight, to bfq.weight. This
> pair of patches adds:
> 1) the possibility to create a symlink to a cgroup file;
> 2) the above 'weight' symlink.

Applied, thanks.

-- 
Jens Axboe