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

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Message-Id: <38971C09-E691-4129-BE6A-E21337EAE884@linaro.org>
Date:   Fri, 7 Jun 2019 08:20:21 +0200
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-block <linux-block@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        noreply-spamdigest via bfq-iosched 
        <bfq-iosched@...glegroups.com>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Angelo Ruocco <angeloruocco90@...il.com>,
        Fam Zheng <fam@...hon.net>
Subject: Re: [PATCH 0/2] block, bfq: add weight symlink to the bfq.weight
 cgroup parameter

ping

> Il giorno 30 mag 2019, alle ore 17:02, Paolo Valente <paolo.valente@...aro.org> ha scritto:
> 
> Hi Jens,
> have you had time to look into this?
> 
> Thanks,
> Paolo
> 
>> Il giorno 21 mag 2019, alle ore 10:01, Paolo Valente <paolo.valente@...aro.org> ha scritto:
>> 
>> 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.
>> 
>> Thanks,
>> Paolo
>> 
>> [1] https://lkml.org/lkml/2019/4/8/555
>> 
>> Angelo Ruocco (2):
>> cgroup: let a symlink too be created with a cftype file
>> block, bfq: add weight symlink to the bfq.weight cgroup parameter
>> 
>> block/bfq-cgroup.c          |  6 ++++--
>> include/linux/cgroup-defs.h |  3 +++
>> kernel/cgroup/cgroup.c      | 33 +++++++++++++++++++++++++++++----
>> 3 files changed, 36 insertions(+), 6 deletions(-)
>> 
>> --
>> 2.20.1
> 


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