From: Paolo Valente <paolo.valente@linaro.org>
To: bfq-iosched@googlegroups.com
Cc: Tejun Heo <tj@kernel.org>,
Angelo Ruocco <angelo.ruocco.90@gmail.com>,
Jens Axboe <axboe@kernel.dk>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Li Zefan <lizefan@huawei.com>,
Angelo Ruocco <angeloruocco90@gmail.com>,
Dennis Zhou <dennis@kernel.org>,
Josef Bacik <josef@toxicpanda.com>,
Liu Bo <bo.liu@linux.alibaba.com>,
Bart Van Assche <bvanassche@acm.org>,
Johannes Weiner <hannes@cmpxchg.org>,
linux-block <linux-block@vger.kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Ulf Hansson <ulf.hansson@linaro.org>,
Linus Walleij <linus.walleij@linaro.org>,
broonie@kernel.org, oleksandr@natalenko.name,
cgroups@vger.kernel.org, linux-doc@vger.kernel.org,
Jonathan Corbet <corbet@lwn.net>
Subject: Re: [PATCH V2 00/10] unify the interface of the proportional-share policy in blkio/io
Date: Tue, 18 Dec 2018 19:05:42 +0100 [thread overview]
Message-ID: <E6C76EEB-122B-4FE5-A670-FA066F813C1D@linaro.org> (raw)
In-Reply-To: <EC4F9B54-2352-4D85-B56C-5800CFEBCCB8@linaro.org>
> Il giorno 18 dic 2018, alle ore 18:22, Paolo Valente <paolo.valente@linaro.org> ha scritto:
>
>
>
>> Il giorno 18 dic 2018, alle ore 17:41, Tejun Heo <tj@kernel.org> ha scritto:
>>
>> Hello, Paolo.
>>
>> On Tue, Dec 18, 2018 at 08:48:10AM +0100, Paolo Valente wrote:
>>> If Tejun cannot see any solution to his concern, then can we just
>>> switch to this extension, considering that
>>> - for non-shared names the interface is *identical* to the current
>>> one;
>>> - by using this new interface, and getting feedback we could
>>> understand how to better handle Tejun's concern?
>>> A lot of systems do use weights, and people don't even know that these
>>> systems don't work correctly in blk-mq. And they won't work correctly
>>> in any available configuration from 4.21, if we don't fix this problem.
>>
>> So, when seen from userland, how it should behave isn't vague or
>> complicated. For a given device and policy type, there can be only
>> one implementation active.
>
> Yes, but the problem is the opposite. You may have
> - two different policies, with the same interface parameter,
> - one active on one device
> - the other one active on another device
>
> In that case, statistics from one policy necessarily differ from
> statistics from the other policy.
>
> In this respect, in a system with more than one drive it already
> happens that the same policy is active on different devices. When
> printing a statistics interface file for the policy, the output will
> be a list of separate statistics, with a bunch of statistics *for
> each* drive (plus a grand total in some cases).
>
> So, our proposal simply extends this scheme in the most natural way:
> if, now, also two or more policies share the same statistics file,
> then the output will be a list of separate statistics, one for each
> policy. The statistics for each policy will be tagged with the policy
> name, and will have the same identical form as above. It seems the
> most natural hierarchical extension of the same scheme.
>
> At any rate, if you don't like it, just tell us how you prefer it
> done. Do you prefer the sharing of statistics file to be simply
> forbidden? (If this can be done.) I think such an incomplete solution
> would preserve part of the current mess; but, if this allows us to
> exit from this impasse, then it is ok for me.
>
> *Any* feasible option is ok for me. Just pick one.
>
>> It doesn't make sense to have two weight
>> mechanisms active on one device, right?
>
> (Un)fortunately, the problem are not weights. There won't be two
> weights for two policies expiring a weight parameter. The problems
s/expiring/sharing sorry
next prev parent reply other threads:[~2018-12-18 18:05 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-19 10:34 [PATCH V2 00/10] unify the interface of the proportional-share policy in blkio/io Paolo Valente
2018-11-19 10:34 ` [PATCH V2 01/10] cgroup: add hook seq_show_cft with also the owning cftype as parameter Paolo Valente
2018-11-19 10:34 ` [PATCH V2 02/10] block, cgroup: pass cftype to functions that need to use it Paolo Valente
2018-11-19 10:34 ` [PATCH V2 03/10] cgroup: link cftypes of the same subsystem with the same name Paolo Valente
2018-11-19 10:34 ` [PATCH V2 04/10] cgroup: add owner name to cftypes Paolo Valente
2018-11-19 10:34 ` [PATCH V2 05/10] block, bfq: align min and default weights with the old cfq default Paolo Valente
2018-11-19 10:34 ` [PATCH V2 06/10] cgroup: make all functions of all cftypes be invoked Paolo Valente
2018-11-19 10:34 ` [PATCH V2 07/10] block, bfq: use standard file names for the proportional-share policy Paolo Valente
2018-11-19 10:34 ` [PATCH V2 08/10] block, throttle: allow sharing cgroup statistic files Paolo Valente
2018-11-19 10:34 ` [PATCH V2 09/10] doc, bfq-iosched: fix a few clerical errors Paolo Valente
2018-11-19 10:34 ` [PATCH V2 10/10] doc, bfq-iosched: make it consistent with the new cgroup interface Paolo Valente
2018-11-20 16:28 ` [PATCH V2 00/10] unify the interface of the proportional-share policy in blkio/io Tejun Heo
2018-11-20 16:50 ` Paolo Valente
2018-11-30 18:23 ` Paolo Valente
2018-11-30 18:42 ` Tejun Heo
2018-11-30 18:53 ` Paolo Valente
2018-12-10 13:45 ` Angelo Ruocco
2018-12-18 7:48 ` Paolo Valente
2018-12-18 16:41 ` Tejun Heo
2018-12-18 17:22 ` Paolo Valente
2018-12-18 18:05 ` Paolo Valente [this message]
2018-12-23 11:00 ` Paolo Valente
2018-12-27 23:41 ` Tejun Heo
2018-12-30 10:25 ` Paolo Valente
2019-01-02 16:03 ` Tejun Heo
2019-01-02 16:28 ` Paolo Valente
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