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From: Paolo Valente <paolo.valente@linaro.org>
To: "Michal Koutný" <mkoutny@suse.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-block <linux-block@vger.kernel.org>,
	Jan Kara <jack@suse.cz>
Subject: Re: BFQ cgroup weights range
Date: Tue, 24 Aug 2021 14:51:47 +0200	[thread overview]
Message-ID: <EC36D67F-D7CC-4059-8D3B-E0E64DFC3ADB@linaro.org> (raw)
In-Reply-To: <20210824105626.GA11367@blackbody.suse.cz>



> Il giorno 24 ago 2021, alle ore 12:56, Michal Koutný <mkoutny@suse.com> ha scritto:
> 
> Hello.
> 
> The default weight for proportional IO control associated with a cgroup
> is 100 [1]. The minimum allowed weight is 1 [2] and the maximum weight
> 1000 [3].  This is a bit inconsistent with general cgroup weight
> semantic where def/min == max/def (i.e. symmetric adjustments to both
> sides) [4].
> 
> 1) Is there a reason why the maximum allowed weight is (only) 1000?
>   (E.g. it won't be possible to ensure 10^4 ratio of proportional
>   control but 10^3 is achievable.)
> 2) Is the default value 100 special or absolute in a sense? (I suspect
>   it is, the unchangeable weight of root cgroup members. Therefore two
>   siblings with equal ratios 10:100 and 100:1000 would behave same only
>   when there's no interfering IO from the root.)
> 

Hi,
BFQ inherited these constants when we forked it from CFQ.  I'm ok with
increasing max weight to 10000.  I only wonder whether this would
break some configuration, as the currently maximum weight would not be
the maximum weight any longer.
\x14
Thanks,
Paolo

> Thanks,
> Michal
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/block/bfq-cgroup.c?h=v5.14-rc7#n513
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/block/bfq-iosched.h?h=v5.14-rc7#n18
> [3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/block/bfq-iosched.h?h=v5.14-rc7#n19
> [4] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/admin-guide/cgroup-v2.rst?h=v5.14-rc7#n602


  reply	other threads:[~2021-08-24 12:51 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-24 10:56 BFQ cgroup weights range Michal Koutný
2021-08-24 12:51 ` Paolo Valente [this message]
2021-08-26 13:12   ` Michal Koutný
2021-08-26 17:25     ` Tejun Heo
2021-08-27  8:33       ` Paolo Valente

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