> Il giorno 24 ago 2021, alle ore 12:56, Michal Koutný <mkoutny@xxxxxxxx> 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. 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
