> Il giorno 12 nov 2018, alle ore 11:00, Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx> ha scritto: > > On 12.11.2018 10:56, Paolo Valente wrote: >> Hi Jens, Tejun, all, >> about nine months ago, we agreed on a solution for unifying the >> interface of the proportional-share policy in blkio/io [1]. Angelo >> and I finally completed it. Let me briefly recall the problem and the >> solution. >> The current implementation of cgroups doesn't allow two or more >> entities, e.g., I/O schedulers, to share the same files. So, if CFQ >> creates its files for the proportional-share policy, such as, e.g, >> weight files for blkio/io groups, BFQ cannot attach somehow to them. >> Thus, to enable people to set group weights with BFQ, I resorted to >> making BFQ create its own version of these common files, by prepending >> a bfq prefix. >> Actually, no legacy code uses these different names, or is likely to >> do so. Having these two sets of names is simply a source of >> confusion, as pointed out also, e.g., by Lennart Poettering (CCed >> here), and acknowledged by Tejun [2]. >> In [1] we agreed on a solution that solves this problem, by actually >> making it possible to share cgroups files. Both writing to and >> reading from a shared file trigger the appropriate operation for each >> of the entities that share the file. In particular, in case of >> reading, >> - if all entities produce the same output, the this common output is >> shown only once; >> - if the outputs differ, then every per-entity output is shown, >> preceded by the name of the entity that produced that output. >> With this solution, legacy code that, e.g., sets group weights, just >> works, regardless of the I/O scheduler actually implementing >> proportional share. >> But note that this extension is not restricted to only blkio/io. The >> general group interface now enables files to be shared among multiple >> entities of any kind. >> (I have also added a patch to fix some clerical errors in bfq doc, >> which I found while making the latter consistent with the new >> interface.) >> Thanks, >> Paolo >> [1] https://lkml.org/lkml/2018/1/4/667 >> [2] https://github.com/systemd/systemd/issues/7057 >> Angelo Ruocco (7): >> kernfs: add function to find kernfs_node without increasing ref >> counter >> cgroup: link cftypes of the same subsystem with the same name >> cgroup: add owner name to cftypes >> block, bfq: align min and default weights with cfq >> cgroup: make all functions of all cftypes be invoked >> block, cfq: allow cgroup files to be shared >> block, throttle: allow sharing cgroup statistic files >> Paolo Valente (5): >> cgroup: add hook seq_show_cft with also the owning cftype as parameter >> block, cgroup: pass cftype to functions that need to use it >> block, bfq: use standard file names for the proportional-share policy >> doc, bfq-iosched: fix a few clerical errors >> doc, bfq-iosched: make it consistent with the new cgroup interface >> Documentation/block/bfq-iosched.txt | 31 +++-- >> block/bfq-cgroup.c | 148 +++++++++++++------- >> block/bfq-iosched.h | 4 +- >> block/blk-cgroup.c | 22 +-- >> block/blk-throttle.c | 24 ++-- >> block/cfq-iosched.c | 105 +++++++++++---- >> fs/kernfs/dir.c | 13 ++ >> include/linux/blk-cgroup.h | 10 +- >> include/linux/cgroup-defs.h | 14 +- >> include/linux/cgroup.h | 13 ++ >> include/linux/kernfs.h | 7 + >> kernel/cgroup/cgroup.c | 262 +++++++++++++++++++++++++++++------- >> 12 files changed, 483 insertions(+), 170 deletions(-) >> -- >> 2.16.1 > > I thought all the legacy stuff including CFS et al. is going to be removed in v4.21 completely… > Thanks for pointing this out. People with a lower kernel version than the future 4.21 just cannot and will not be able to use the proportional share policy on blk-mq (with legacy code), because of the name issue highlighted in this email. If this patch series gets accepted, a backport will solve the problem. In this respect, such a backport might even happen 'automatically', as most bfq commit seem to get backported to older, stable kernels. In addition, this extension - extends the whole cgroups interface, in a seamless and backward-compatible way, to prevent future issues like these; - solves a similar issue with throttle (which AFAIK won't go away with 4.21). Thanks, Paolo > -- > Oleksandr Natalenko (post-factum)
