Forgot to CC Lennart, sorry. > Il giorno 12 nov 2018, alle ore 10:56, Paolo Valente <paolo.valente@xxxxxxxxxx> ha scritto: > > 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
