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…
--
Oleksandr Natalenko (post-factum)
