Ah yes indeed, I missed this important bit when I last read https://systemd.io/CGROUP_DELEGATION/ :On Thu, Apr 8, 2021 at 6:19 PM Hadrien Grasland <hadrien.grasland@xxxxxxxxxxxxxxx> wrote:
Le 08/04/2021 à 16:11, Lennart Poettering a écrit :
> On Do, 08.04.21 12:24, Hadrien Grasland (hadrien.grasland@xxxxxxxxxxxxxxx) wrote:
>
>> Hi everyone,
>>
>> In a scenario where running benchmarks on dedicated hardware is not
>> possible, I'm trying to momentarily cap the I/O bandwidth used by
>> interactive user sessions while benchmarks are running, in order to improve
>> the stability of said benchmark's I/O performance.
> Is this on cgroupsv1 or cgroupsv2?
>
> IIRC there was some issue that the block io controller wasn't fully
> recursive on cgroupsv1. It should work on cgroupsv2.
This is on a hybrid cgroup configuration. I (perhaps mistakenly) assumed
that modern systemd (v246) will use the cgroups v2 hierarchy in that
case, even though cgroups v1 is still exposed for compatibility with
older apps.
If e.g. the io controller is exposed through cgroups v1, as far as I know it cannot be simultaneously used through cgroups v2, and vice versa.
(Hmm, wasn't there an option to choose which controllers to assign to v1 and which ones to v2?)
"Note that in
[hybrid] mode the unified hierarchy won’t have controllers
attached, the
controllers are all mounted as separate hierarchies as in legacy
mode,
i.e. /sys/fs/cgroup/unified/
is purely and exclusively about core cgroup v2
functionality and not about resource management."
Then I guess unless your parenthesized comment is correct (which means that the above doc is out of date), I must use pure unified/cgroups2 mode in order to do what I want with IO... except I can't switch to it because this will break slurm's cgroups support, which I need for a couple of other things, as it seems Slurm only supports v1 at the moment : https://groups.google.com/g/slurm-users/c/z57-Z3Tz0Oc?pli=1 . Hmmm...
I'd appreciate any confirmation/refuttal on the ability to do adjust controller asignment in a fine-grained way, otherwise it seems I'll need to live without I/O caps until slurm implements cgroup v2 support.
Hadrien
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