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Support to single cgroup mountpoint? #26

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ghedo opened this Issue · 7 comments

4 participants

Alessandro Ghedini Daniel Poelzleithner Ritesh Raj Sarraf Petr Gajdůšek
Alessandro Ghedini

Hi,

currently ulatencyd uses different mountpoints for cgroupfs (/sys/fs/cgroup/cpu, /sys/fs/cgroup/memory, etc...). What about supporting also a single mountpoint for them all (/sys/fs/cgroup)? Do you think it is doable? What kind of issues this may introduce?

I'm asking because there is a on going discussion in Debian about mounting cgroupfs by default in /sys/fs/cgroup and this would break ulatencyd. This is also valid if someone decides to mount cgroupfs in fstab (see #643580).

Daniel Poelzleithner
Owner

it is possible with configs changes, but not very practical. the problem is, that different cgoup subsystem support different hierarchy levels, blockio for example only supports one level. Mounting all subsystem into /sys/fs/cgroup, which i tried is more problematic then different mountpoints. You will not be able to put programs in different groups for different subsystems etc.

Alessandro Ghedini

May this be supported as a fallback? It would be nice if ulatencyd worked in this situation (maybe after printing a warning) without aborting. The default behaviour would remain the same.

Daniel Poelzleithner
Owner

yes, that could be done, but requires duplicaton of rules. where is the discussion going on, so i could throw my 2cents at it :-)

Alessandro Ghedini

The discussion about mounting cgroup by default is here (now that you ask it seems dead...), while the report about ulatencyd not working with it is linked above.

Even if the discussion about mounting cgroup by default goes nowhere, someone still do that using fstab along with ulatencyd, should I simply suggest to stop doing it?

Ritesh Raj Sarraf

Any update on this bug?

The discussion pointed by AlexBio is for enabling cgroup automount at mount point /sys/fs/cgroup

The current approach that ulatency takes makes it incompatible with the rest. At least, Linux Containers, it expects cgroup to be mounted at /sys/fs/cgroup , making it difficult to use lxc and ulatency at the same time.
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=645995

Daniel Poelzleithner
Owner
Ritesh Raj Sarraf
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