Fedora 16 Cgroups

[Mick Farmer]

Dear GLLUGers,

Do I need to keep cgroups on my machine?

I'd like to remove them if possible.

Regards,

Mick

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[Martin A. Brooks]

Post by Mick Farmer
Do I need to keep cgroups on my machine?
I'd like to remove them if possible.

What is cgroups doing that's in your way?



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[Martin A. Brooks]

Post by Martin A. Brooks

Post by Mick Farmer
Do I need to keep cgroups on my machine?
I'd like to remove them if possible.

What is cgroups doing that's in your way?

...

It probably shows my age! At work, we started with Mini-Unix before
getting in the Unix groove with versions 6 and 7.
It was all so much simpler in those days. I used John Lion's book to
teach my students operating systems. Dennis sent updates on RK05 disks.
I knew the binary for the bootstrap loader by heart.
Now we have virtual systems with logical volumes and control groups and
something tells me I want to go back to a easily configurable physical
system rather than accept the bloat we now have with Windows and its
friends.

So, what is cgroups doing that's in your way?




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[John Hearns]

This reminds me. Maybe if there is another meeting I should do a talk on
cpusets.

[Richard W.M. Jones]

Post by Mick Farmer
Do I need to keep cgroups on my machine?

Yes and no. As with SELinux you're paying a (very small) penalty just
by having them compiled into the kernel, so you'd also have to compile
your own kernel. The time taken to compile and deal with a custom
kernel outweighs any possible savings.

Rich.

[Nix]

Post by Richard W.M. Jones
Yes and no. As with SELinux you're paying a (very small) penalty just
by having them compiled into the kernel, so you'd also have to compile
your own kernel. The time taken to compile and deal with a custom
kernel outweighs any possible savings.

Is it really that hard with a modern distro? I've built my own kernels
for fifteen years now, but then I don't use Fedora so I can't say if
it's harder to get a working kernel on there than on other systems.
(Yes, you need a working initial ramdisk, but dracut can build those
without much effort, even if you have your own kernel, and
/sbin/installkernel does that, doesn't it? So 'make install' from the
kernel source tree should just do the right thing.)

[Richard W.M. Jones]

Post by Nix

Post by Richard W.M. Jones
Yes and no. As with SELinux you're paying a (very small) penalty just
by having them compiled into the kernel, so you'd also have to compile
your own kernel. The time taken to compile and deal with a custom
kernel outweighs any possible savings.

Is it really that hard with a modern distro? I've built my own kernels
for fifteen years now, but then I don't use Fedora so I can't say if
it's harder to get a working kernel on there than on other systems.
(Yes, you need a working initial ramdisk, but dracut can build those
without much effort, even if you have your own kernel, and
/sbin/installkernel does that, doesn't it? So 'make install' from the
kernel source tree should just do the right thing.)

I didn't say it was hard, I said the time spent compiling the kernel
and manually updating it would outweigh the miniscule savings from not
having the overhead of cgroups :-)

Rich.

[Mick Farmer]

Dear Richard,

Is it possible to leave the cgroups code in the kernel, but just turn
off using it?

Regards,

Mick

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[Richard W.M. Jones]

Post by Mick Farmer
Dear Richard,
Is it possible to leave the cgroups code in the kernel, but just turn
off using it?

Sure! Just unmount /sys/fs/cgroup. Certainly systemd and libvirt are
written to ignore cgroups if this directory isn't mounted.

However I wonder why you'd want to do this. cgroups isn't some sort
of module in the kernel which does nothing when it's not used. It's
an invasive set of changes that affect just about every important
kernel structure, so if you're using processes or networks, you're
using cgroups even if you're not using any features of it.

It could be better to learn cgroups. It's a reasonably neat and
sensible partitioning and resource allocation feature.

Rich.

[Nix]

Post by Richard W.M. Jones
It could be better to learn cgroups. It's a reasonably neat and
sensible partitioning and resource allocation feature.

... which is about to get crippled by removing the option to have more
than one sort of cgroup active at once, on the grounds that systemd
doesn't need it so of course nobody else does. :/

[Martin A. Brooks]

Post by Richard W.M. Jones
It could be better to learn cgroups. It's a reasonably neat and
sensible partitioning and resource allocation feature.

Even would be to completely ignore it, unless something is getting in your
way.

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