[yocto] linux-yocto-rt and cgroups

[Bruce Ashfield]

On 13-06-23 3:48 PM, Paul D. DeRocco wrote:
> I built core-image-base with Tom Zanussi's Cedartrail BSP for Dylan, which
> worked fine. (Thanks, Tom.) Then, I switched over to linux-yocto-rt, and it
> still worked fine. Then, I tried to switch to systemd, and it complains
> bitterly on startup that there is no cgroup support in the kernel.
>
> I'd like to use an RT kernel, so that I can squeeze out as many notes as
> possible (it's a musical instrument) before getting sound driver underruns.
> And I'd like to use systemd, so that it boots fast. Do I have to choose one
> or the other? Is there some reason cgroups are left out of linux-yocto-rt?
> If not, is there an easy way to put it back in, without becoming an expert
> in kernel configuration?

There's no technical reason at all. In fact, pre 3.8 the -rt kernel used
to inherit more of the standard kernel's configuration and hence enabled
cgroups. In 3.8, we defined a new policy for the -rt kernel, that used
parts of the standard kernel's configuration, but not all.

We can definitely add functionality to this baseline, and I'll be adding
more in the upcoming dev cycle for yocto 1.5.

In the meantime you can enable it, and let me know how it goes. I can then
update the -rt baseline config, knowing that someone else is testing it
too.

To enable it, create a linux-yocto_3.8.bbappend, and add:

  KERNEL_FEATURES_append = " features/cgroups/cgroups.scc"

And you'll get the same cgroups config that you have with the standard
linux-yocto kernel.

Cheers,

Bruce

>