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Draft - Cgroups and vservers

to make cgroups works with vserver your kernel must have the following settings:

# CONFIG_CGROUP_NS is not set

Or in the menu:

[*] Control Group support                               [ ]   Example debug cgroup subsystem
[ ]   Namespace cgroup subsystem
[*]   control group freezer subsystem
[*]   Device controller for cgroups
[*]   Cpuset support
[*] Group CPU scheduler
[*]   Group scheduling for SCHED_OTHER
[ ]   Group scheduling for SCHED_RR/FIFO
      Basis for grouping tasks (Control groups)  --->
[*] Simple CPU accounting cgroup subsystem
[*] Resource counters
[*] Memory Resource Controller for Control Groups

Note about this from the list:

> > I currently have the CONFIG_CGROUP_NS option set in my kernels. Does  
> > this mean add extra namespace support, or I am preventing the Cgroup  
> > based scheduling from working by enabling it? Should I unset it and  
> > rebuild?

yes, with CGROUP_NS enabled, you basically block
the 'normal' cgroup scheduling which is used by
util-vserver, and have to handle the croup namespace
yourself ...

You must have the /dev/cgroup mounted with the 'cpu' option. For exemple for cpuset, memory and cpu cgroup handling:

(root)> grep cgroup  /etc/fstab
cpuset  /dev/cgroup     cgroup  rw,cpuset,cpu,memory    0       0

Then you must create on you guest /etc/vservers/<guest>/cgroup/ all the files put here will be copied to the guest cgroup when created. The doc for cgroup is not on the great flower page but in the source of the latests utils. You can have a default cgroup directory for all guest that can be overrided by each guest's cgroup directory.

Draft - Distributing cpu shares with cgroups

From what i gathered in sched-design-CFS.txt [1]

This is simply done by adjusting the cpu.shares. Just do:

echo '512' > /dev/cgroup/<guest name>/cpu.shares

The share you get is equal to the guest's share divided by the sum of the cpu shares of all the guest. So for exemple :

vserver guest 1 => 512   
vserver guest 2 => 512
vserver guest 3 => 2048
vserver guest 4 => 512

so you have a total of 3584 cpu shares (2048+512+512+512) , then you get :

vserver guest 1 => 512 / 3584 = 14%  cpu
vserver guest 2 => 512 / 3584 = 14%  cpu
vserver guest 3 => 2048 / 3584 = 57% cpu
vserver guest 4 => 512 / 3584 = 14%  cpu

Note that this is fair scheduling and this will not enfore HARD limit (as far as i know).

Making share permanent with util vserver

You must use the "cgroup" directory. You can apply defaults to all vservers or choose different settings for each guest:

  • /etc/vservers/.default/cgroup , this directory contains settings applying to all guest when they start
  • /etc/vservers/<guestname>/cgroup , this directory contains settings for the guest when it starts.

Exemple :

mkdir /etc/vservers/.defaults/cgroup
mkdir /etc/vservers/<guestname>/cgroup
echo '2048' > /etc/vservers/<guestname>/cgroup/cpu.shares
# List of CPUs
echo 1 > /etc/vservers/<guestname>/cgroup/cpuset.cpus
# NUMA nodes
echo 1 > /etc/vservers/<guestname>/cgroup/cpuset.mems

Note that /etc/vservers is an exemple, in my Aqueos install i use /usr/local/etc/vservers but /etc/vservers seems to be the defaults for the classic installs.

Regards, Ghislain.

cgroup and CFS based CPU hard limiting that replaces sched_hard

This feature is currently available in patch- and is in testing phase as of this patch set so report any bugs to the mailing list.

Example for an upper bound of 2/5th (or 40%) of the all cpu power that a guest/cgroup can use :

# force CFS hard limit
echo 1 > /etc/vservers/<guestname>/cgroup/cpu.cfs_hard_limit
# time assigned to guest (in microseconds) 200000 = 0,2 sec 
echo 200000 > /etc/vservers/<guestname>/cgroup/cpu.cfs_runtime_us
# in each specified period (in microseconds) 500000 = 0,5 sec 
echo 500000 > /etc/vservers/<guestname>/cgroup/cpu.cfs_period_us

This limit is an hard limit, see it like an upper wall for the ressources used by the cgroup. If you set both cpu share AND hard limit the system will do fine but hard limits takes priority over cpu share scheduling, so cpu share will do the job but each cgroup will have an upper bound that it cannot cross even if the cpu share you gived it is higher.

  Hard limit feature adds 3 cgroup files for CFS group scheduler:
cfs_runtime_us: Hard limit for the group in microseconds.
cfs_period_us: Time period in microseconds within which hard limits is enforced.
cfs_hard_limit: The control file to enable or disable hard limiting for the group.

real world exemples of scheduling

this part is to be filled with exemple you have put in place and are working and have been tested, please add the patch and kernel version for each exemple you put here.

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