systemd and cgroups: heads up

[Daniel J Walsh]

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On 08/26/2010 01:18 PM, Daniel P. Berrange wrote:
> On Thu, Aug 26, 2010 at 01:04:33PM -0400, Daniel J Walsh wrote:
>>
>> I don't know.  My goal with sandbox was to allow users to startup
>> sandboxes in such a way that they could be still killed.
>>
>> Is there a way in cgroups to say
>>
>> dwalsh gets 80% CPU
>> Then allow dwalsh to specify sandboxes can only use 80% of His CPU.  So
>> he can kill them.
> 
> You can't directly specify absolute CPU%. You can only set relative
> prioritization between groups via the 'cpu_shares' tunable. A group
> with double the 'cpu_shares' value will get twice as much running
> time from the schedular. If you know all groups at a particular
> level of the hierarchy you can calculate the relative shares 
> required to give the absolute 80% value, but it gets increasingly
> "fun" to calculate as you add more groups/shares :-)
> 
> eg with 2 cgroups
> 
>  group1:  cpu_shares=1024  (20%)
>  group2:  cpu_shares=4096  (80%)
> 
> With 3 groups
> 
>  group1:  cpu_shares=512  (10%)
>  group2:  cpu_shares=512  (10%)
>  group3:  cpu_shares=4096  (80%)
> 
> Or with 3 groups
> 
>  group1:  cpu_shares=342  (6.66%)
>  group1:  cpu_shares=682  (13.34%)
>  group2:  cpu_shares=4096 (80%)
> 
> 
> 
> Regards,
> Daniel

Seems we have a new hammer and everyone is looking to use.  So far
systemd, sandbox, libvirt and chrome-sandbox are using it.  Which
probably is not going to get the results we want.

Since systemd goal might be to make sure no user uses more then X% of
memory/CPU/ or setup CPU afinity.  But sandbox and chrome-sandbox might
allow you to use more.

Which is why I think the kernel needs to allow nesting of cgroups.
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