Re: [RFC] CPU hard limits

[Avi Kivity <avi@redhat.com>]

Bharata B Rao wrote:
> 2. Need for hard limiting CPU resource
> --------------------------------------
> - Pay-per-use: In enterprise systems that cater to multiple clients/customers
>   where a customer demands a certain share of CPU resources and pays only
>   that, CPU hard limits will be useful to hard limit the customer's job
>   to consume only the specified amount of CPU resource.
> - In container based virtualization environments running multiple containers,
>   hard limits will be useful to ensure a container doesn't exceed its
>   CPU entitlement.
> - Hard limits can be used to provide guarantees.
>   
How can hard limits provide guarantees?

Let's take an example where I have 1 group that I wish to guarantee a 
20% share of the cpu, and anther 8 groups with no limits or guarantees.

One way to achieve the guarantee is to hard limit each of the 8 other 
groups to 10%; the sum total of the limits is 80%, leaving 20% for the 
guarantee group. The downside is the arbitrary limit imposed on the 
other groups.

Another way is to place the 8 groups in a container group, and limit 
that to 80%. But that doesn't work if I want to provide guarantees to 
several groups.

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