Re: [RFC] CPU hard limits

Avi Kivity
2009-06-07T06:06:57Z

Bharata B Rao wrote:
> On Fri, Jun 05, 2009 at 09:01:50AM +0300, Avi Kivity wrote:
>
>> Bharata B Rao wrote:
>>
>>> But could there be client models where you are required to strictly
>>> adhere to the limit within the bandwidth and not provide more (by advancing
>>> the bandwidth period) in the presence of idle cycles ?
>>>
>>>
>> That's the limit part. I'd like to be able to specify limits and
>> guarantees on the same host and for the same groups; I don't think that
>> works when you advance the bandwidth period.
>>
>> I think we need to treat guarantees as first-class goals, not something
>> derived from limits (in fact I think guarantees are more useful as they
>> can be used to provide SLAs).
>>
>
> I agree that guarantees are important, but I am not sure about
>
> 1. specifying both limits and guarantees for groups and
>

Why would you allow specifying a lower bound for cpu usage (a
guarantee), and upper bound (a limit), but not both?

> 2. not deriving guarantees from limits.
>
> Guarantees are met by some form of throttling or limiting and hence I think
> limiting should drive the guarantees

That would be fine if it didn't idle the cpu despite there being demand
and available cpu power.

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.