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SubjectRe: [RFC 0/5] sched: Add CPU rate caps
Con Kolivas wrote:
> On Friday 26 May 2006 14:20, Peter Williams wrote:
>> These patches implement CPU usage rate limits for tasks.
>
> Nice :)

Thanks.

>
>> Although the rlimit mechanism already has a CPU usage limit (RLIMIT_CPU)
>> it is a total usage limit and therefore (to my mind) not very useful.
>> These patches provide an alternative whereby the (recent) average CPU
>> usage rate of a task can be limited to a (per task) specified proportion
>> of a single CPU's capacity. The limits are specified in parts per
>> thousand and come in two varieties -- hard and soft.
>
> Why 1000?

Probably a hang over from a version where the units were proportion of a
whole machine. Percentage doesn't work very well if there are more than
1 CPU in that case (especially if there are more than 100 CPUs :-)).
But it's also useful to have the extra range if your trying to cap
processes (or users) from outside the scheduler using these primitives.

> I doubt that degree of accuracy is possible in cpu accounting and
> accuracy or even required. To me it would seem to make more sense to just be
> a percentage.
>

It's not meant to imply accuracy :-). The main issue is avoiding
overflow when doing the multiplications during the comparisons.

Peter
--
Peter Williams pwil3058@bigpond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
-- Ambrose Bierce
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