Re: [RFC 0/5] sched: Add CPU rate caps

[Mike Galbraith]

On Fri, 2006-05-26 at 14:20 +1000, Peter Williams wrote:
> These patches implement CPU usage rate limits for tasks.
> 
> 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 killer problem I see with this approach is that it doesn't address
the divide and conquer problem.  If a task is capped, and forks off
workers, each worker inherits the total cap, effectively extending same.

IMHO, per task resource management is too severely limited in it's
usefulness, because jobs are what need managing, and they're seldom
single threaded.  In order to use per task limits to manage any given
job, you have to both know the number of components, and manually
distribute resources to each component of the job.  If a job has a
dynamic number of components, it becomes impossible to manage.

	-Mike

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