Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]

Chris Friesen
2007-04-17T15:53:03Z

Peter Williams wrote:
> Chris Friesen wrote:
>> Scuse me if I jump in here, but doesn't the load balancer need some
>> way to figure out a) when to run, and b) which tasks to pull and where
>> to push them?

> Yes but both of these are independent of the scheduler discipline in force.

It is not clear to me that this is always the case, especially once you
mix in things like resource groups.

> If
> the load balancer manages to keep the weighted (according to static
> priority) load and distribution of priorities within the loads on the
> CPUs roughly equal and the scheduler does a good job of ensuring
> fairness, interactive responsiveness etc. for the tasks within a CPU
> then the result will be good system performance within the constraints
> set by the sys admins use of real time priorities and nice.

Suppose I have a really high priority task running. Another very high
priority task wakes up and would normally preempt the first one.
However, there happens to be another cpu available. It seems like it
would be a win if we moved one of those tasks to the available cpu
immediately so they can both run simultaneously. This would seem to
require some communication between the scheduler and the load balancer.

Certainly the above design could introduce a lot of context switching.
But if my goal is a scheduler that minimizes latency (even at the cost
of throughput) then that's an acceptable price to pay.

Chris