Re: [RFC] (How to) Let idle CPUs sleep

[Srivatsa Vaddagiri <vatsa@in.ibm.com>]

On Thu, May 12, 2005 at 08:08:26PM +0200, Martin Schwidefsky wrote:
> I would prefer a solution where the busy CPU wakes up an idle CPU if the
> imbalance is too large. Any scheme that requires an idle CPU to poll at
> some intervals will have one of two problem: either the poll intervall
> is large then the imbalance will stay around for a long time, or the
> poll intervall is small then this will behave badly in a heavily
> virtualized environment with many images.

I guess all the discussions we are having boils down to this: what is the max
time one can afford to have an imbalanced system because of sleeping idle CPU
not participating in load balance? 10ms, 100ms, 1 sec or more?

Maybe the answer depends on how much imbalance it is that we are talking of
here. A high order of imbalance would mean that the sleeping idle CPUs have
to be woken up quickly, while a low order imbalance could mean that 
we can let it sleep longer.

>From all the discussions we have been having, I think a watchdog
implementation makes more sense. Nick/Ingo, what do you think
should be our final decision on this?



-- 


Thanks and Regards,
Srivatsa Vaddagiri,
Linux Technology Center,
IBM Software Labs,
Bangalore, INDIA - 560017