Re: [PATCH] Load balancing problem in 2.6.2-mm1

Nick Piggin
2004-02-06T22:59:38Z

Martin J. Bligh wrote:

>>>It's the classic fairness vs throughput thing we've argued about before.
>>>Most workloads don't have that static a number of processes, but it
>>>probably does need to do it if the imbalance is persistent ... but much
>>>more reluctantly than normal balancing. See the patch I sent out a bit
>>>earlier to test it - that may be *too* extreme in the other direction,
>>>but it should confirm what's going on, at least.
>>>
>>Yep. I've argued for fairness here, and that is presently what
>>we get. Between nodes the threshold should probably be higher
>>though.
>>
>
>OK, but do you agree that the rate we rebalance things like 2 vs 1 should
>be slower than the rate we rebalance 3 vs 1 ? Fairness is only relevant
>over a long term imbalance anyway, so there should be a big damper on
>"fairness only" rebalances.
>
>

Well presently it happens at the same rate. This isn't bad though,
because you just use the more conservative rate. Its probably not
worth distinguishing the two cases.

If a CPU becomes idle, it will attempt to balance immediately.

>Moreover, as Rick pointed out, it's particularly futile over idle cpus ;-)
>
>

I don't follow...