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From: Erich Focht <efocht@ess.nec.de>
To: "Martin J. Bligh" <mbligh@aracnet.com>,
       Michael Hohnbaum <hohnbaum@us.ibm.com>
Subject: Re: [Lse-tech] Minature NUMA scheduler
Date: Mon, 13 Jan 2003 00:35:00 +0100
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On Friday 10 January 2003 17:57, Martin J. Bligh wrote:
> This seems like the right approach to me, apart from the trigger to
> do the cross-node rebalance. I don't believe that has anything to do
> with when we're internally balanced within a node or not, it's
> whether the nodes are balanced relative to each other. I think we should
> just check that every N ticks, looking at node load averages, and do
> a cross-node rebalance if they're "significantly out".

OK, I changed my mind about the trigger and made some experiments with
the cross-node balancer called after every N calls of
load_balance. If we make N tunable, we can even have some dynamics in
case the nodes are unbalanced: make N small if the current node is
less loaded than the average node loads, make N large if the node is
averagely loaded. I'll send the patches in a separate email.

> The NUMA rebalancer
> is obviously completely missing from the current implementation, and
> I expect we'd use mainly Erich's current code to implement that.
> However, it's suprising how well we do with no rebalancer at all,
> apart from the exec-time initial load balance code.

The fact that we're doing fine on kernbench and numa_test/schedbench
is (I think) understandeable. In both benchmarks a process cannot
change its node during its lifetime, therefore has minimal memory
latency. In numa_test the "disturbing" hackbench just cannot move away
any of the tasks from their originating node. Therefore the results
are the best possible.

Regards,
Erich

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