Re: [Lse-tech] Re: NUMA scheduler 2nd approach

Andrew Theurer
2003-01-14T04:28:15Z

> Erich,
>
> I played with this today on my 4 node (16 CPU) NUMAQ. Spent most
> of the time working with the first three patches. What I found was
> that rebalancing was happening too much between nodes. I tried a
> few things to change this, but have not yet settled on the best
> approach. A key item to work with is the check in find_busiest_node
> to determine if the found node is busier enough to warrant stealing
> from it. Currently the check is that the node has 125% of the load
> of the current node. I think that, for my system at least, we need
> to add in a constant to this equation. I tried using 4 and that
> helped a little.

Michael,

in:

+static int find_busiest_node(int this_node)
+{
+ int i, node = this_node, load, this_load, maxload;
+
+ this_load = maxload = atomic_read(&node_nr_running[this_node]);
+ for (i = 0; i < numnodes; i++) {
+ if (i == this_node)
+ continue;
+ load = atomic_read(&node_nr_running[i]);
+ if (load > maxload && (4*load > ((5*4*this_load)/4))) {
+ maxload = load;
+ node = i;
+ }
+ }
+ return node;
+}

You changed ((5*4*this_load)/4) to:
(5*4*(this_load+4)/4)
or
(4+(5*4*(this_load)/4)) ?

We def need some constant to avoid low load ping pong, right?

Finally I added in the 04 patch, and that helped
> a lot. Still, there is too much process movement between nodes.

perhaps increase INTERNODE_LB?

-Andrew Theurer