Hi Martin & Michael,

as discussed on the LSE call I played around with a cross-node
balancer approach put on top of the miniature NUMA scheduler. The
patches are attached and it seems to be clear that we can regain the
good performance for hackbench by adding a cross-node balancer.

The patches are:

01-minisched-2.5.55.patch : the miniature scheduler from
Martin. Balances strictly within a node. Added an inlined function to
make the integration of the cross-node balancer easier. The added code
is optimised away by the compiler.

02-initial-lb-2.5.55.patch : Michael's initial load balancer at
exec().

03-internode-lb-2.5.55.patch : internode load balancer core. Called
after INTERNODE_LB calls of the inter-node load balancer. The most
loaded node's cpu-mask is ORed to the own node's cpu-mask and
find_busiest_in_mask() finds the most loaded CPU in this set.

04-smooth-node-load-2.5.55.patch : The node load measure is smoothed
by adding half of the previous node load (and 1/4 of the one before,
etc..., as discussed in the LSE call). This should improve a bit the
behavior in case of short timed load peaks and avoid bouncing tasks
between nodes.

05-var-intnode-lb2-2.5.55.patch : Replaces the fixed INTERNODE_LB
interval (between cross-node balancer calls) by a variable
node-specific interval. Currently only two values used. Certainly
needs some tweaking and tuning.

01, 02, 03 are enough to produce a working NUMA scheduler, when
including all patches the behavior should be better. I made some
measurements which I'd like to post in a separate email tomorrow.

Comments? Ideas?

Regards,
Erich