For a forthcoming NUMA box that uses Foster processors and IBM's Summit
chipset, I've had to extend Martin Bligh's multiquad code beyond the usual
APIC flat mode and his clustered logical mode. The problem with the latter
is that Intel's new APIC numbering scheme only puts two physical CPUs per
cluster. Linux leaves all the TPRs and XTPRs at zero, so that means that all
the interrupts will hit just one CPU per cluster, and generally everything
goes to one cluster.
To combat that, I used the XAPICs new physical cluster capability and a
simple (probably too simple) static round robin binding to roughly level out
the interrupt load. This works, though it seems somehow unsatisfying. The
alternative is much more invasive: adding interrupt code to adjust XTPRs,
hacks to the scheduler to somehow encapsulate task priority in 4 bits, etc.
What do you think?
-- James Cleverdon, IBM xSeries Platform (NUMA), Beaverton jamesclv@us.ibm.com | cleverdj@us.ibm.com
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