Re: Table duplication on smp machine

[Thomas Heinz <creatix@hipac.org>]

Hi Patrick

You wrote:
> There are other, generic APIs for allocation of per-cpu data. In a new
> world, the rare match/target module with such a requirement, could use
> that API.

Ok but with the current scheme I don't see any reason why a match/target
would want to write to per-cpu data. Is there any practical application
for this?

> But there is another, less common, incentive to have per-cpu copies
> of all the data structures: non-uniform-memory-architecture machines.
> An example (hopefully) not far from widespread adoption, would be the
> new AMD Hammer SMP architecture. On such an architecture, there is
> a performance benefit even from CPU (or node) local copies of even
> readonly data, because of the reduced local memory latency. In the
> Hammer example, there would be one copy of the ruleset in each
> single Hammer's locally attached DRAM.
> 
> Not so common today, but I always thought that the existing separation
> in the current iptables code was good preparation for that future.

Very interesting. I guess one has to use a special API to address the
per cpu memory so that the current implementation wouldn't work out
of the box. Right?


Regards,

Thomas