[rfc] bind per-cpu timeout threads to each CPU

[Peter Grehan]

> Yup. I've just done that.
>
> http://people.freebsd.org/~adrian/norse/20140509-swi-pin-1.diff

  Thanks, that'll work.

> Which workloads are you thinking about? Maybe we could introduce some
> higher level description of which CPU(s) at boot time to do "freebsd
> stuff" on, and then don't start things like pcpu swi's and NIC threads
> on those CPUs.

  A classic case is partitioning cores into control and data plane 
groups. I'm sure there are lots more. What's nice about cpuset is that 
the choice and change can be dynamic, so long as there aren't pinned 
threads in the default set.

  An option to restrict FreeBSD pCPU threads to a subset could be useful.

> Can you think of situations where we'd want to have per-cpu swi's even
> _running_ for CPUs that you want to dedicate to other things? There's
> nothing stopping you from scheduling a callout on a different target
> CPU.

  At least for the uses I know, it's complete isolation from other 
processing, kernel threads included. The 'freebsd stuff' info you 
mentioned should be sufficient.

later,

Peter.