[cap-talk] Cap type safe OS questions

[Sam Mason]

On Sun, Aug 02, 2009 at 09:39:05PM +0200, Rob Meijer wrote:
> Most probably an extremely ignorant question, but with the number of cores
> in modern systems, why is this still an issue? I would imagine if context
> switches have a high cost, running the kernel on different cores than the
> user space processes would be the logical way to go.

Hum, interesting question.  Not sure if this was specifically addressed
to me or not; but I'll respond anyway.  I'd guess that the kernel never
really spends any useful amount of time actually executing and hence
devoting a core entirely to the kernel has always seemed wasteful.
Coordination between cores is fiddly and is normally done by sending
the other an IPI to bring it back to kernel from user space.  If you've
dedicated a core to this you may be able to get away from IPIs, latency
still seems like a killer though.

Context switches take on the order of a microsecond, I'm can't seem
to find out where time is spent on an IPI but I'd imagine it would be
similar order of magnitude.

-- 
  Sam  http://samason.me.uk/