Re: Kernel preemption

[David Holland <dholland-tech%netbsd.org@localhost>]

On Fri, Apr 25, 2008 at 08:13:34PM +0100, Andrew Doran wrote:
 > The below patch implments in-kernel preemption for the i386 port.

Is in-kernel preemption really worthwhile on multiprocessor machines?

Given fine-grained locking it's not clear that it really helps much
with scheduler latency, and it adds potentially quite a bit of
overhead because you have to fiddle with interrupts for all spinlocks
rather than just those that are touched by interrupt code. Plus it
makes per-cpu stuff that much harder to work with.

The last time I thought hard about this (about a year ago) I concluded
it wasn't really a good idea, but I'm open to corrections.

-- 
David A. Holland
dholland%netbsd.org@localhost