Re: revivesa status 2008/07/09

[Thor Lancelot Simon <tls%rek.tjls.com@localhost>]

On Fri, Jul 11, 2008 at 09:30:13PM +0200, Manuel Bouyer wrote:
> On Fri, Jul 11, 2008 at 12:47:45PM +0000, Andrew Doran wrote:
> > 
> > In its current form SA threading is a regressive proposition. Even if all
> > the remaining issues are addressed, what benefits would it bring over and
> > above 1:1 threading?
> 
> Be able to run a netbsd-4 or netbsd-3 userland on a netbsd-5 kernel.

I think there's another significant benefit: it should give a significant,
possibly even huge, performance benefit for multithreaded applications on
platforms which are uniprocessor and have a significant penalty for
context-switching into the kernel.

The obvious example is ARM -- and there are a _lot_ of ARM CPUs out
there in the world in embedded devices, often running software that makes
heavy use of threading for its UI.  There are pretty well-understood reasons
why SA actually does win in this kind of use case, and it's not an
unimportant one for NetBSD.  And there are a number of new low- and mid-
range network processors and "storage" processors showing up this year
which are ARM based and will run NetBSD with few or no changes, which is
sadly not the case for a lot of the modern MIPS or PowerPC choices in that
space.

If I saw a benchmark -- and not an I/O bound one -- from such a platform
where the 1:1 threading did anywhere near as well as the SA threading I'd
certainly change my mind, but...

-- 
Thor Lancelot Simon                                        
tls%rek.tjls.com@localhost
 "My guess is that the minimal training typically provided would only
 have given the party in question multiple new and elaborate ways to do
 something incomprehensibly stupid and dangerous."      -Rich Goldstone