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Re: revivesa status 2008/07/09

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

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                               
 "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

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