Vax interlock insn's (Re: Please do not yell at people for trying to help you.)

[Anders Magnusson <ragge%ludd.ltu.se@localhost>]

(a little side-note, but may be interesting)

On 11/13/2010 04:17 AM, Matt Thomas wrote:
> Eventually, most operations come down to compare and swap.  It's just too
> damn useful to not have as a primitive.  Even if some of the platforms
> have to emulate it somehow.  Just because an architecture is 30+ years old
> doesn't mean we are forced to ignore algorithms that came after its birth.
>
> The VAX now has a fast non-MP emulation of atomic_cas so that should be
> less of an issue.
>    
When I tested NetBSD/vax MP on an 8353 some years ago I found that
it ended up unexpectedly slow in some situations.  Some timing showed
that the interlock insn's were _really_ slow compared to their 
non-interlocked
version; insqti almost took 100 times of insque, bbssi were not that slow
compared to bbss but there were an unreasonable amount of time spent
on the buses.

Using an MP VAX were just not worth it (at least not with BI bus).  Better
to optimize for UP VAX and make it work reasonable good.

-- Ragge