On 21 Nov, 2014, at 00:22 , Eduardo Horvath <e...@netbsd.org> wrote:
> Or you could try to get the kernel to run on a SPARC V9 machine running
> with RMO memory ordering. There's a lot more of those around. I'm not
> convinced the existing APIs are sufficient to get that working.
It would be worrying if the kernel wouldn't run that way. The table from
the McKenney paper, reproduced here
http://en.wikipedia.org/wiki/Memory_ordering
indicates that SPARC RMO potentially reorders the same operations as
ARMv7 and POWER. Someone else would have to comment on how well NetBSD
runs on multiprocessor versions of the latter processors, but it is supposed
to and I haven't noticed any code which omits required barriers for machines
like that (unlike the Alpha, where missing barriers for its unique quirk are
easy to find). The API seems sufficient.
Beyond the Alpha-barrier, he only thing I find lacking about the membar_*()
API is maybe a set of functions that would eliminate the #ifndef/#endif
around
#ifndef __HAVE_ATOMIC_AS_MEMBAR
membar_foo();
#endif
repeated over and over when synchronization is done via atomic_ops(3).
Dennis Ferguson
