cvs commit: src/sys/sys bus.h kobj.h param.h src/sys/kern
subr_bus.c subr_kobj.c
Doug Rabson
dfr at nlsystems.com
Thu Oct 16 04:36:28 PDT 2003
On Thu, 2003-10-16 at 12:16, Bruce Evans wrote:
> On Thu, 16 Oct 2003, Doug Rabson wrote:
>
> > dfr 2003/10/16 02:16:28 PDT
> >
> > FreeBSD src repository
> >
> > Modified files:
> > sys/sys bus.h kobj.h param.h
> > sys/kern subr_bus.c subr_kobj.c
> > Log:
> > * Add multiple inheritance to kobj. Each class can have zero or more base
> > ...
> > * Change the kobj method lookup algorithm to one which is SMP-safe. This
> > relies only on the constraint that an observer of a sequence of writes
> > of pointer-sized values will see exactly one of those values, not a
> > mixture of two or more values. This assumption holds for all processors
> > which FreeBSD supports.
>
> This assumption should be avoided by using atomic_load() (and
> atomic_store_mumble()). See a discussion of "atomicity of unlocked
> reads" last month. First implement atomic_load(). There is currently
> only atomic_load_acq_<type>(). "acq" gives acquire semantics which
> is more than what is needed here and our implementations may do more
> than what is required anyway for some arches. "<type>" is part of a
> bad API.
Without using something like <type>, how can you know how much to read
(without abusing some kind of GCC language extension)? I don't want to
use atomic_load_acq_* since I don't care which order values are written
to the cache.
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