Date: 16 Oct 2003 12:36:12 +0100 From: Doug Rabson <dfr@nlsystems.com> To: Bruce Evans <bde@zeta.org.au> Cc: cvs-all@freebsd.org Subject: Re: cvs commit: src/sys/sys bus.h kobj.h param.h src/sys/kern subr_bus.c subr_kobj.c Message-ID: <1066304172.20052.8.camel@builder02.qubesoft.com> In-Reply-To: <20031016210328.T930@gamplex.bde.org> References: <200310160916.h9G9GSqQ067982@repoman.freebsd.org> <20031016210328.T930@gamplex.bde.org>
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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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