Date: Fri, 17 Oct 2003 00:11:35 +0200 From: "Poul-Henning Kamp" <phk@phk.freebsd.dk> 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: <55345.1066342295@critter.freebsd.dk> In-Reply-To: Your message of "Thu, 16 Oct 2003 21:16:17 %2B1000." <20031016210328.T930@gamplex.bde.org>
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In message <20031016210328.T930@gamplex.bde.org>, Bruce Evans writes: >> * 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. There are _so_ many things which explode if this assumption does not hold that I think doing anything but gold-plating it would be a total waste of time. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.
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