Date: Mon, 21 Jan 2002 00:59:41 +0100 (CET) From: Michal Mertl <mime@traveller.cz> To: Garrett Wollman <wollman@khavrinen.lcs.mit.edu> Cc: arch@FreeBSD.ORG Subject: Re: 64 bit counters again Message-ID: <Pine.BSF.4.41.0201210058340.94442-100000@prg.traveller.cz> In-Reply-To: <200201202125.g0KLPqf31593@khavrinen.lcs.mit.edu>
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On Sun, 20 Jan 2002, Garrett Wollman wrote: > I hope you'll forgive me for reopening this up to -arch again.... > > <<On Sat, 19 Jan 2002 21:20:26 +0100 (CET), Michal Mertl <mime@traveller.cz> said: > > > But compare and exchange or conditional move insns should be there. > > And because the platform is fully 64 bit AFAIK I'd expect at least > > 64 bit variants of them. The cache coherency problem is also > > unrelated - it's there whatever size you have. > > The ultimate upshot of this is that it does not make sense to expose > low-level primitives (such as compare-exchange or LL/SC) directly in > the API. This is because each processor architecture will have its It isn't exposed in the API as far as I see. > own requirements for coherency, in some cases requiring specialized > instructions which a compiler would not normally generate, and often > requiring memory barriers inside the spin loop. > > However, we can easily define a set of basic operations which every > architecture we currently support can implement reliably and > coherently without locking, including incrementing counters and > updating some kinds of linked lists. (This has been proven both > formally and by construction; see a recent Algorithms textbook.) Seems so. -- Michal Mertl mime@traveller.cz To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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