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From: cet1@cl.cam.ac.uk (C.E. Thompson)
Newsgroups: comp.lang.asm370
Subject: Re: More pet ALC tricks...
Message-ID: <1654@gannet.cl.cam.ac.uk>
Date: 14 Nov 89 22:16:17 GMT
References: <8911131336.AA27002@brazos.rice.edu>
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Reply-To: cet1@cl.cam.ac.uk (C.E. Thompson)
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Organization: U of Cambridge Comp Lab, UK
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In article <8911131336.AA27002@brazos.rice.edu>,P85025@BARILVM.BITNET (Doron Shikmoni) writes
>Note, that CS/CDS/TS should be used only if you really need to serialize;
>if you just want to compare-and-then-swap, and think of using these since
>"It's one instruction", in a simple "application" program, don't; these
>instructions are expensive.

Well, they are not as cheap as L and C, say, but you shouldn't be paranoid
about using them, either. On CPUs with write-in caches, the overheads are
not that bad. It makes sense to use CS/CDS to synchronise between a program
and an asynchronous exit, for example, using them for their non-divisibility
rather than their MP-storage-consistency. 

Chris Thompson
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