chapter5-m3-ziavras

And programs are synchronized compiler could not

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Unformatted text preview: zed (GOOD PROGRAMS!) – Models characterized by their attitude towards: RAR, WAR, RAW, WAW to different addresses ff 52 Relaxed Consistency Models: The Basics • Key idea: allow reads and writes to complete out of order, but use synchronization operations to enforce ordering a synchronized program behaves as if the processor were if th sequentially consistent – By relaxing orderings, may obtain performance advantages – Also specifies range of legal compiler optimizations on shared data – Unless synchronization points are clearly defined and programs are synchronized, compiler could not interchange read and write of 2 shared data items because might affect the semantics of the program • 3 major sets of relaxed orderings: 1. W→R ordering (all writes completed before next read) (all writes completed before next read) • Retains ordering among writes many programs that operate under sequential consistency operate under this model, without additional synchronization. Called processor consistency 2. W → W ordering (all writes completed before next write) (all writes completed before next write) 3. R → W & R → R orderings, a variety of models depending on ordering restrict...
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