Consider a memory with ability to loadstore to memory

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Unformatted text preview: re to memory. We can think of that memory as files, as objects in an RMI system, as DRAM, as disk in a network attached disk. Same issue in each case. Example 1: CPU0: v0 = f0(); done0 = true; CPU1: while(done0 == false) ; v1 = f1(v0); done1 = true; CPU2: while(done1 == false) ; v2 = f2(v0, v1); Intuitive intent: CPU2 should execute f2() with results from CPU0 and CPU1 waiting for CPU1 implies waiting for CPU0 Problem A: CPU0's writes of v0 and done0 may be interchanged by network leaving v0 unset but done0=true (Q: suppose we implement the memory by sending updates to every node. Would your RPC design have this problem? That is, can a later RPC be processed before an earlier one?) Can fix this if each CPU sees each other's writes in issue order. Not always a good assumption. For performance, most CPUs issue multiple read/write operations in parallel, without waiting for the previous one to complete (hide high latency operations). For writes, issue them in order, but if they go to different memory banks (aka shards of a database), may complete (be visible to other processors) in a different orde...
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This document was uploaded on 04/04/2014.

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