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Microarchitecture is Dead AND We must have a multicore interface that does not require programmers to understand what is going on underneath.

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Presentation on theme: "Microarchitecture is Dead AND We must have a multicore interface that does not require programmers to understand what is going on underneath."— Presentation transcript:

1 Microarchitecture is Dead AND We must have a multicore interface that does not require programmers to understand what is going on underneath

2 What is Microarchitecture? It is about the implementation It is transparent to the software Ergo, if we really want to protect the programmer from seriously understanding the multi-core chip, Microarchitecture must be very much alive and well

3 First, a few words about the multi-core chip: The following figure was first published in a UT Tech Report: “ACMP: Balancing Hardware Efficiency and Programmer Efficiency,” TR-HPS , Feb, 2007 (Actually, it was first submitted to ISCA in June, 2006, and was rejected  )

4 The Asymmetric Chip Multiprocessor (ACMP) Niagara -like core Large core ACMP Approach Niagara -like core “Niagara” Approach Large core Large core Large core “Tile-Large” Approach

5 Large core vs. Small Core Out-of-order Wide fetch e.g. 4-wide Deeper pipeline Aggressive branch predictor (e.g. hybrid)‏ Many functional units Trace cache Memory dependence speculation In-order Narrow Fetch e.g. 2-wide Shallow pipeline Simple branch predictor (e.g. Gshare)‏ Few functional units Large Core Small Core

6 Throughput vs. Serial Performance

7 To make that chip viable, a lot has to happen: The interconnect among the cores The shared resources –Caches (and cache coherence) –Memory Controller(s) –Prefetch mechanisms Specification of the few heavyweight cores and the many mickey-mouse cores Performance improvement of the heavyweight core Specification of accelerators and their interconnect to the cores Specification of the interface to the software (ISA)

8 Actually, I don’t believe the Microarchitecture can do it alone BUT that does not reduce the importance of the microarchitecture Everything on the previous slide will be needed PLUS at least two interfaces: –One for users who can understand the hardware, and –One for the run-time system to smooth the way for users who do not understand the hardware That will mean breaking the transformation hierarchy

9 Algorithm Program ISA (Instruction Set Arch) Microarchitecture Circuits Problem Electrons

10 and that means (in my view) A vibrant future for Microarchitecture


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