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CS294-6Reconfigurable Computing
Day 9
September 22, 1998
Project Startup: Mediabench
With annotations from class discussion
Today
• Project– Goals– Tuning (get feedback from class)– Benchmark set– …more architecture/compute model context
Pedagogical Goal
• Give students an appreciation for tradeoffs designing “post-fabrication” programmable computing devices– focus on spatial architectures
• benefits
• design
High level things want to see
• Where spatial computing better than processor? – Worse?
• How optimize a design for spatial execution? – What’s different about?
• How tune/optimize spatial architecture?
What do you want?
• What are your most burning, unanswered questions in this area?– What should we try to answer?– What would you like to learn?
Burning Questions
• Real numbers for compute array versus processor– larger than Day 5 examples– computational density– energy/op
• How exploit real-time reconfiguration– swapping efficiently– spatio/temporal tradeoffs– virtualization (decompose, run-time manage)
Burning Questions
• Design memory for embedding with array– size
• distribution
• memory hierarchy
– interconnect to– interfacing
• physical
• control
Burning Questions
• Good automatic compilation possible?– How describe
• ease mapping
• ease user job
• Costs and overheads to– upgradability– portability
Burning Questions
• What’s wrong w/ fixed length (processor) word model?– Architecturally– description– work knowledge of data size req. into
specification– annotations
• requested by compiler?
Burning Questions
• How should P<=>FPGA talk to each other– change ISA?– How does presence of RC change workload
(requirements) for processor?
• Beneficial use RC as GP platform?– How attack?
• Computational model?
Burning Questions
• Homogenous/Heterogeneous architecture?
• Generation n+1 mainstream processor?
• Minimum array size to be useful?– Embedded cost sensitivity– general: benefit vs. array size
Burning Questions
• Applications– make new things viable which are not viable
today?• ? Anything other than putting 10x 100x computation
in affordable package?
– Building a better mousetrap isn’t enough?• Lag to exploit technology?
• Low on innovation side?
Burning Questions
• System-on-a-chip designs?– Design complexity (up)– IP – …surely do something innovative with (?)– place for spatial building blocks
AMD (Benefit)
• Where beneficial? – (expand day 5 comparisons)
• Power implications– Spatial have benefit?– When/where?
AMD (How Use)
• Area Time tradeoffs– What look like?– How achieve?– Importance?
• Specialization– What opportunities exist?– Importance of exploiting?– How exploit?
AMD (How Use)
• How do we build programs? Including:– Convenience?– Abstraction?– Application longevity?– Virtualization
AMD (Architecture)
• How compute (media apps) requirements differ from random logic?– Interconnect
• less? More stylized?
– Retiming• depth, heirarchy?
Original Plan
• mediabench kernels
• start with HSRA architecture and tools
• series of weekly projects– (to be tuned based on student feedback and
areas of interest)
• final writeup
Original Plan: Exercises
• Analyze sequential implementation
• Build spatial (HSRA) implementation– compare yielded density w/ sequential
• Model power– compare spatial/sequential
Original Plan: Exercises
• Interconnect– c,p for application– “right” amount of interconnect– non-Rent structure in application interconnect?– Quality of hand autoplacement ?– ??? Heirarchical vs mesh style ???
Original Plan
• Retiming– depth distribution– hierarchy
• when use memories, what sizes?
– ?? Output vs. input ??
Original Plan: Exercises
• Specialization– opportunities in your application– binding times– benefits
• Programming– How fit into stream model of full computation?– Scheduling/virtualization?
Benchmark Set
• No need to hype multimedia as computational driver?
• See many “band-aids” on conventional architectures to handle – MMX, VIS
• Desire for “programmable” solutions– multi/evolving standards– one device does it all
Benchmarks
• Audio– adpcm
– g.721
– gsm
• Still Image– epic
– JPEG
• Video– MPEG-2
• Encryption– pegwit
– pgp
• Rendering– mesa
– ghostscript(?)
• Speech Recognition– rasta
Hypothesis
• Spatial processing a better solution than “tweaking” ISAs– broader applicability– greater computational density– lower power
• Special-Purpose processing units brittle– e.g. FIR