penn ese534 spring2012 -- dehon 1 ese534 computer organization day 19: march 28, 2012 minimizing...
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Penn ESE534 Spring DeHon 3 At Issue Many now argue energy will be the ultimate scaling limit –(not lithography, costs, …) Proliferation of portable and handheld devices –…battery size and life biggest issues Cooling, energy costs may dominate cost of electronics –Even server room applicationsTRANSCRIPT
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Penn ESE534 Spring2012 -- DeHon1
ESE534Computer Organization
Day 19: March 28, 2012Minimizing Energy
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Penn ESE534 Spring2012 -- DeHon2
Today
• Discuss broad set of architectural options to reduce energy
• Relevant to upcoming project
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Penn ESE534 Spring2012 -- DeHon3
At Issue• Many now argue energy will be the
ultimate scaling limit– (not lithography, costs, …)
• Proliferation of portable and handheld devices– …battery size and life biggest issues
• Cooling, energy costs may dominate cost of electronics – Even server room applications
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Microprocessor Power Density
Penn ESE534 Spring2012 -- DeHon4
The Future of Computing Performance: Game Over or Next Level?National Academy Press, 2011
http://www.nap.edu/catalog.php?record_id=12980
Watts
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Penn ESE534 Spring2012 -- DeHon Source: Carter/Intel 5
Power Limits Integration
Impact
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Watch
• Energy optimized along with area, delay• Energy optimized with little or no effect
on area/delay• Energy trades off with area, delay
Penn ESE534 Spring2012 -- DeHon6
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Penn ESE534 Spring2012 -- DeHon7
Energy
€
E =12
aiCiVi2 ⎛
⎝ ⎜ ⎞ ⎠ ⎟
i∑
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Penn ESE534 Spring2012 -- DeHon8
Energy
€
E =12
aiCiVi2 ⎛
⎝ ⎜ ⎞ ⎠ ⎟
i∑
How scale down V?
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Penn ESE534 Spring2012 -- DeHon9
Energy and Delay
2
21 CVE
gd=Q/I=(CV)/I
Id,sat=(COX/2)(W/L)(Vgs-VTH)2
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Penn ESE534 Spring2012 -- DeHon10
Energy/Delay Tradeoff
• EV2
• gd1/V
• We can trade speed for energy• E×(gd)2 constant
Martin et al. Power-Aware Computing, Kluwer 2001 http://caltechcstr.library.caltech.edu/308/
2
21 CVE
gd=(CV)/IId,sat (Vgs-VTH)2
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Penn ESE534 Spring2012 -- DeHon11
Area/Time Tradeoff• Also have Area-Time tradeoffs
– HW2 spatial vs temporal multipliers– See more next week
• Compensate slowdown with additional parallelism
• …trade Area for Energy Architectural Option– HW3.3
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Reduce V
• Lower voltage and run in parallel– HW3.3
• Lower voltage when you can get away with it (as much as can get away with)– Dynamic Voltage Scaling
• Lower voltage where don’t need it– Multiple Vdd
Penn ESE534 Spring2012 -- DeHon12
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Penn ESE534 Spring2012 -- DeHon13
Energy
€
E =12
aiCiVi2 ⎛
⎝ ⎜ ⎞ ⎠ ⎟
i∑
How reduce C?
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Reduce C• Shallow memory banks• Reduce overhead programmable
– Switches/stubs• Reduce wire lengths
– Maybe from reducing area• Size gates • Exploit technology• Specialize computation or compute element
Penn ESE534 Spring2012 -- DeHon14
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Penn ESE534 Spring2012 -- DeHon15
Energy
€
E =12
aiCiVi2 ⎛
⎝ ⎜ ⎞ ⎠ ⎟
i∑
How reduce a?
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Reduce a• Avoid/reduce glitches• Code data
– Example FSM– Example data encoding– Example bus-invert– One hot
• Compress data (send less)• Exploit correlations• Power Gate unused regions
Penn ESE534 Spring2012 -- DeHon16
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Penn ESE534 Spring2012 -- DeHon17
Energy
€
E =12
aiCiVi2 ⎛
⎝ ⎜ ⎞ ⎠ ⎟
i∑
How reduce CV2?
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Reduce CV coupling
• Low swing highly capacitive signals– Bit-lines– Interconnect?
Penn ESE534 Spring2012 -- DeHon18
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Penn ESE534 Spring2012 -- DeHon19
Energy
€
E =12
aiCiVi2 ⎛
⎝ ⎜ ⎞ ⎠ ⎟
i∑
How reduce aC?
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Reduce aC
• Put high a with low C• Coding/compression at high C points
Penn ESE534 Spring2012 -- DeHon20
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Total Energy
• Etotal = Eswitch+Eleak
Penn ESE534 Spring2012 -- DeHon21
€
E =12
aiCiVi2 ⎛
⎝ ⎜ ⎞ ⎠ ⎟
i∑
€
E leak = Tcycle × V × Ileak
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Total Energy
• Etotal = Eswitch+Eleak
Penn ESE534 Spring2012 -- DeHon22€
E =12
aiCiVi2 ⎛
⎝ ⎜ ⎞ ⎠ ⎟
i∑
€
E leak = Tcycle × V × Ileak
What if ai is small? Tcycle large?
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Graph for In Class (Day 6)
Penn ESE534 Spring2012 -- Mehta & DeHon23
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Leakage
Penn ESE534 Spring2012 -- DeHon24
€
E leak = Tcycle × V × Ileak
How reduce Tcycle?
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Reduce Tcycle
• Run as fast as can• Optimize for delay• Pipeline
Penn ESE534 Spring2012 -- DeHon25
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Leakage
Penn ESE534 Spring2012 -- DeHon26
€
E leak = Tcycle × V × Ileak
How reduce V?
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Reduce V?
• Power gate power down when not in use
Penn ESE534 Spring2012 -- DeHon27
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Leakage
Penn ESE534 Spring2012 -- DeHon28
€
E leak = Tcycle × V × Ileak
How reduce Ileak?
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Reduce Leakage Current
• Power gating• Increase Vth
Penn ESE534 Spring2012 -- DeHon29
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Admin
• HW9 – note parts to run on computer– Don’t wait until Sunday to run them
• Reading for Monday on web
Penn ESE534 Spring2012 -- DeHon30
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Penn ESE534 Spring2012 -- DeHon31
Big Ideas• Power major limiter going forward
– Can put more transistors on a chip than can switch
• Some optimizations good for energy as well as (area, delay)
• Some optimizations just for energy– No effect on area, delay
• Changes tradeoffs will make