Unreliable Silicon: Myth or Reality?

1
Unreliable Silicon Myth or Reality?

• Shubu Mukherjee
• Principal Engineer
• Director, SPEARS Group
• (SPEARS Simulation Pathfinding of Efficient
  And Reliable Systems)
• Intel Corporation
• Workshop on Computer Architecture Research
  Directions (CARD)
• Feb. 11th, 2007

2
Whats the Truth?

• There are three versions of the truth
• My truth
• Your truth
• The truth

3
The Truth Silicon is Becoming Unreliable
4
The End-Users Truth

• End-users
• Care deeply about reliable systems
• May not be able to determine why their system
  failed
• Expect the industry to produce reliable systems
  for them
• Goal of silicon vendors
• Keep silicon errors low enough (e.g., lt 0.1 of
  all errors)
• Low enough that end-users dont notice or dont
  care
• Point Risks
• Individual corruption or crash may be critical
  (e.g., Windows 98 crash during a Gates demo)
• End-users may demand chip replacement, even if
  the error was not permanent

5
The IT Manager or Vendors Truth

• The Lightbulb Phenomenon
• A house with 48 lightbulbs, each with 4 year MTTF
• Will replace a lightbulb every month
• Negative Impact to Business ? billions of dollars
  involved
• Increased total cost of ownership
• Product returns replacement
• Loss of data and/or availability

6
The Designers Awakening

• Shock
• SER is the crabgrass in the lawn of computer
  design
• Denial
• We will do the SER work two months before
  tapeout
• Anger
• Our reliability target is too ambitious
• Acceptance
• You can deny physics only for so long

Designers have accepted silicon reliability as a
challenge they will have to deal with
7
The Designers Challenge

• Protection comes from
• Process improved process technology
• Materials shielding for alpha particles
• Circuits rad-hard cells
• Architecture ECC, parity, hardened gates,
  redundant execution
• Software can provide detection recovery at
  higher level
• Companies constantly making trade-offs for
  reliability
• Cost of protection (performance die size) vs.
  chip reliability
• Products must meet the end-users reliability
  expectations

Industry will produce reliably operating parts
8
Industry Needs Help with Research

• Academia has some misconceptions
• MTBF is only a rough estimate of an individual
  parts life
• A system hang does not protect from data
  corruption
• Adding protection without correction does not
  reduce the overall error rate
• Research needed in different areas of silicon
  reliability
• How do we predict and/or measure error rate from
  radiation, wearout, variability?
• How do we detect soft errors, wearout,
  variability on individual parts?
• Many traditional solutions exist, but how do we
  make them cheaper?