A novel cache architecture to support layerfour packet classification at memory access speeds

1
A novel cache architecture to support layer-four
packet classification at memory access speeds

• Jun Xu Singhal, M. Degroat, J.
• INFOCOM 2000

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Outline

• Approach
• Architecture
• Near-LRU
• Static Set-Associative Scheme
• Cache Replacement
• Dynamic Set-Associative Scheme
• Lazy-Writeback

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Architecture
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Static Set-Associative Scheme
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Cache Replacement

• The replacement logic is to search the
  corresponding cache entries in bank I1, I2,
  ..., and IN (modulo N) in sequence, and the
  first one that expires will the replaced.
• If no banks expire, the item in bank I1 will be
  replaced.

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Expire

• The timestamps field consists of an 8-bit
  timestamp LIFESPAN that records when the entry
  was created, and an 8-bit timestamp EXPIRE that
  records when the entry was last updated.
• LIFESPAN is used to check whether the entry is
  more than Dlifespon seconds old, which indicates
  that the cache entry should no longer be trusted.
• EXPIRE is used to check whether the entry has
  expired.

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Dynamic Set-Associative Scheme (1)

• Static set-associative cache will bring about a
  high volume of collision miss when its load is
  high.
• We cut the collision miss using universal hash
  function.
• These N hash functions h1, h2, . - . , hN satisfy
  the following property. Given a random hash key X
  , h1 (X), h2 (X),.. -,and hN ( X) are identical
  independent uniformly distributed random
  variables.

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Dynamic Set-Associative Scheme (2)
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Lazy-Writeback

• For a series of packets hit a entry, there is
  really no need to perform a writeback every time.
  
• When a hit happens, there will be a writeback
  only if the entry is more than Dwriteback seconds
  old.