A Novel Cache Architecture and Placement Framework for Packet Forwarding Engines

Packet forwarding is a memory-intensive application requiring

multiple accesses through a trie structure. With the requirement to process

packets at line rates, high performance routers need to forward millions of

packets every second with each packet needing up to 7 memory accesses.

Earlier work shows that a single cache for the nodes of a trie can reduce

the number of external memory accesses.

It is observed that the locality characteristics of the level-one nodes of

a trie are significantly different from those of lower-level nodes. Hence,

we propose a heterogeneously segmented cache architecture (HSCA) which

uses separate caches for level-one and lower-level nodes each with carefully

chosen sizes. Besides reducing misses, segmenting the cache allows us to

focus on optimizing the more frequently accessed level-one node segment.

We find that due to the non uniform distribution of nodes among cache

sets, the level one nodes cache is susceptible to high conflict misses. We

reduce conflict misses by introducing a novel two-level mapping based

cache placement framework. We also propose an elegant way to fit the

modified placement function into the cache organization with minimal

increase in access time. Further, we propose an attribute preserving trace

generation methodology which emulates real traces and can generate traces

with varying locality. Performance results reveal that our HSCA scheme

results in a 32% speedup in average memory access time over a unified

nodes cache. Also, HSCA outperforms IHARC, a cache for lookup results,

with as high as a 10 fold speedup in average memory access time. Twolevel

mapping further enhances the performance of the base HSCA by up

to 13% leading to an overall improvement of up to 40% over the unified

scheme.

In  IEEE Transactions on Computers (IEEE TC)

Publisher  Institute of Electrical and Electronics Engineers, Inc.
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