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토큰 코히런스 프로토콜을 위한 경서열 트렌지언트 요청 처리 방법
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- Issue Date
- 2005-10
- Citation
- 전기학회논문지 D : 시스템 및 제어부문, v.54D, no.10, pp.615-619
- ISSN
- 1229-6287
- Publisher
- 대한전기학회 (KIEE)
- Language
- Korean
- Type
- Journal Article
- Abstract
- Token coherence protocol has many good reasons against snooping/directory-based protocol in terms of latency, bandwidth, and complexity. Token counting easily maintains correctness of the protocol without global ordering of request, which is basis of other dominant cache coherence protocols. But this lack of global ordering causes starvation which is not happening in snooping/directory-based protocols. Token coherence protocol solves this problem by providing an emergency mechanism called persistent request. It enforces other processors in the competition for accessing same shared memory block, to give up their tokens to feed a starving processor. However, as the number of processors grows in a system, the frequency of starvation occurrence increases. In other words, the situation where persistent request occurs becomes too frequent to be emergent. As the frequency of persistent requests increases, not only the cost of each persistent matters since it is based on broadcasting to all processors, but also the increased traffic of persistent requests will saturate the bandwidth of multiprocessor interconnection network. This paper proposes a new request mechanism that defines order of requests to reduce occurrence of persistent requests. This ordering mechanism has been designed to be decentralized since centralized mechanism in both snooping-based protocol and directory-based protocol is one of primary reasons why token coherence protocol has advantage in terms of latency and bandwidth against these two dominant protocols.
- KSP Keywords
- Cache coherence protocols, Directory-based, Interconnection Network, Multiprocessor interconnection, Shared Memory, number of processors