Multicast snooping: a new coherence method using a multicast address network

This paper proposes a new coherence method called "multicast snooping" that dynamically adapts between broadcast snooping and a directory protocol. Multicast snooping is unique because processors predict which caches should snoop each coherence transaction by specifying a multicast "m...

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Bibliographic Details
Published in:	Proceedings of the 26th International Symposium on Computer Architecture (Cat. No.99CB36367) pp. 294 - 304
Main Authors:	Bilir, E.E., Dickson, R.M., Ying Hu, Plakal, M., Sorin, D.J., Hill, M.D., Wood, D.A.
Format:	Conference Proceeding
Language:	English
Published:	IEEE 1999
Subjects:	Bandwidth Broadcasting Coherence Computational modeling Microprocessors Power transmission lines Protocols Sun Timing
Online Access:	Get full text
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Summary:	This paper proposes a new coherence method called "multicast snooping" that dynamically adapts between broadcast snooping and a directory protocol. Multicast snooping is unique because processors predict which caches should snoop each coherence transaction by specifying a multicast "mask". Transactions are delivered with an ordered multicast network, such as an Isotach network, which eliminates the need for acknowledgment messages. Processors handle transactions as they would with a snooping protocol while a simplified directory operates in parallel to check masks and gracefully handle incorrect ones (e.g., previous owner missing). Preliminary performance numbers with mostly SPLASH-2 benchmarks running on 32 processors show that we can limit multicasts to an average of 2-6 destinations (/spl Lt/ 32) and we can deliver 2-5 multicasts per network cycle (/spl Gt/ broadcast snooping's 1 per cycle). While these results do not include timing, they do provide encouragement that multicast snooping can obtain data directly (like broadcast snooping) but apply to larger systems (like directories).
ISBN:	0769501702 9780769501703
ISSN:	1063-6897 2575-713X
DOI:	10.1109/ISCA.1999.765959