•S3MP’s
cache coherency protocol implements strong consistency
–Many
recent designs implement a weaker consistency model…
•S3MP
uses a singly-linked sharing chain
–Widely-shared
data – long chains – long invalidations, nasty replacements
–“Widely
shared data is rare”
•In
real life:
–IEEE
Scalable Coherent Interconnect (SCI): doubly-linked sharing list
–SGI
Origin 2000: bit vector sharing list
•Real
Origin 2000 systems in service with 256 CPUs
–Sun
E10000: hybrid multiple buses for invalidations, separate switched network for data transfers
•Many
E10000s in service, often with 64 CPUs