QG5000XSL9TH Datasheet, PDF (301/458 Pages) Intel Corporation – Intel 5000X Chipset Memory Controller Hub (MCH)

Functional Description
5.2
Snoop Filter
The Snoop Filter (SF) offers significant performance enhancements on several
workstation benchmarks by eliminating traffic on the snooped frontside bus of the
processor being snooped. By removing snoops from the snooped bus, the full
bandwidth is available for other transactions. Supporting concurrent snoops effectively
reduces performance degradation attributable to multiple snoop stalls. See Figure 5-1,
“Snoop Filter” on page 302.
The SF is composed of two affinity groups each containing 8K sets of x16-way
associative entries. The overall SF size is 16MB in size. Each affinity group supports a
pseudo-LRU replacement algorithm. Lookups are done on a full 32-way per set for hit/
miss checks.
As shown in Figure 5-1 the snoop filter is organized in two halves referred to as the
Affinity Group 1 and Affinity Group 0 or the odd and even snoop filters respectively. As
shown in Figure 5-1 Affinity Group 1 is associated with processor 1 and Affinity Group 0
is associated with processor 0. Under normal conditions a snoop is competed with a 1
snoop stall penalty. When the processors request simultaneous snoops the first snoop
is completed with a one snoop stall penalty, the second snoop requires a 2 snoop stall
penalty.
For the purposes of simultaneous SF access arbitration, processor 0 is given priority
over processor 1. Thus simultaneous snoops are resolved with a 1 snoop stall penalty
for processor 0 and a 2 snoop stall penalty for processor 2.
Intel^® 5000X Chipset Memory Controller Hub (MCH) Datasheet
301