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Data Prefetching
Intel Core Solo and Intel Core Duo processors provide hardware
mechanisms to prefetch data from memory to the second-level cache.
There are two techniques: one mechanism activates after the data access
pattern experiences two cache-reference misses within a trigger-distance
threshold (see Table 1-2). This mechanism is similar to that of the
Pentium M processor, but can track 16 forward data streams and 4
backward streams. The second mechanism fetches an adjacent cache
line of data after experiencing a cache miss. This effectively simulates
the prefetching capabilities of 128-byte sectors (similar to the sectoring
of two adjacent 64-byte cache lines available in Pentium 4 processors).
Hardware prefetch requests are queued up in the bus system at lower
priority than normal cache-miss requests. If bus queue is in high
demand, hardware prefetch requests may be ignored or cancelled to
service bus traffic required by demand cache-misses and other bus
transactions.
Hardware prefetch mechanisms are enhanced over that of Pentium M
processor by:
•
Data stores that are not in the second-level cache generate read for
ownership requests. These requests are treated as loads and can
trigger a prefetch stream.
•
Software prefetch instructions are treated as loads, they can also
trigger a prefetch stream.
Hyper-Threading Technology
®
Intel
Hyper-Threading (HT) Technology is supported by specific
members of the Intel Pentium 4 and Xeon processor families. The
technology enables software to take advantage of task-level, or
thread-level parallelism by providing multiple logical processors within
a physical processor package. In its first implementation in Intel Xeon
processor, Hyper-Threading Technology makes a single physical
processor appear as two logical processors.
IA-32 Intel® Architecture Processor Family Overview
1-33
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