ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

Cache contention
Is when the number of frequently-used memory cache lines that use a particular cache set exceeds the
set-associativity of the cache. In this case, main memory activity goes up and performance drops.
Glossary
Cache hit
Is a memory access that can be processed at high speed because the data it addresses is already in the cache.
Cache line
Is the basic unit of storage in a cache. Its size is always a power of two (usually 4 or 8 words), and must be
aligned to a suitable memory boundary. A memory cache line is a block of memory locations with the same
size and alignment as a cache line. Memory cache lines are sometimes loosely just called cache lines.
Cache line index
Is a number associated with each cache line in a cache set. In each cache set, the cache lines are numbered
from 0 to (set associativity)–1.
Cache lockdown
Alleviates the delays caused by accessing a cache in a worst-case situation. Cache lockdown enables critical
code and data to be loaded into the cache so that the cache lines containing them are not subsequently
re-allocated. This ensures that all subsequent accesses to the code and data concerned are cache hits and so
complete quickly.
Cache lockdown blocks
Consist of one line from each cache set. Cache lockdown is performed in units of a cache lockdown block.
Cache miss
Is a memory access that cannot be processed at high speed because the data it addresses is not in the cache.
Cache sets
Are areas of a cache, divided up to simplify and speed up the process of determining whether a cache hit
occurs. The number of cache sets is always a power of two.
Cache way
A cache way consists of one cache line from each cache set. The cache ways are indexed from 0 to
ASSOCIATIVITY-1. The cache lines in a cache way are chosen to have the same index as the cache way.
So for example cache way 0 consists of the cache line with index 0 from each cache set, and cache way n
consists of the cache line with index n from each cache set.
Callee-save registers
Are registers that a called procedure must preserve. To preserve a callee-save register, the called procedure
would normally either not use the register at all, or store the register to the stack during procedure entry and
re-load it from the stack during procedure exit.
Caller-save registers
Are registers that a called procedure need not preserve. If the calling procedure requires their values to be
preserved, it must store and reload them itself.
Condition field
Is a 4-bit field in an instruction that is used to specify a condition under which the instruction can execute.
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