Locality Hints Specified By Each Instruction Class - Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual

Figure 4-1.
Register
Files
The temporal structures cache memory accessed with temporal locality; the
non-temporal structures cache memory accessed without temporal locality. Both
structures assume that memory accesses possess spatial locality. The existence of
separate temporal and non-temporal structures, as well as the number of levels of
cache, is implementation dependent. Please see the processor-specific documentation
for further information.
Three mechanisms are defined for allocation control: locality hints; explicit prefetch;
and implicit prefetch. Locality hints are specified by load, store, and explicit prefetch
(lfetch) instructions. A locality hint specifies a hierarchy level (e.g., 1, 2, all). An
access that is temporal with respect to a given hierarchy level is treated as temporal
with respect to all lower (higher numbered) levels. An access that is non-temporal with
respect to a given hierarchy level is treated as temporal with respect to all lower levels.
Finding a cache line closer in the hierarchy than specified in the hint does not demote
the line. This enables the precise management of lines using lfetch and then
subsequent uses by.nta loads and stores to retain that level in the hierarchy. For
example, specifying the.nt2 hint by a prefetch indicates that the data should be cached
at level 3. Subsequent loads and stores can specify.nta and have the data remain at
level 3.
Locality hints do not affect the functional behavior of the program and may be ignored
by the implementation. The locality hints available to loads, stores, and explicit prefetch
instructions are given in
both temporal and spatial locality with respect to level 1.
Table 4-18. Locality Hints Specified by Each Instruction Class
Mnemonic
none
nt1
nt2
nta
1:70
Memory Hierarchy
Level 1 Level 2
Temporal Temporal
Structure Structure
Non- Non-
temporal temporal
Structure Structure
Table 4-18. Instruction accesses are considered to possess
Locality Hint
Temporal, level 1
Non-temporal, level 1
Non-temporal, level 2
Non-temporal, all levels
Level N
Temporal
Structure
temporal
Structure
Cache
Instruction Type
Load
x
x
x
Volume 1, Part 1: Application Programming Model
Memory
Non-
lfetch,
Store
lfetch.fault
x x
x
x
x x