Intel Itanium 9150M, Manual, Page: 154 / 420

Volume 3: Instruction Reference 3:145
hint
hint — Performance Hint
Format: (
qp
) hint
imm
21
pseudo-op
( qp ) hint.i
imm
21
i_unit_form I18
( qp ) hint.b
imm
21
b_unit_form B9
( qp ) hint.m
imm
21
m_unit_form M48
( qp ) hint.f
imm
21
f_unit_form F16
( qp ) hint.x
imm
62
x_unit_form X5
Description:
Provides a performance hint to the processor about the program being executed. It has
no effect on architectural machine state, and operates as a
nop
instruction except for its
performance effects.
The immediate,
imm
21
or
imm
62
, specifies the hint. For the x_unit_form, the L slot of the
bundle contains the upper 41 bits of
imm
62
.
This instruction has five forms, each of which can be executed only on a particular
execution unit type. The pseudo-op can be used if the unit type to execute on is
unimportant.
Operation: if (PR[ qp ]) {
if (x_unit_form)
hint = imm
62
;
else // i_unit_form || b_unit_form || b_unit_form || f_unit_form
hint = imm
21
;
if (is_supported_hint(hint))
execute_hint(hint);
}
Interruptions:
None
Table 2-31. Hint Immediates
imm
21
or imm
62
Mnemonic Hint
0x0 @pause Indicates to the processor that the currently executing stream is waiting,
spinning, or performing low priority tasks. This hint can be used by the
processor to allocate more resources or time to another executing stream
on the same processor. For the case where the currently executing stream
is spinning or otherwise waiting for a particular address in memory to
change, an advanced load to that address should be done before
executing a
hint @pause
; this hint can be used by the processor to
resume normal allocation of resources or time to the currently executing
stream at the point when some other stream stores to that address.
0x1 @priority Indicates to the processor that the currently executing stream is performing
a high priority task. This hint can be used by the processor to allocate more
resources or time to this stream. Implementations will ensure that such
increased allocation is only temporary, and that repeated use of this hint
will not impair longer-term fairness of allocation.
0x02-0x3f These values are available for future architected extensions and will
execute as a
nop
on all current processors. Use of these values may
cause unexpected performance issues on future processors and should
not be used.
other Implementation specific. Performs an implementation-specific hint action.
Consult processor model-specific documentation for details.