Appendix E Mathematics Of Prefetch Scheduling Distance; Simplified Equation - Intel ARCHITECTURE IA-32 Reference Manual

Mathematics of Prefetch
Scheduling Distance
This appendix discusses how far away to insert prefetch instructions. It
presents a mathematical model allowing you to deduce a simplified
equation which you can use for determining the prefetch scheduling
distance (PSD) for your application.
For your convenience, the first section presents this simplified equation;
the second section provides the background for this equation: the
mathematical model of the calculation.

Simplified Equation

A simplified equation to compute PSD is as follows:
=
psd
where
psd
Nlookup
Nxfer
and
N
pref
CPI
+
Nlookup Nxfer
------------------------------------------------------------------------------ -
CPI N
is prefetch scheduling distance.
is the number of clocks for lookup latency. This
parameter is system-dependent. The type of memory
used and the chipset implementation affect its value.
is the number of clocks to transfer a cache-line. This
parameter is implementation-dependent.
are the numbers of cache lines to be prefetched and
N
st
stored.
is the number of clocks per instruction. This parameter
is implementation-dependent.
⋅ (
+
N N
pref st
⋅
inst
)
E
E-1