Intel ARCHITECTURE IA-32, Reference Manual, Page: 559 / 568

Mathematics of Prefetch Scheduling Distance
E
E-13
In reality, the front-side bus (FSB) pipelining depth is limited, that is,
only four transactions are allowed at a time in the Pentium
III and
Pentium 4 processors. Hence a transaction bubble or gap, T
g
, (gap due
to idle bus of imperfect front side bus pipelining) will be observed on
FSB activities. This leads to consideration of the transaction gap in
computing the prefetch scheduling distance. The transaction gap,
T
g
,
must be factored into the burst cycles, T
b
, for the calculation of prefetch
scheduling distance.
The following relationship shows computation of the transaction gap.
where T
l
is the memory leadoff latency, c is the number of chunks per
cache line and n is the FSB pipelining depth.
Figure E-7 Accesses per Iteration, Example 2
0
1
2
3
4
5
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45
Tc (in FSB clocks)
ps
d
2 lines
4 lines
6 lines
psd for different number of cache lines prefetched per iteration