[15/20/15/15]The difference between peak and sustained performance
can be large. For one problem, a Hitachi S810 had a peak speed twice as
high as that of the Cray X-MP, while for another more realistic problem, the Cray
X-MP was twice as fast as the Hitachi processor. Let’s examine why this might
occur using two versions of VMIPS and the following code sequences:
C Code sequence 1
do 10 i=1,10000
A(i)=x * A(i)+y * A(i)
10 continue
C Code sequence 2
do 10 i=1,100
A(i)=x * A(i)
10 continue
Assume there is a version ofVMIPS (call itVMIPS-II) that has two copies of every
floating-point functional unit with full chaining among them. Assume that both
VMIPS and VMIPS-II have two load-store units. Because of the extra functional
units and the increased complexity of assigning operations to units, all the overheads
(Tloop and Tstart) are doubled for VMIPS-II.
a. [15]Find the number of clock cycles on code sequence 1
on VMIPS.
b. [20]Find the number of clock cycles on code sequence 1 for
VMIPS-II. How does this compare to VMIPS?
c. [15]Find the number of clock cycles on code sequence 2 forVMIPS.
d. [15]Find the number of clock cycles on code sequence 2 for
VMIPS-II. How does this compare to VMIPS?