MCS-284 Homework 1 (Fall 1999)
Due: September 15, 1999
From the data on page 73, how much higher is the CPI of the 200 MHz
Pentium system than the CPI of the 100 MHz Pentium system on the
SPECint95 workload? On the SPECfp95 workload? (Ignore the issue that
each SPEC ratio is actually a geometric mean over different programs;
pretend that a single int workload and a single fp workload is
represented.) Be sure to use the numerical data given in the text
rather than trying to estimate the numbers from the graph. You'll get
more precise results that way.
Do exercises 2.31-2.32 on page 96.
You are the manager of a microprocessor design team. Your
microprocessor currently has an average CPI of 1.5. The software that
will run on your microprocessor already exists and is fixed: it will
not be rewritten or recompiled in response to your design decisions.
One of the members of your design team suggests a change that will
reduce the CPI of multiply instructions from 3 to 2 (and leave the CPI
of other instructions unchanged). However, it will require
lengthening the cycle time by 5%. You need to decide whether this
change is desirable or not.
Note that if the software makes no use of multiply instructions, the
change will be a bad idea, since the cycle time will be increased
without any decrease in the number of cycles. Conversely, if the
software is nothing but multiply instructions, the change will be a
good idea, since one third of the cycles will be eliminated, which
will more than pay for a 5% increase in cycle time.
Real software is presumably somewhere in between these two extremes.
What fraction of the instructions executed need to be multiplies for
the proposed change to be a good one?
Instructor: Max Hailperin