# Quiz3 GC ans

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```					Quiz 3, Feb 2, 2011
CSE 591 Topics in Green Computing and Communication, Spring 2011
Time: 10min Points: 10

1. (1 pt) If a datacenter pays \$ A for each amp usage per year, what would be the total annual
electricity bill for using N severs consuming W watts each. Assume V Volts power supply and PDUs
have E% efficiency.

A(NW)/EV

2. ( 1 pt)Assume an N core chip and suppose we can Turbo Boost one core X times. For a given
computation what speedup you can get if you can use all N cores (parallel execution) without Turbo
Boosting as opposed to Turbo boosted single core performance (turbo boosted sequential
performance).

N/X

3. (2 pt)Now suppose the application has s% sequential code (which can be turbo boosted) and parallel
part can utilize all N cores (with no turbo boosting). What speedup (against non-parallelized non-
turbo boosted code) can be obtained for this application?

XN/(sN + X(1-s))

4. (2 pt)Suppose for three runs of an optimized code we get speedups of 2, 12, and 1/3, respectively.
What is the arithmetic mean and what is the geometric mean of the speedups?

AM = (2+12+1/3)/3 ; GM = (2*12*1/3)^(1/3)

5. (1 pt)What is the difference between “balanced power plan” and “high-performance power plan”.

High perf allows turbo boosting

6. ( 1 pt) What are the advantages of running a CPU with a guaranteed thermal limit in a datacenter?

Limits the maximum current drawn. Current usage beyond a limit costs heavily for DCs.
Won’t exceed cooling capacity. Reliability benefits. good usage of space.

7. ( 1 pt) Why does a benchmark simulating a High Performance Computing situation not applicable for
a data center?
HPC datacenters usually run at higher utilization (say 50 to 90%) than typical data centers (30 to
60%). Also these workloads may be compute intensive as opposed to I/O intensive for typical data
centers.

8. ( 1 pt) Why do system administrators of data centers try to avoid letting CPU utilization rise above
70% where CPUs may be most efficient?

Usually SLA are based on response time. At high utilization the response time increases
exponentially leading to frequent SLA violations.

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