Finding effective average instruction execution time

Question

I find below problem a lot complex to solve:

 

A system uses 2 level paging schemes. A regular memory access takes 100 ns and servicing a page fault takes 10 ms. An average instruction takes 100 ns of cpu time and two memory access. The TLB hit ratio is 95% and page fault rate is one in every 10000 instruction.

What is the effective average instruction execution time?

(A)​ 1300 ns
(B) 1250 ns
(C) 1320 ns
(D) 1275 ns

 

Answer 1

Here goes the answer,

Although, the answer is coming to be 1310 ns, I guess the options are a bit incorrect.

I suppose during the exam I would safely go with option (c).

Answer 2

Effective average instruction execution time = cpu time for a instruction + avg page fault service time + effective memory access time

 

Here per instruction cpu time is 100 ns.

Average page fault service time is 10*10^6/10000 = 1000ns  (: 10^6 is for convert ms to ns)

Effective memory access time is 0.95*100+0.05*3*100 = 110 ns

Now effective average instruction execution time is 100+1000+2(110) = 1320ns    (: effective memory access time is multiplied by 2 because it is given in question that average instruction take two memory access) 

 

So ans is : option C 1320ns