A file server receives requests via a network. It takes 10 ms to dispatch the re

Question

A file server receives requests via a network. It takes 10 ms to dispatch the requested data and do the necessary processing, assuming that the data needed are in the disk cache. When there is a cache miss, as is the case in one third of the time, 45 ms is required to read the requested data from the hard disk into main memory (during which time the thread is blocked). (a) How many requests/sec can the server handle if it is single threaded? 8 marks (b) How many requests/sec can the server handle if it is multithreaded (one thread popping up at each request)?

Explanation / Answer

A)

Suppose the server can process at most n requests per second.

Then we have for single threaded server case, n*0.67*10+n*0.33*(10+45)<=1000

Therefore, n<=24.85

B)

For multithreaded server,

The cpu is never idle as long as there are pending requests. So, we can keep processing new requests when some requests go for disk I/O.

So, n= 1000/10

=100

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