6.9 Consider the following three CPU organizations: CPU SS: A 2-core suprescalar

Question

6.9 Consider the following three CPU organizations:

CPU SS: A 2-core suprescalar microprocessor that provides out-of-order issue capabilities on 2 function units (FUs). Only a single thread can run on each core at a time.

CPU MT: A fine-grained multithreaded processor that allows instructions from 2 threads to be run concurrently (i.e., there are two functional units), though only instructions from a single thread can be issued on any cycle.

CPU SMT: An SMT processor that allows instructions from 2 threads to be run concurrently (i.e., there are two functional units), and instructions from either or both threads can be issued to run on any cycle.

Assume we have two threads X and Y to run on these CPUs that include the following operations:

Assume all instructions take a single cycle to execute unless noted otherwise or they encounter a hazard.

6.9.4 [10] <§6.4> Assume you have 1 SMT CPU. How many cycles will it take to execute the two threads? How many issue slots are wasted due to hazards?

Thread X Thread Y A1 - takes cycles to execute B1 - takes 2 cycles to execute A2 - no dependencies B2 - conflicts for functional unit with B1 A3 - conflicts for a functional unit with A1 B3 - depends on the result of B2 A4 - depends on the result of A3 B4 - no dependencies and takes 2 cycles to execute

Explanation / Answer

The slots used will be the ones as shown in table:

So 9 out of the 16 slots will be used and therefore the 56% slot usage will be there.

7 slots will be wasted.

Core1 Core2 A1 A3 B1, B3 A1 B2 A2 B4 A4

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