Data Hazards [GateBook]

Question

Comments

Why 2? Debashish Deka
Getting 4 hazards

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@thor  LW R2,0(R1) means add 0 to R1 and load it in R2.

LW is Load Word..

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I1 – I3 won’t be a hazard since any hazard involving I1 is resolved by a stall during I2. There is a data dependency between I1 and I3, but no hazard. Answer should be 2.

Answer 1

RAW hazards:-

1) I₁-I₂

2) I₁- I₃

3) I₂-I₄

4) I₃-I₄

 Option C should be correct.

Comments

but it is not necessary that raw hazards occur between two adjacent instruction.

ryt???

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@Shubhanshu ryt.

As data hazards occur when instructions that exhibit data dependence, modify data in different stages of a pipeline.

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dont confuse raw dependency with raw hazard ....

if raw dependency cause pipeline to stall then it will be count as raw hazard.

here instruction 2 has stall of 2 cycle due to raw dependency on I-1

and I-4 also cause 2 stalls due to raw dependency on I-3

so total 4 hazard option c is correct

Answer 2

Answer should be 2

In RAW hazard or true data dependency we see for dependency between adjacent instructions only..

I.e. I1- I2 AND I3- I4

Comments

@vamp_vaibhav

read this:- https://courses.cs.washington.edu/courses/cse378/09au/lectures/cse378au09-15.pdf