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arvin99
Adept II

program counter in instruction vs program counter in wavefront

Hi,

I have two questions.

As I know that each wavefront has its own program counter.

So,

1. what is the different between program counter for wavefront and program counter for each instruction??

2. what is the different between instruction pointer and program counter for each instruction?? (looks like they are same, but not sure 100%)


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arvin99 wrote:



Thanks for reply, I already clear about the answer from question 2.


But your answer in question number 1 still make me confuse.



So, in GPU and CPU, there is only one program counter.


The differences are:


In CPU the process PC->PC +1 happened in each cycle clocks but in GPU the process PC-> PC +1 happened for each four cycle clocks (since GPU execute on a group of thread (wavefront)).



Am I right??


CPU

1. There is one program counter (PC).

2. If the CPU chip has multiple cores/threads, there is 1 PC per thread.

3. PC will advance after the instruction is finished, it can be 1 to 100+ clocks, depends on instruction. **

GPU

1. There is 1 PC per wave, each wave has 64 (usually) threads. There are many waves.

2. Almost all instructions advance the PC every 4 clocks.

3. On a CU, 4 waves execute in parallel, so the average time to execute 1 instruction is 1 clock, not 4.

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