Fail to hit ideal time for PageRankDynamic with high granularity

[Khang Bùi]

Hi, I finished implementation for PageRankDynamic, and my results passed validation in terms of correctness. However, my execution time hovers around 42 - 45 seconds compared to expected time of 36 seconds - this is on cloud-02.

For granularity, it performs normally and lower than expected time - 92 seconds, mine hitting around 80 seconds. So, I'm puzzled by where the issues could be.

My implementation used compare_and_exchange in a while loop for getNextVertex(), and only used 2 original barriers.

If anyone has encountered this issue, please tell me what's your problem and how you fixed it. Thank you.

Here's my implementation (for prof and TA) : https://github.com/CMPT-431-SFU/assignment-5-pkbui/blob/master/pagerank/pagerank_parallel.cpp

[Khang Bùi]

To specify, I meant it's hitting expected time for granularity 1 but fails at granularity 4000. Sorry for lack of details.

[Ivan Jonathan Hoo]

Might not be the getNextVertex, I used that loop way too for getNextVertex and my time for 4000 is lower 29s which is lower than expected. I even have more barriers than you (4 barriers).

On Friday, March 27, 2020 at 2:04:28 AM UTC-7, Khang Bùi wrote:

[Arrvindh Shriraman]

Please mention machine when you quote #s. The validation scripts as mentioned on the page are for 02

Arrvindh Shriraman
Associate Professor
Computer Science
Simon Fraser University

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[Ivan Jonathan Hoo]

Sorry, 29s for me is on cloud-02 using the validation script.

On Friday, March 27, 2020 at 4:28:46 PM UTC-7, Arrvindh Shriraman wrote:

Please mention machine when you quote #s. The validation scripts as mentioned on the page are for 02

Arrvindh Shriraman
Associate Professor
Computer Science
Simon Fraser University

On Fri, Mar 27, 2020 at 4:27 PM Ivan Jonathan Hoo <ivank...@gmail.com> wrote:

Might not be the getNextVertex, I used that loop way too for getNextVertex and my time for 4000 is lower 29s which is lower than expected. I even have more barriers than you (4 barriers).

On Friday, March 27, 2020 at 2:04:28 AM UTC-7, Khang Bùi wrote:

Hi, I finished implementation for PageRankDynamic, and my results passed validation in terms of correctness. However, my execution time hovers around 42 - 45 seconds compared to expected time of 36 seconds - this is on cloud-02.

For granularity, it performs normally and lower than expected time - 92 seconds, mine hitting around 80 seconds. So, I'm puzzled by where the issues could be.

My implementation used compare_and_exchange in a while loop for getNextVertex(), and only used 2 original barriers.

If anyone has encountered this issue, please tell me what's your problem and how you fixed it. Thank you.

Here's my implementation (for prof and TA) : https://github.com/CMPT-431-SFU/assignment-5-pkbui/blob/master/pagerank/pagerank_parallel.cpp

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[Khang Bùi]

I eventually figured it out. It seems the performance problem comes from having conditional branch in my operator() function. When I refactored the code to not use any if statement inside the while loop, the performance meets the expectation.