81 lines
1.7 KiB
Markdown
81 lines
1.7 KiB
Markdown
---
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dg-publish: true
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---
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4 de Outubro 2023 - #CP
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## Ex. 2
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#### a) Limitações vetoriais
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A -> consecutive elements in a row -> consecutive access in the vector
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C -> same element
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B -> consecutive elements in a collumn
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Não vai ser vetorizável.
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#### b) Enable vectorization
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result of change cycles to i, k , j :
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A -> same element
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C -> consecutive elements in a row -> consecutive access in the vector
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B -> consecutive elements in a row -> consecutive access in the vector
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i k j
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0 0 1
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Vai ser vetorizável.
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128b
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8B -> 64b
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2 elements
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Without vectorization:
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![[Pasted image 20231004115725.png]]
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With vectorization:
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![[Pasted image 20231004115135.png]]
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Estimated: ( n^3 / 2 )* 8
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#### c)Measure and analyze results
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| N | Version | Time | CPI | \#I |
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| --- | -------- | ---- | --- | --- |
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| 512 | base_v()| 0.492484818 | 0.91 | 1113554887 |
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| 512 | vect() | 0.081604350 | 2.88 | 578275097 |
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>[!note]- Commands run
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>module load gcc/9.3.0
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>gcc -O2 -ftree-vectorize -msse4 mmult.c
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>srun --partition=cpar perf stat -e cycles,instructions ./a.out
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#### d) Vectorization fine-tuning
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Ganhos de 4 vezes mais.
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## Ex. 3
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#### a) Peak Performance
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2 operações em FP
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4 elementos de cada vez em cada ciclo
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2.5 GHz -> 2.5 billion cycles per second
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conclusion: 20 GFlop/s
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#### b)
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peak with vectorization: 20 GFlop/s
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peak without vectorization: 5 GFlop/s
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memory bandwith limitation: 20 GFlop/s
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real achievable performance:
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measured performance:
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#### c)
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memory bandwith limitation
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| GFlop/s | Flop/Byte |
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| ------- | --------- |
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| 0.125 | |
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| 0.25 | |
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| 0.5 | 10 |
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| 1 | 20 |
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| 2 | |
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| 4 | |
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| 8 | |
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