9 - parallel computing Flashcards

1
Q

Moore’s Law

A

Number of transistors doubles every ~2 years.
Observation that is not a law

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2
Q

Why parallel computing?

A

Single core performance increase each year is no longer significant enough after 2002

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3
Q

Why can frequency not be increased?

A

Physical limits
- Electrical Leakage
- Hear dissipation
- Extreme size of transistors
- Increased cooling costs

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4
Q

FPGA

A

Field Programmable Gate Array

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5
Q

HPC system components

A

Compute nodes
Fast interconnect
Parallel filesystem
Scheduler

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6
Q

HPC Programs

A

Remote, non-interactive usage.

Submit jobs (no interaction), user gets results on completion

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7
Q

Supercomputer

A

Cabinets with servers

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8
Q

500 rankings

A

TOP 500 - FLOPS
green 500 - ordered by FLOPS/watts

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9
Q

Is it assumed that time to communicate is completed in parallel in parallel computations?

A

NO

Assume that a controller cannot communicate to multiple places at once

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10
Q

Compute to communication ratio, in the context of addition on a stack

Give the symbols and expression

A

α - time to perform single addition
β - time to communicate a stack of numbers
γ = α / β is the ratio

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11
Q

Amdahl’s Law

A

Bound for max speedup

(1 core runtime)/(p cores runtime)

1/(s+(1-s)/p)

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12
Q

Speedup bottlenecks

A

Communication
Sync
Not all parts are parallelisable

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13
Q

Amdahl Law Assumptions

A

Fixed workload
Serial fraction s cannot be parallelised
Parallelisable fraction 1-s CAN be parallelised

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14
Q

Amdahl’s Law infinite core maximum speedup

A

1/s

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15
Q

Gustafson’s Law definition (question: given the workload on one core….)

A

Given the amount of workload on one core, how much more can be achieved on p cores

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16
Q

Gustafson’s Law expression

A

Ss(p,n) = s + p * (1-s)

17
Q

Gustafsons Law Infinite cores…

A

Infinite speed up given infinite workload

18
Q

Shared Memory

A

Multiple processors share memory, might have own cache though