The Impact of Performance Asymmetry in Multicore Architectures Saisanthosh Ravi Michael Konrad...

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The Impact of Performance Asymmetry in Multicore Architectures Saisanthosh Ravi Michael Konrad Balakrishnan Rajwar Upton Lai UW-Madison and , Intel Corp. nd Annual International Symposium on Computer Architecture

Transcript of The Impact of Performance Asymmetry in Multicore Architectures Saisanthosh Ravi Michael Konrad...

The Impact of Performance Asymmetry in

Multicore Architectures

SaisanthoshRavi

MichaelKonrad

BalakrishnanRajwarUptonLai

UW-Madison and , Intel Corp.

32nd Annual International Symposium on Computer Architecture

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Performance asymmetry

- Architectural differences- Micro-architectural parameters- Other

- Heat: Thermal throttling

Why need asymmetry now?

- CMP/ Many cores as commodity systems- Run variety of workloads - Good serial performance and high throughput- Optimal energy consumption

... difference in compute power of processors

Assume an asymmetric multicore system

F FS S

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Asymmetry & MT workloads

Perf

orm

an

ce

Compute power

Scalable?

N procs. Diff configs.

Need to utilize asymmetry. perform better

Need predictable and robust performance

F FS S

S SS S

Perf

orm

an

ce

Same/Many Runs

Stable?

N procs. Same config.

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The problems

Algorithm, Correctness, Thread Partitioning

ProgrammersDon’t reason about asymmetry

Characteristics of threadsPartitioning, Synchronization barriers, Interference, Lifetime

Scheduling of threadsOS Kernel, Library, Application, DB/Web

servers,Managed runtime systems (Java, .NET)

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Configurations

F F

F F S S

S S F F

S S

F F

F S

F S

SS

Symmetric Asymmetric

all fast all slow 1 slow 2 slow 3 slow

F = Full frequency

S = one-eighth of Full frequency (in talk and paper) S = one-fourth of Full frequency (in paper)

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Studying impact

3 s

low

2 s

low

1 s

low

all s

low

all f

ast

Perf

. M

etr

ic

(Asymm)

Sam

e o

rM

an

y r

un

s

Perf

. M

etr

ic

Scalability Stability

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SPECjbb

SPECjAppServer

Apache

Zeus

TPC-HSPECOMP

H.264

PMake

Impact of asymmetry

Scalable StableWorkloads

Fix

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SPECjbbStability (JRockit/Gencon GC) on 2 slow

- Problem: Interference from runtime system (JVM, GC)

4 runs

with kernel fix

- Fix: Kernel scheduler moves jobs from slow to fast if free

Scalable? Stable?

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Apache

- Problem: light load - threads can be on fast/slow- No issues under heavy load

- Fixes: Kernel scheduler or shorter lifetime of threads

Scalability & Stability (light load)

Stable?Scalable?

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ZeusScalability & Stability

- Under heavy and light loads: unpredictable- Superior perf. on symmetric configs.

- Problem: Aggressive application-level scheduling

Stable?Scalable?

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SPECOMP

- OpenMP schedules tasks assuming equal perf. procs.- Problem: Fast processors are held by slow

Scalability

with app. fix

- Fix: Change scheduling of tasks to on-demand- Downside: Overheads

Scalable? Stable?

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H.264 & PMake

- H.264 slows down significantly with 1 slow proc.

- Speeds up with 1 fast proc.

H.264 PMake

- PMake linearly scalable on all configurations

Scalable? Stable?

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Conclusions

Asymmetric systems - Good for energy and performance- But can introduce unpredictability

Software to understand asymmetry- Evaluate application’s work partitioning- Scheduling of tasks. Mostly no other changes.- May be, feedback based

Suitable asymmetry- Many slow & few fast processors