The Impact of Performance Asymmetry in Multicore Architectures Saisanthosh Ravi Michael Konrad...
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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
2
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
3
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.
4
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)
8
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)
9
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
11
SPECjbb
SPECjAppServer
Apache
Zeus
TPC-HSPECOMP
H.264
PMake
Impact of asymmetry
Scalable StableWorkloads
Fix
13
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?
15
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?
16
ZeusScalability & Stability
- Under heavy and light loads: unpredictable- Superior perf. on symmetric configs.
- Problem: Aggressive application-level scheduling
Stable?Scalable?
18
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?
19
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?
21
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