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29 Pages·2013·1.69 MB·English

Steal Tree: Low-Overhead Tracing of
Work Stealing Schedulers
JonathanLifflander*,SriramKrishnamoorthy ,LaxmikantV.Kale*
†
jliffl2,kale @illinois.edu,[email protected]
{ }
*UniversityofIllinoisUrbana-Champaign
†PacificNorthwestNationalLaboratory
June19,2013
Motivation
Structuredparallelprogramming(e.g. async-finish)idiomshave
⌅
proliferated
I Examples: OpenMP3.0,JavaConcurrencyUtilities,IntelTBB,Cilk,
X10
Workstealingisoftenusedtoschedulethem:
⌅
I Well-studieddynamicloadbalancingstrategy
I Provablyefficientscheduling
I Understandableboundsontimeandspace
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Tracing
Whereandwheneachtaskexecuted
⌅
Capturestheorderofeventsandiseffectiveforonlineandoffline
⌅
analysis
Challenges
⌅
I Thesizemaylimitwhatcanbefeasiblyanalyzed
I Itmayperturbtheapplication’sexecutionmakingitimpractical
Applications
⌅
I Replay
I Performanceanalysis
I Data-racedetection,retentivestealing,...
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Trace Sizes Using the STEAL TREE
5
2000 Cores
4000 Cores
4 8000 Cores
16000 Cores
Core 3 32000 Cores
KB/ 2
1
0
AQ-HF AQ-WF SCF-HF SCF-WF TCE-HF TCE-WF PG-HF PG-WF
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Approach
Forasync-finishprogramstracingindividualtasksisnotfeasible
⌅
I Oftentheseprogramsexposefarmoreconcurrencythanthenumberof
threads
F Finegranularity
F Sheernumberoftasks
Ratherthantraceindividualtasks,exploitthestructureofthe
⌅
schedulertocoarsentheeventstraced
Weidentifykeypropertiesoftwoschedulingpolicies:
⌅
I Help-first: exposemoreconcurrencybyexpandingtasksinthecurrent
scopebeforeexecutingatask
I Work-first: depth-firsttraversalofthecode(Cilk)
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Example async-finish Program
fn() {
s1;
async {
s5;
async w;
s6;
}
s2;
finish {
s7;
async x;
s8;
async y;
s9;
async z;
s10;
}
s3;
async { s11; }
s4;
}
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Example async-finish Program
fn() {
s1;
Root of Computation
async {
s5;
Sequential Block async w;
s6;
}
Asynchronous Task s2;
finish {
s7;
Finish Scope
async x;
s8;
Continuation async y;
s9;
async z;
s10;
}
s3;
async { s11; }
s4;
}
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Help-first Scheduling Policy
Enqueueallasyncsinthecurrentleveluntilafinishisreached
⌅
Example Program Snapshot of Execution Deque
fn() {
steal end
s1; level
async {
s5; {
async w; 1 s1 s2 s3 s3
s6;
}
s2;
finish {
s7;
async x;
s8;
async y; local end
s9;
async z;
s10;
}
s3;
async { s11; }
s4;
}
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Help-first Scheduling Policy
Enqueueallasyncsinthecurrentleveluntilafinishisreached
⌅
Example Program Snapshot of Execution Deque
fn() { steal end
level
s1;
async {
s5; 1 { s1 s2 s3 s3
async w;
s6;
} {
s2; 2 s7 s8 s9 s10
finish {
s7;
async x;
s8; local end
async y;
s9;
async z;
s10;
}
s3;
async { s11; }
s4;
}
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Help-first Scheduling Policy
Enqueueallasyncsinthecurrentleveluntilafinishisreached
⌅
Example Program Snapshot of Execution Deque
fn() { steal end
s1; level
async {
s5; {
async w; 1 s1 s2 s3 s3
s6;
}
{
s2; 2 s7 s8 s9 s10
finish {
s7;
async x; 3 { z
s8;
async y; local end
s9;
async z;
s10;
}
s3;
async { s11; }
s4;
}
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