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Performance Pathologies in Hardware Transactional Memory

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Presentation on theme: "Performance Pathologies in Hardware Transactional Memory"— Presentation transcript:

1 Performance Pathologies in Hardware Transactional Memory
Jayaram Bobba, Kevin E. Moore, Haris Volos, Luke Yen, Mark D. Hill, Michael M. Swift, and David A. Wood Multifacet Project ( Computer Sciences Dept., University of Wisconsin Madison

2 Executive Summary (1/2) Multiple Hardware Transactional Memory Designs
Best Performance ? Depends ! Livelock © 2007 Multifacet Project University of Wisconsin Madison

3 Executive Summary (2/2) Why? Performance Pathologies What to do?
Better Conflict Resolution pa●thol●o●gy: any deviation from a normal, healthy or efficient condition Livelock Performance Pathologies Performance © 2007 Multifacet Project University of Wisconsin Madison

4 Talk Outline Motivation Base HTM Results Performance Pathologies
Enhanced HTM Systems © 2007 Multifacet Project University of Wisconsin Madison

5 Motivation Which HTM system performs best? Different Assumptions
Hardware Broadcast vs Directory Based Software: Continuous Transactions vs Critical Section Transactions How to compare? © 2007 Multifacet Project University of Wisconsin Madison

6 LL EE EL HTM Design Space Version Management Conflict Detection
Lazy Eager Stanford TCC Illinois Bulk LL No HTMs (yet) Herlihy/Moss TM MIT LTM Intel/Brown VTM MIT UTM Wisconsin LogTM EL EE Conflict Resolution: Adhoc “Better By Design” ? © 2007 Multifacet Project University of Wisconsin Madison

7 LL EL EE Experimental Setup Base HTM Systems Common Hardware Platform
32 core CMP Directory-Based Coherence Common TM Programming Model Critical Section Based Transactions Common Workloads 5 SPLASH + 2 Microbenchmarks (Btree, LFUCache) LL EL EE © 2007 Multifacet Project University of Wisconsin Madison

8 Performance Pathologies
And the winner is… Performance Pathologies Livelock Low Contention: Similar High Contention: Depends © 2007 Multifacet Project University of Wisconsin Madison

9 Talk Outline Motivation Base HTM Results Performance Pathologies
Enhanced HTM Systems © 2007 Multifacet Project University of Wisconsin Madison

10 Performance Pathologies
StarvingElder SerializedCommit RestartConvoy FriendlyFire DuelingUpgrades FutileStall StarvingWriter EE EL LL © 2007 Multifacet Project University of Wisconsin Madison

11 LL System Conflict Detection: Lazy Version Management: Lazy
Detect conflicts at commit time (Validation) Version Management: Lazy New value elsewhere, Update on commit + Abort - Commit Conflict Resolution: Committer Wins compare with TCC, Bulk © 2007 Multifacet Project University of Wisconsin Madison

12 StarvingElder CAUSE Committer Wins Time EFFECT(S) Starvation
Load Imbalance FIX Elder gets Priority ? T1 T2 T3 store A load A ABORT Time store A load A ABORT store A load A ABORT COMMITING STALLED ABORTING © 2007 Multifacet Project University of Wisconsin Madison

13 RestartConvoy CAUSE Fast Abort + Immediate Restart EFFECT(S)
Resource Contention Serialized Execution ≈ Lock Convoys FIX Stagger Restarts ? T2 T3 T4 load A store A ABORT load A store A ABORT load A © 2007 Multifacet Project University of Wisconsin Madison

14 LL LL LL_B Pathologies Pathology (% ExecutionTime) Enhancement
Linear Backoff on Abort Eliminate RestartConvoys StarvingElder Serialized Commit Restart Convoy SerializedCommit Raytrace 45 27 5.2 0.1 0.3 1.0 LL LL_B © 2007 Multifacet Project University of Wisconsin Madison

15 LL_B LL_B LL Enhanced LL ( ) Pathology (% ExecutionTime) Performance
StarvingElder Serialized Commit Restart Convoy SerializedCommit Raytrace 45 27 5.2 0.1 0.3 1.0 LL LL_B © 2007 Multifacet Project University of Wisconsin Madison

16 Performance Pathologies
StarvingElder SerializedCommit RestartConvoy FriendlyFire DuelingUpgrades FutileStall StarvingWriter LL EL EE © 2007 Multifacet Project University of Wisconsin Madison

17 EL System Conflict Detection: Eager Version Management: Lazy
Detect conflicts immediately Version Management: Lazy New Value elsewhere, Update on commit + Abort - Commit Conflict Resolution: Requester Wins Exponential Backoff on Abort compare with HMTM, LTM © 2007 Multifacet Project University of Wisconsin Madison

18 FriendlyFire CAUSE Requester Wins EFFECT(S) Unnecessary Aborts
load A store A ABORT CAUSE Requester Wins EFFECT(S) Unnecessary Aborts Livelock FIX Priority Based Conflict Resolution ? load A store A ABORT © 2007 Multifacet Project University of Wisconsin Madison

19 EL EL EL_T Pathologies Pathology (% ExecutionTime) Enhancement
Timestamp Based Conflict Resolution Eliminate FriendlyFire Friendly Fire FriendlyFire Raytrace 73 0.2 EL EL_T © 2007 Multifacet Project University of Wisconsin Madison

20 EL_T EL EL_T Enhanced EL ( ) Pathology (% ExecutionTime) Performance
Friendly Fire FriendlyFire Raytrace 73 0.2 EL EL_T © 2007 Multifacet Project University of Wisconsin Madison

21 Performance Pathologies
StarvingElder SerializedCommit RestartConvoy FriendlyFire DuelingUpgrades FutileStall StarvingWriter LL EL EE © 2007 Multifacet Project University of Wisconsin Madison

22 EE System Conflict Detection: Eager Version Management: Eager
Detect conflicts immediately Version Management: Eager New Value in-place, Restore on Abort - Abort + Commit Conflict Resolution Stall Requester Abort Requester on possible deadlock (Conservative Deadlock Avoidance) compare with LogTM © 2007 Multifacet Project University of Wisconsin Madison

23 DuelingUpgrades CAUSE Conservative Deadlock Avoidance EFFECT(S)
load A store A T1 T2 STALL ABORT CAUSE Conservative Deadlock Avoidance EFFECT(S) Unnecessary Stall Unnecessary Abort FIX Acquire Store Permissions Early ? © 2007 Multifacet Project University of Wisconsin Madison

24 StarvingWriter CAUSE Stall Requester EFFECT(S) Starvation
store A load A T1 T2 T3 T4 CAUSE Stall Requester EFFECT(S) Starvation Load Imbalance ≈ Reader/Writer Locks FIX Writer Priority ? © 2007 Multifacet Project University of Wisconsin Madison

25 EE EE_HP EE Pathologies Pathology (% ExecutionTime) Enhancements
DuelingUpgrades: Store-Set Predictor StarvingWriter: Writer Aborts Readers immediately % Execution Time Aborts /Transaction FutileStall StarvingWriter Dueling Upgrades Futile Stall Raytrace 1.0 4.6 4.2 <0.1 0.3 EE EE_HP © 2007 Multifacet Project University of Wisconsin Madison

26 EE_HP EE EE_HP Enhanced EE ( ) Pathology (% ExecutionTime) Performance
Aborts /Transaction FutileStall StarvingWriter Dueling Upgrades Futile Stall Raytrace 1.0 4.6 4.2 <0.1 0.3 EE EE_HP © 2007 Multifacet Project University of Wisconsin Madison

27 LL LL_B Caveats / FutureWork High Contention Scenarios
Restart Convoy StarvingElder Serialized Commit RestartConvoy SerializedCommit Mp3d 21 36 30 9.0 28 25 High Contention Scenarios Better Conflict Resolution Unidentified Pathologies Better TM Workloads LL LL_B © 2007 Multifacet Project University of Wisconsin Madison

28 Executive Summary Performance Pathologies Enhanced HTM systems
Livelock © 2007 Multifacet Project University of Wisconsin Madison

29 FutileStall DuelingUpgrades FriendlyFire RestartConvoy StarvingWriter StarvingElder SerializedCommit

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