Client Pairing A Framework for Implementing Coherence Hierarchies Jesse G Beu Michael C Rosier Thomas M Conte Tinker Research Georgia Institute of Technology The Problem Coherence protocols can be difficult to design properly ID: 186992
Download Presentation The PPT/PDF document "Manager" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Manager-Client Pairing: A Framework for Implementing Coherence Hierarchies
Jesse G. BeuMichael C. RosierThomas M. Conte
Tinker ResearchGeorgia Institute of TechnologySlide2
The Problem
Coherence protocols can be difficult to design properlyIntegration of coherence protocols is even more difficultLeads to monolithic, homogenous coherence in a heterogeneous future
Directory MESISlide3
The Solution
Use existing protocols as building blocksEnable coherence integration and compositionLeads to heterogeneous hierarchies in a heterogeneous futureDesign using best local protocol for the ‘common case’
Directory MESI
Broadcast
MSI
Broadcast
MSI
Token RingsSlide4
Width Variation Observation
Ocean_C
while varying tier width at fixed 2-levelL2 HitOff-ChipSlide5
Manager-Client PairingSlide6
OutlineMotivation
Introduce Manager-Client PairingCommunication Similarity and RecursionTypes of ActionQuery, Get and Grant
MCP Algorithm and ExampleImpact of Tier Width and Hierarchy HeightFuture Work and ConclusionSlide7
Self-Similarity for Recursion
Processor <-> CacheRequest DataTransparently asks if we have permissionGets permission if notCache supplies DataCache <-> Memory
Request DataMemory supplies DataAdd ‘asking’ featureInternals of each layer can be ‘black-boxed’Slide8
Types of ActionsQuery – Permission Query to check permission
levelGet – Request permissions and DataRead and Write Permission, supplying DataPermission upgrade (e.g. Shared -> Modified)
Grant – Response to earlier Get requestSlide9
Manager and Client PairSlide10
MCP Algorithm
Load
GetGrantProcessorSlide11
Example – Realm HitSlide12
Example – Realm Miss
Downgrade
II
I
I
E
M
MSlide13
Latency Impact of Hierarchies Strong analogy with cache design
Tier width (# of clients) <-> cache sizingSmaller Tiers result in ‘lower capacity’ with ‘faster access’Larger Tiers have ‘higher capacity’ with ‘slower access’Hierarchy height (# of tiers) <-> cache levels
Motivation of this work!Single flat protocol won’t scaleAnalogous to having a monolithic cacheDeeper hierarchies are not always goodBenefit of smaller, fast tiers while retaining capacityMake too small and the lowest level will frequently missAdditional penalty of hierarchy indirectionConsider L3/L4 Caches vs. larger L2/L3 cachesSlide14
Tier Width
Home Node
Realm Hit
Realm MissSlide15
Width Variation Observation
Ocean_C
while varying tier width at fixed 2-levelSlide16
Future WorkMCP’s role in Validation
Willing to discuss off-lineProtocol interactions/selectionProtocol and NOC topology co-designHierarchical topologiesCross-vendor coherence integrationSlide17
ConclusionMCP does address concerns regarding future coherence
Uses existing protocols as building blocksEnables coherence integration and compositionDemonstration of rapid development of a variety of hierarchy configurations
MCP provides a generic coherence hierarchy composition framework to support continued scaling of diverse, massively coherent systemsSlide18
Questions?
Thank you!