J. E. Smith

June 2007

CMP Resource Management:CMP Resource Management:Primitives, Not SolutionsPrimitives, Not Solutions

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Objectives

Separate Objectives, Policies, MechanismsSeparate Objectives, Policies, Mechanisms

Leads to flexible, well-structured solutions

Policies

CapacityResource

BandwidthResource

CapacityResource

Mechanisms

BandwidthResource

Software

Hardware

Hardware provides mechanisms;

OS provides policies

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What is the Problem?What is the Problem?

Conventional Systems• Shared resources are processor(s) and real memory• OS policies manage resource*time• OS policies time-slice processor(s) and manage real memory• Mechanisms provided by ISA

Privileged mode, timer, page table, “touched” bits In CMPs

• Many shared resources– caches, memory ports– both bandwidths and capacities

• SMT even more sharing• No ISA mechanisms for direct control

Provide OS with suitable mechanisms for CMP resource management

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Path of Least ResistancePath of Least Resistance

Hardware designers assume ISA is inflexible• No OS-visible mechanisms for managing CMP resources

Build mechanisms and policies into hardware• Example: ICOUNT in SMTs

Satisfy non-conventional objectives• Maximize aggregate IPC performance• Concurrent threads experience equal slow-down with respect to

running in isolation• Optimize harmonic mean performance among concurrent threads

Why trouble ourselves real architecture work?

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A Better PathA Better Path

OS and HW designers cooperate to define new mechanisms and ISA features

Mechanisms in hardware Policies in software

• As much as possible…• Otherwise general, parameterized policies in HW

Develop general interface • Example: page tables in current systems• This will be a challenge• Both technical and non-technical issues