J. E. Smith

1
CMP Resource Management Primitives, Not Solutions

• J. E. Smith
• June 2007

2
Separate Objectives, Policies, Mechanisms

• Leads to flexible, well-structured solutions

Hardware provides mechanisms OS provides policies
Policies
Software
Hardware
Mechanisms
Capacity
Bandwidth
Capacity
Bandwidth
Resource
Resource
Resource
Resource
3
What is the Problem?

• Conventional Systems
• Shared resources are processor(s) and real memory
• OS policies manage resourcetime
• 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

4
Path 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?

5
A 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