J. E. Smith June 2007

1. CMP Resource Management: Primitives, Not Solutions J. E. Smith June 2007

2. Objectives 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 WIOSCA (c) 2007, J. E. Smith

3. 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 WIOSCA (c) 2007, J. E. Smith

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? WIOSCA (c) 2007, J. E. Smith

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 WIOSCA (c) 2007, J. E. Smith