Dr. Alexandra Fedorova

1
Introduction to Systems Research at SFU

• Dr. Alexandra Fedorova
• August 2007

2
Introduction

• Systems software systems, hardware systems, the
  interaction between them
• New research area at SFU, before December 2006
  there were no faculty members at SFU doing
  systems research (not counting networking)
• Research opportunities at undergraduate and
  graduate level
• Undergraduate honours thesis
• CMPT 415
• Paid research assistanships
• Masters and Ph.D.

3
What is Systems Research?

• System a collection of software and hardware
  components that accomplish a certain goal
• Usually this does not include applications, but
  includes system software
• The operating system
• System libraries
• Systems research concerns with building these
  components and structuring their interaction

4
Systems Research at SFU
System software design for chip multithreading
processors
Computer Architecture
Distributed Systems
5
System Software Design for Chip Multithreading
Processors

• What is chip multithreading?
• Why is this research relevant?
• What research problems are we addressing?

6
Chip Multithreading (CMT)

• Conventional processor one software thread runs
  on a chip at a given instant

• CMT processors multiple threads runs on the same
  chip simultaneously

A CHIP
Level-2 cache
7
CMT The Dominant Architecture

• Most new processors are CMT
• Intel 100 of new server processors and 90 of
  high-performance desktop processors are CMT by
  the end of 2007
• All major hardware vendors are in the CMT
  business
• Sun Microsystems Niagara (32 threads on the chip)
• IBM Power4, Power5, Power6
• Intel Hyper-threaded Xeon (servers, desktops)
• Intel Core Duo (desktops and laptops)
• Dell Quad core systems (2x Intel Dual-core
  processors)
• AMD Quad core (coming up in Fall 2007)

8
Why CMT?

• Running one thread per chip is inefficient
• Due to nature of modern applications,
  computational hardware is underutilized
• Modern applications spend 50-60 of their CPU
  time accessing memory
• While memory is accessed CPU pipeline is stalled
  it is idle, not doing anything useful
• But while it is stalled, CPU is still consuming
  power
• So theres power waste with no benefit
• Idea behind CMT while one thread stalls the
  pipeline, let another thread use it
• Sort of like overlapping I/O and computation but
  at the micro level

9
CMT More Efficient CPU Utilization
Stall the pipeline
Pipeline is busy
stall the pipeline
1add
2subtract
4load data from memory
3load data from cache
thread 0
10
How to Enable CMT?

• How to enable running multiple threads on the
  same chip?
• Hardware multithreading
• Multicore processing
• Combination of the two

11
Hardware Multithreading

• Run at least two threads on the same processing
  core
• Some hardware is duplicated, some is shared
• Shared hardware
• Pipeline i.e., functional units, register files,
  queues
• Caches Level-1 (L1) instruction and data caches,
  Level-2 (L2) unified cache
• Interconnects
• Multithreaded processors
• Intel Hyper-threaded Xeon
• IBM Power5, Power6, Cell
• Sun Microsystems Niagara

A CHIP
Level-2 cache
12
Multicore Processing

• Multiple processing cores on the same chip
• Threads share the L2 cache (and other lower-level
  caches), and interconnects
• Multicore processors
• Intel Core Duo
• AMD Quad Core
• IBM Power4, 5, 6
• Sun Microsystems Niagara

A CHIP
L2 cache
13
Multicore Multithreading

• A multicore processor
• Each core is multithreaded
• Multicore and multithreaded processors
• Sun Microsystems Niagara
• IBM Power5, Power6

A CHIP
L2 cache
14
Research on CMT Processors

• Computer architecture research
• How to design a CMT processor to achieve a good
  combination of CPU utilization, application
  performance, power efficiency
• System software research
• How to design system software, i.e., the
  operating system, that enables applications to
  perform well on these processors?

15
OS Design for CMT Processors

• Operating systems are traditionally responsible
  for the allocation of hardware resources
• On CMT processors, on-chip resources are shared
  among threads that run simultaneously
• How you allocate those resources among threads
  determines the performance that those threads
  will achieve
• Lets look at a few examples

16
Constructing Optimal Co-schedules
A CHIP

• Blue suffers when it does not have enough L1
  cache,
• Red uses lots of L1 cache
• Green does not use much L1 cache
• Yellow does not suffer when it does not have much
  L1 cache

L2 cache
17
Constructing Optimal Co-schedules (cont.)

• How do we find out applications cache behaviour?
• Turns out you need to consider memory access
  patterns - this is not trivial to measure
• How do you model interactions among applications?
  
• How do you know if one applications cache usage
  patterns are incompatible with anothers?
• These patterns/relationships cannot be measured
  directly
• Can they be modeled?
• Simple models are inaccurate
• Complex models are too inefficient to use inside
  an operating system scheduler
• Approach of my group use learning methods,
  feedback-directed scheduling

18
Heterogeneous Multicore Systems

• One size does not fit all
• Application class A runs best on core with
  feature set X
• Application class B runs best on core with
  feature set Y
• Rather than designing a homogeneous multicore
  system that attempts to satisfy everyone but
  satisfies no one, design a heterogeneous
  multicore system (HMC)

A CHIP
L2 cache
19
Scheduling On HMC Systems
Set A Want to run on Core 1
A CHIP
Set B Want to run on Core 2
L2 cache
20
Scheduling On HMC Systems

• If you schedule all threads in Set A on their
  preferred core, those threads will suffer from
• Low amount of CPU time
• High response time
• Because there is high demand for that core, and
  theyd have to share it with others
• So you might want to schedule threads on their
  non-preferred core once in a while
• How do you balance between performance, fair CPU
  allocation and good response time?

21
Summary

• CMT systems are new and cool, yet prevalent
  enough for people to care about them
• Companies are desperate to hire students with
  experience on CMT systems
• If you are thinking about academic career new
  and hot research area
• Many problems
• Many opportunities to publish
• Talk to me if you are interested in research
  opportunities
• Tell your friends who might be interested