1. Dr. Alexandra Fedorova August 2007 Introduction to Systems Research at SFU

2. 2 CMPT 401 Summer 2007 © A. Fedorova 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 –Master’s and Ph.D.

3. 3 CMPT 401 Summer 2007 © A. Fedorova 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. 4 CMPT 401 Summer 2007 © A. Fedorova Systems Research at SFU System software design for chip multithreading processors Computer Architecture Distributed Systems

5. 5 CMPT 401 Summer 2007 © A. Fedorova System Software Design for Chip Multithreading Processors What is chip multithreading? Why is this research relevant? What research problems are we addressing?

6. 6 CMPT 401 Summer 2007 © A. Fedorova Chip Multithreading (CMT) Conventional processor: one software thread runs on a chip at a given instant: Level-1 cache A CHIP Level-2 cache CMT processors: multiple threads runs on the same chip simultaneously:

7. 7 CMPT 401 Summer 2007 © A. Fedorova 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. 8 CMPT 401 Summer 2007 © A. Fedorova 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 there’s 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. 9 CMPT 401 Summer 2007 © A. Fedorova CMT: More Efficient CPU Utilization time 1:add2:subtract4:load data from memory 3:load data from cache stall the pipeline 2:add 1:load data from memory 3:subtract thread 1 4:add thread 0 Stall the pipeline Pipeline is busy

10. 10 CMPT 401 Summer 2007 © A. Fedorova How to Enable CMT? How to enable running multiple threads on the same chip? –Hardware multithreading –Multicore processing –Combination of the two

11. 11 CMPT 401 Summer 2007 © A. Fedorova 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 Level-1 cache A CHIP Level-2 cache

12. 12 CMPT 401 Summer 2007 © A. Fedorova 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 L1 cache A CHIP L1 cache L2 cache

13. 13 CMPT 401 Summer 2007 © A. Fedorova Multicore + Multithreading A multicore processor Each core is multithreaded Multicore and multithreaded processors: –Sun Microsystems Niagara –IBM Power5, Power6 L1 cache A CHIP L1 cache L2 cache

14. 14 CMPT 401 Summer 2007 © A. Fedorova 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. 15 CMPT 401 Summer 2007 © A. Fedorova 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 Let’s look at a few examples…

16. 16 CMPT 401 Summer 2007 © A. Fedorova Constructing Optimal Co-schedules L1 cache A CHIP L1 cache L2 cache 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

17. 17 CMPT 401 Summer 2007 © A. Fedorova 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 application’s cache usage patterns are incompatible with another’s? 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. 18 CMPT 401 Summer 2007 © A. Fedorova 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) L1 cache A CHIP L1 cache L2 cache

19. 19 CMPT 401 Summer 2007 © A. Fedorova Scheduling On HMC Systems L1 cache Core 1 A CHIP L1 cache Core 2 L2 cache Set A: Want to run on Core 1 Set B: Want to run on Core 2

20. 20 CMPT 401 Summer 2007 © A. Fedorova 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 they’d 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. 21 CMPT 401 Summer 2007 © A. Fedorova 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