Research

My research is currently focused on the performance of systems software. More specifically, I am investigating the interactions between modern computer architectures and systems software. One useful tool which I have worked with is the hardware performance counters found in most modern processors. I investigate software scalability in the face of current chip-multiprocessor and multithreaded hardware trends. My research at the University of Toronto has been performanced under the guidance of Michael Stumm.

A few years ago, I had the opportunity to hack the K42 research operating system, from which I have learned a great deal about operating-system structure, design and implementation. K42 is a research operating system designed for shared-memory multiprocessors with scalability and flexibility as its main goals.

For my Masters, I developed the K42 File System (KFS), including a concurrent port to the Linux kernel. The goal of KFS was to build an infra-structure for a flexible file-system where each file or directory can have distinct implementations (layout on disk and caching policies). During KFS' development I also developed a novel file-system consistency technique called meta-data snapshotting, which was possible given KFS' unique decentralized meta-data structure. This work was done at the University of São Paulo, under the guidance of Dilma Da Silva.

• 2012
  • Pointy: A Hybrid Pointer Prefetcher for Managed Runtime Systems
  • Ioana Burcea, Livio Soares, and Andreas Moshovos
    To appear: 21st International Conference on Parallel Architectures and Compilation Techniques (PACT 2012)
    
    
  • Operating System Techniques for Reducing Processor State Pollution
  • Livio Soares
    Thesis presented to the University of Toronto as requirement for my Ph.D.
    Advisor: Michael Stumm

• 2011
  • Exception-less System Calls for Event-Driven Servers
  • Slides: PDF [3.0MB]
    Presentation video: hosted at USENIX, may require membership.
    Livio Soares and Michael Stumm
    USENIX Annual Technical Conference (USENIX ATC'11)
    
    • This work extends the original exception-less system call mechanism to support event-driven servers, introducing a new library called libflexsc. We demonstrate that it is possible to modify event-driven servers that use Linux event-based primitives to use exception-less system calls by porting nginx and memcached to rely on libflexsc. We show performance improvements of up to 35% on memcached and up to 120% on nginx webserver.

  • Mind the Gap: Reconnecting Architecture and OS Research
  • Jeffrey C. Mogul, Andrew Baumman, Timothy Roscoe, and Livio Soares
    13th Workshop on Hot Topics in Operating Systems (HotOS 2011)
    
    • Position paper that argues the need for closer collaboration between the computer architecture and operating systems research communities. We outline some of the motivations for this need, as well as suggestions to help close the gap.

• 2010
  • FlexSC: Flexible System Call Scheduling with Exception-Less System Calls
  • Slides: PDF [5.1MB]
    Presentation video: hosted at USENIX, may require membership
    Livio Soares and Michael Stumm
    9th USENIX Symposium on Operating Systems Design and Implementation (OSDI 2010)
    
    • This work questions the 30+ year old system call mechanism operating systems use by quantifying the performace impact, at the processor level, of system calls for server workloads. We propose a new exception-less mechanism for system calls. Excepion-less system calls allows for flexibly scheduling operating system work, enabling run-time systems to greatly improve locality of execution, and consequently, performance. One interesting use-case of exception-less system calls is dynamic core specialization, where system calls are dynamically redirected to specific cores in a multi-core system, adapting to workload needs. We also describe a new threading package that transparently translates legacy system calls into exception-less ones. Using a Linux implementation of exception-less system calls (FlexSC) and a pthreads-compatible thread package (called FlexSC-Threads), we demonstrate a 2x speed-up for internet servers such as Apache and BIND.

• 2009
  • RapidMRC: Approximating L2 Miss Rate Curves on Commodity Systems for Online Optimizations
  • David Tam, Reza Azimi, Livio Soares, and Michael Stumm
    In the 14th International Conference on Architectural Support for Programming Languages and Operating Systems (ASPLOS 2009)
    
    • RapidMRC is an online tool for generating L2 MRCs targeted at dynamic optimizations in the run-time system. This work describes the underlying technique using Power5 hardware performance counters, as well as an interesting use-case for L2 MRCs: cache partitioning in a multi-core system.

  • Enhancing Operating System Support for Multicore Processors by Using Hardware Performance Monitoring
  • Reza Azimi, David Tam, Livio Soares, and Michael Stumm
    ACM SIGOPS Operating System Review (OSR) - Special issue on The Interaction Among the OS, the Compiler, and Multicore Processors, April 2009
    
    • This paper describes the work our group has been pursuing to improve performance of multi-core systems. We focused on dynamic operating system techniques that adapt using run-time hardware performance counters information.

• 2008
  • Reducing the Harmful Effects of Last-Level Cache Polluters with an OS-Level, Software-Only Pollute Buffer
  • Slides: PPT, PDF
    Livio Soares, David Tam and Michael Stumm
    In the 41st International Symposium on Microarchitecture (MICRO-41), Lake Como, Italy, 2008
    One of the eight papers nominated for the Best Paper Award by the Program Committee.
    
    • Describes a new software mechanism, "pollute buffer", that improves processor cache performance of cache/memory intensive applications. The OS profiles application's address spaces with hardware performance counters and re-maps polluter pages to a small partition of the processor cache. Performance of 5% to 35% improvement is obtained on commodity hardware.

• 2007
  • PATH: Page Access Tracking to Improve Memory Management
  • Reza Azimi, Livio Soares, Michael Stumm, Angela Demke-Brown, and Tom Walsh
    In International Symposium on Memory Management (ISMM 2007)

  • Experience Distributing Objects in an SMMP OS
  • Jonathan Appavoo, Dilma Da Silva, Orran Krieger, Marc Auslander, Michal Ostrowski, Bryan Rosenburg, Amos Waterland, Robert W. Wisniewski, Jimi Xenidis, Michael Stumm, Livio Soares
    In ACM Transactions on Computer Systems (TOCS) [2007, Volume 25, Issue 3]

  • Managing Shared L2 Caches on Multicore Systems in Software
  • David Tam, Reza Azimi, Livio Soares, and Michael Stumm
    Workshop on the Interaction between Operating Systems and Computer Architecture (WIOSCA 2007) [Held with ISCA-2007]

  • Experiences Understanding Performance in a Commercial Scale-Out Environment
  • Robert W. Wisniewski, Reza Azimi, Mathieu Desnoyers, Maged M. Michael, Jose Moreira, Doron Shiloach, and Livio Soares
    In European Conference on Parallel Computing (Euro-Par 2007)

• 2004
  • KFS: Exploring Flexibility in File System Design
  • Dilma Da Silva, Livio Soares, and Orran Krieger
    In the Brazilian Workshop on Operating Systems (WSO'2004)
    It is also available on the K42 web page here

  • (Poster, ps.gz) Meta-data Snapshotting: The Quest for File System Consistency
  • Livio Soares, Orran Krieger, Dilma Da Silva
    In the Poster Session of the 19th SOSP

• 2003
  • Meta-data Snapshotting: A Simple Mechanism for File System Consistency
  • Livio Soares, Orran Krieger, Dilma Da Silva
    In International Workshop on Storage Network Architecture and Parallel I/O (SNAPI '03) [Held with PACT-2003]
    It is also available on the K42 web page here, and on the SNAPI pageA here.
    
    • We propose meta-data snapshotting, a new, low overhead, technique for maintaining file-system meta-data consistency. The main idea consists of continually snapshotting the meta-data hierarchy through "copy-on-write". The technique is considerably simpler than soft-updates, and performs better than journalling. The paper describes our Linux implementation using the K42 file system, and performance comparisons with "ext3" journalled file system.

• Master's Thesis (in Portuguese):
  • Flexibilidade em um Sistema de Arquivos Componentizado (Flexibility in a Component-based File System)
  • Livio Soares
    Thesis presented to the University of São Paulo as requirement for my Master's of Science in Computer Science
    Advisor: Dilma Da Silva.