SONAR Systems Research Group

The Sonar research group studies the interaction of operating systems and hardware, including devices and new processor/memory technologies.

Our research focuses on bridging the growing gap between hardware and operating systems. We seek to improve the reliability and performance of hardware access while simplifying the programmer’s task. Our work covers the major hardware in computer systems: devices, memory, storage, and the CPU.


Solid-State Storage

  • Non-Volatile Memory Technology
  • New storage technologies such as Phase-Change Memory (PCM or PCRam), Memristors, and flash promise to change how programs and operating systems interact with storage. Our research focuses on new uses for these technologies outside traditional file storage.

    Efficient Virtual Memory

    Virtual memory, while a great idea, comes at an increasing cost. Translation lookaside buffers (TLBs) consume a disproportionate amount of power (up to 13% in some modern processors) and can cause overhead exceeding 70% for some applications. We recognized that the most efficient form of translation is a segment: a set of three values (base, limit, offset) can translate an arbitrarily large range of virtual addresses to physical addresses. We first pursued this idea with Direct Segments which provides a single segment, abstracted in the operating system with a Primary Region. More recently, we have extended the direct segment design to allow an arbitrary number of segments with Range Translations Virtual memory has even higher cost in virtualized environments, common in cloud computing. We developed an extension of direct segments for use in virtual machines, where we created three designs that trade off performance, features, and compatibility with existing code. Recognizing that this approach has a cost in terms of creating contiguous memory, we also designed Agile Paging, which switches between two different memory virtualize approaches (nested and shadow paging) within a single address space to achieve performance with 2.5% of native execution.

    Reinventing Drivers

  • Device Drivers

    Device drivers are a major source of complexity, unreliability, and cost for modern operating systems. As evidence, drivers account for the majority of system crashes: Microsoft reports that 89% of Windows XP crashes are caused by device drivers, and Linux driver code had up to seven times the bug density of other kernel code. The objective of my research is to improve device drivers by (1) reducing the complexity and cost of implementing device drivers, (2) improving the fault tolerance of device drivers, and (3) improving the performance of device drivers on modern hardware and software architectures.

    Transactional Memory

  • xCalls
  • LogTM

    Transactional memory promises to simplify multhreaded programming by removing the need to associate a lock with each piece of shared data. Instead, programmers specify transactions, which forces a set of statements to execute atomically.

    One of the key problems faced by transactional memory systems is virtualization and the operating system: how can you virtualize hardware support for transactional memory, so that transactions can co-exist with paging and context switching? Also, how can you provide unbounded length transactions in the presence of limited-size hardware structures? Finally, how do system calls and I/O operate in the presence of transctions?

  • Publications

  • Complete list of publications
  • Members


  • Michael Swift

  • Current Students

  • Yan Zhai
  • Akhil Guliana
  • Mark Mansi
  • Nikhita Kunati
  • Swapnil Haria
  • Pratyush Mahapatra

  • Past Students

  • Adwait Tumbde , now at Yahoo
  • Arini Balakrishnan, now at Sun
  • Neelam Goyal , now at Oracle
  • Andres Tack , now at Skype
  • Haris Volos , now at HP Labs
  • Matthew Renzelmann , now t Microsoft
  • Mohit Saxena , now at IBM
  • Asim Kadav, now at NEC labs
  • Sankaralingam Panneerselvam, now at Facebook