Real-time disk scheduling in a mixed-media file system

H.G.P. Bosch, Sape J. Mullender

    Research output: Contribution to conferencePaperpeer-review

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    This paper presents our real-time disk scheduler called the Delta L scheduler, which optimizes unscheduled best-effort disk requests by giving priority to best-effort disk requests while meeting real-time request deadlines. Our scheduler tries to execute real-time disk requests as much as possible in the background. Only when real-time request deadlines are endangered, our scheduler gives priority to real-time disk requests. The Delta L disk scheduler is part of our mixed-media file system called Clockwise. An essential part of our work is extensive and detailed raw disk performance measurements. The Delta L disk scheduler for its real-time schedulability analysis and to decide whether scheduling a best-effort request before a real-time request violates real-time constraints uses these raw performance measurements. Further, a Clockwise off-line simulator uses the raw performance measurements where a number of different disk schedulers are compared. We compare the Delta L scheduler with a prioritizing Latest Start Time (LST) scheduler and non-prioritizing EDF scheduler. The Delta L scheduler is comparable to LST in achieving low latencies for best-effort requests under light to moderate real-time loads and better in achieving low latencies for best-effort requests for extreme real-time loads. The simulator is calibrated to an actual Clockwise. Clockwise runs on a 200MHz Pentium-Pro based PC with PCI bus, multiple SCSI controllers and disks on Linux 2.2.x and the Nemesis kernel. Clockwise performance is dictated by the hardware: all available bandwidth can be committed to real-time streams, provided hardware overloads do not occur.
    Original languageUndefined
    Number of pages10
    Publication statusPublished - 2000
    EventSixth Real-Time Technology and Application Symposium, RTAS 2000 - Washington, United States
    Duration: 31 May 20002 Jun 2000
    Conference number: 6


    ConferenceSixth Real-Time Technology and Application Symposium, RTAS 2000
    Abbreviated titleRTAS 2000
    Country/TerritoryUnited States


    • IR-56167
    • EWI-981

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