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% [1]>linuxsymposium July 20-23rd, 2005, Ottawa, Canada
% Registration Active Block I/O Scheduling System (ABISS)
%
% [2]Register/Submit Giel de Nijs (giel.de.nijs@philips.com)
The Active Block I/O Scheduling System (ABISS) is an
extension of the hard-disk storage subsystem of Linux.
It is designed to provide guaranteed reading and
writing bitrates to applications, with minimal overhead
and low latency. The core element of ABISS is a
scheduler that performs intelligent read-ahead or
write-back, based on the access profile the application
has previously requested. An adaptation of existing
work on incorporating support for priority requests
into the elevator (``IO scheduler'') is part of our
implementation, and enables ABISS to ensure that
real-time requests are served in a timely manner.
Besides the extension to the storage subsystem, we have
implemented experimental support for delayed allocation
in the FAT file system, to be effectively able to
provide the guaranteed writing bitrates. We are working
on combining this with disk space reservations, which
are also part of on-going development on ext3.
Applications use the regular POSIX API, and control the
ABISS extensions either directly through ioctls, or a
library offering simple wrapper functions. ABISS
contains by a user-space demon that oversees resource
allocation and handles admission control. Also some
minor modifications were made to file system drivers.
ABISS currently supports FAT, VFAT, ext2, and ext3. In
a set of experimental runs with real-life data rates on
a deliberately not very powerful test system reflecting
a typical embedded device, we have measured that all
read and write operations completed within 6 ms, while
a background load of eight concurrent greedy readers or
writers, served in a best-effort way, experienced
delays worse by a factor of more than 4000.
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