A soft real-time implementation of the Processing Graph Method (PGM) on top of LITMUS^RT
This project aims to create a soft real-time implementation of the U.S. Navy's Processing Graph Method (PGM). It can run on any POSIX-compatible system, but PGM^RT also includes optimizations to run on top of LITMUS^RT---a real-time patch to the Linux kernel [1].
Recent work by C. Liu and J. Anderson developed methods for global scheduling of graph-based real-time applications on multiprocessors [2]. They showed that soft real-time guarantees (bounded deadline tardiness) can be made with no utilization loss. That is, a multiprocessor system can be fully loaded with work while ensuring that no processing deadline is missed by more than a bounded (predictable) amount.
Graph-based workloads can be found in pipelined software architectures. Such architectures are very common to multimedia processing. For example, image and audio encoding/decoding are often processed by a series of filters. These pipelines often split into parallel pipelines only to be joined at a later stage. Therefore, general graph-based support is necessary instead of a serial pipeline model. Soft real-time guarantees for these workloads are clearly desirable, but are not realized due to a lack of operating system support.
[1] LITMUS^RT: http://www.litmus-rt.org
on github: https://github.com/LITMUS-RT/litmus-rt
[2] C. Liu and J. H. Anderson, "Supporting Soft Real-Time DAG-based Systems on Multiprocessors with No Utilization Loss", Proceedings of the 31st IEEE Real-Time Systems Symposium, pp. 3-13, December 2010.
available here: http://www.cs.unc.edu/~anderson/papers/rtss10b.pdf
PGM^RT supports POSIX-compatible systems. However, better performance for real-time scheduling can be achieved by using the LITMUS^RT Linux kernel.
To enable LITMUS^RT support, uncomment 'flags-litmus' line in the Makefile.
You must patch LITMUS^RT (version 2013.1) to support PGM^RT. Source code is available here: http://wiki.litmus-rt.org/litmus/Publications
G. Elliott, N. Kim, J. Erickson, C. Liu, and J. Anderson, "Response-Time Minimization of Automotive-Inspired Dataflows on Multicore Platforms", Proceedings of the 20th IEEE International Conference on Embedded and Real-Time Computing Systems and Applications, August 2014.
available here: http://www.cs.unc.edu/~anderson/papers/rtcsa14b_long.pdf
PGM^RT is released under the Revised BSD License:
Copyright (c) 2014, Glenn Elliott All rights reserved.
Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
Neither the name of the PGM^RT nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL GLENN ELLIOTT BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.