Reliable Many-Core Programming

Lead Research Organisation: Imperial College London
Department Name: Dept of Computing

Abstract

The computational demands of modern computer applications make the
pursuit of high performance more critical than ever, and mobile,
battery-powered devices, as well as concerns related to climate
change, require high performance to co-exist with energy-efficiency.
Due to physical limits, the traditional means for improving hardware
performance by increasing processor frequency now carries an
unacceptably high energy cost. Advances in processor fabrication
technology instead allow the construction of many-core processors,
where hundreds or thousands of processing elements are placed on a
single chip, promising high performance and energy-efficiency through
sheer volume of processing elements.

Many-core devices are present in practically all consumer devices,
including smartphones and tablets. As a result, the general public in
developed countries interact with many-core software daily. Many-core
technology is also used to accelerate safety-critical software in
domains such as medical imaging and autonomous vehicle navigation.

It is thus important that many-core software should be reliable. This
requires reliable software from programmers, but also a reliable
"stack" to support this software, including compilers that allow
software to execute on many-core devices, and the many-core devices
themselves. Recent work on formal verification and testing by myself
and other researchers has identified serious technical problems
spanning the many-core stack. These problems undermine confidence in
applications of many-core technology: defective many-core software
could risk fatal accidents in critical domains, and impact negatively
on users in other important application areas.

My long-term vision is that the reliability of many-core programming
can be transformed through breakthroughs in programming language
specification, formal verification and test case generation, enabling
automated tools to assist programmers and platform vendors in
constructing reliable many-core applications and language
implementations. The aim of this five-year Fellowship is to undertake
foundational research to investigate a number of open problems whose
solution is key to enabling this long-term vision.

First, I seek to investigate whether it is possible to precisely
express the intricacies of many-core programming language using formal
mathematics, providing a rigorous basis on which software and language
implementations can be constructed.

Second, I aim to tackle several open problems that stand in the way of
effective formal verification of many-core software, which would allow
developers to obtain strong guarantees that such software will operate
as required.

Third, I will investigate raising this level of rigour beyond
many-core languages. A growing trend is for applications to be written
in relatively simple, high-level representations, and then
automatically translated into high-performance many-core code. This
translation process must preserve the meaning of programs; I will
investigate methods for formally certifying that it does.

Fourth, I will formulate new methods for testing many-core language
implementations, exploiting the rigorous language definitions brought
by my approach to enable high test coverage of subtle language
features.

Collectively, progress on these problems promises to enable a
*high-assurance* many-core stack. I will demonstrate one instance of
such a stack for the industry-standard OpenCL language and the PENCIL
high-level language, showing that high-level PENCIL programs can be
reliably compiled into rigorously-defined OpenCL, integrated with
verified library components, and deployed on thoroughly tested
implementations from many-core vendors.

Partnership with four leading many-core technology vendors, AMD, ARM,
Imagination Technologies and NVIDIA, provides excellent opportunities
for the advances the Fellowship makes to have broad industrial impact.

Planned Impact

The project has a large set of potential beneficiaries. The ultimate
beneficiaries of my long-term vision for reliable many-core
programming are end-users of software that employs many-core
acceleration. Because many-core hardware now ships with practically
all desktop, laptop and mobile devices, society is starting to
interact with many-core software on a daily basis. By leading to
improvements in the robustness of this software, and the platforms on
which it operates, my proposed project offers significant societal
benefit. Many-core technology is increasingly employed in
safety-critical contexts, for example it has found application in
medical imaging, pedestrian detection, and autonomous navigation for
self-driving cars. Reliability improvements in these areas offer to
make society safer. The rise of many-core technology also presents
new attack vectors that pose cyber-security and cyber-terrorism risks;
the advanced reasoning techniques that my research will bring will
allow many-core software to be rigorously engineered to defend against
these threats.

The fundamental advances made during the project will have long-term
academic impact, yielding results that researchers in several fields
can exploit. See the "Academic Beneficiaries" form for more details.

My Fellowship has very high potential for industrial impact.
Many-core platform vendors, including my project partners AMD, ARM,
Imagination Technologies and NVIDIA and several other companies, will
be able to exploit the Fellowship research to improve many-core
language implementations, increasing their market value. There is
potential for commercial exploitation of the research outcomes by tool
providers, and the wide range of software developers who apply
many-core acceleration in diverse domains will be able to build more
reliable software using the advanced analyses the Fellowship will
bring. All these stakeholders will benefit from the transformation in
the rigour of many-core programming language design offered by my
approach. Specifically, the 80+ industrial contributing members of
the Khronos Group will be beneficiaries of improvements to OpenCL and
related APIs that arise from the project. The large and growing
market associated with many-core technology means that uptake by
industry has the potential to lead to corresponding economic impact.

Close collaboration with industry during the Fellowship will give rise
to industrial impact on the Fellowship partners early during the
five-year project, and my strong impact plans will help to broaden
this impact to other industrial beneficiaries during the project
lifetime, leading to widespread industrial adoption over a 5-10-year
period. This widespread adoption has the potential to transform
many-core programming, impacting on industrial practice in the long
term and benefiting society for decades to come.

Publications

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Donaldson A (2017) Automated testing of graphics shader compilers in Proceedings of the ACM on Programming Languages