Portable inter-workgroup barrier synchronisation for GPUs

Sorensen, Tyler; Donaldson, Alastair F.; Batty, Mark; Gopalakrishnan, Ganesh; Rakamarić, Zvonimir

doi:10.1145/2983990.2984032

Cited by 19 publications

(3 citation statements)

References 26 publications

(19 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In fact, Memalloy can also be used to check libraries under weak memory. Prior work has (manually) verified that stack, queue, and barrier libraries implement their specifications under weak memory models [8,52]; here we show how checking these types of properties can be automated up to a bounded number of library and client events. We see this as a straightforward first-step towards a general verification effort.…”

Section: Checking Metatheoretical Propertiesmentioning

confidence: 86%

The semantics of transactions and weak memory in x86, Power, ARM, and C++

2018

Self Cite

View full text Add to dashboard Cite

Weak memory models provide a complex, system-centric semantics for concurrent programs, while transactional memory (TM) provides a simpler, programmer-centric semantics. Both have been studied in detail, but their combined semantics is not well understood. This is problematic because such widely-used architectures and languages as x86, Power, and C++ all support TM, and all have weak memory models. Our work aims to clarify the interplay between weak memory and TM by extending existing axiomatic weak memory models (x86, Power, ARMv8, and C++) with new rules for TM. Our formal models are backed by automated tooling that enables (1) the synthesis of tests for validating our models against existing implementations and (2) the model-checking of TM-related transformations, such as lock elision and compiling C++ transactions to hardware. A key finding is that a proposed TM extension to ARMv8 currently being considered within ARM Research is incompatible with lock elision without sacrificing portability or performance.

show abstract

Section: Checking Metatheoretical Propertiesmentioning

confidence: 86%

The semantics of transactions and weak memory in x86, Power, ARM, and C++

2018

Self Cite

View full text Add to dashboard Cite

show abstract

“…This method is not portable as the number of launched work-groups depends on the device. Sorensen et al [22] extended it to be portable by discovering work-group occupancy dynamically. Their implementation of inter work-group barrier synchronisation is useful when the developer knows there is interaction between work-groups that needs to be synchronised.…”

Section: Related Workmentioning

confidence: 99%

Automated test generation for OpenCL kernels using fuzzing and constraint solving

Peng

Rajan

2020

Proceedings of the 13th Annual Workshop on General Purpose Processing Using Graphics Processing Unit

View full text Add to dashboard Cite

Graphics Processing Units (GPUs) are massively parallel processors offering performance acceleration and energy efficiency unmatched by current processors (CPUs) in computers. These advantages along with recent advances in the programmability of GPUs have made them attractive for general-purpose computations. Despite the advances in programmability, GPU kernels are hard to code and analyse due to the high complexity of memory sharing patterns, striding patterns for memory accesses, implicit synchronisation, and combinatorial explosion of thread interleavings. Existing few techniques for testing GPU kernels use symbolic execution for test generation that incur a high overhead, have limited scalability and do not handle all data types.We propose a test generation technique for OpenCL kernels that combines mutation-based fuzzing and selective constraint solving with the goal of being fast, effective and scalable. Fuzz testing for GPU kernels has not been explored previously. Our approach for fuzz testing randomly mutates input kernel argument values with the goal of increasing branch coverage. When fuzz testing is unable to increase branch coverage with random mutations, we gather path constraints for uncovered branch conditions and invoke the Z3 constraint solver to generate tests for them.In addition to the test generator, we also present a schedule amplifier that simulates multiple work-group schedules, with which to execute each of the generated tests. The schedule amplifier is designed to help uncover inter work-group data races. We evaluate the effectiveness of the generated tests and schedule amplifier using 217 kernels from open source projects and industry standard benchmark suites measuring branch coverage and fault finding. We find our test generation technique achieves close to 100% coverage and mutation score for majority of the kernels. Overhead incurred in test generation is small (average of 0.8 seconds). We also confirmed our technique scales easily to large kernels, and can support all OpenCL data types, including complex data structures. CCS CONCEPTS• Software and its engineering → Software testing and debugging; Massively parallel systems.

show abstract

“…A problem is the synchronization of processing steps over the total amount of data, which might be much larger than the number of work items that can actually run in parallel. Sorensen et al [39] discuss these limitations and propose an inter-workgroup barrier that synchronizes all threads running in parallel by estimating the occupancy, i.e., the number of work items that can run in parallel, and building a barrier using OpenCL atomics.…”

Section: Nested Parallelismmentioning

confidence: 99%

OpenCL Actors – Adding Data Parallelism to Actor-Based Programming with CAF

Hiesgen

Charousset

Schmidt

2018

Lecture Notes in Computer Science

View full text Add to dashboard Cite

The actor model of computation has been designed for a seamless support of concurrency and distribution. However, it remains unspecific about data parallel program flows, while available processing power of modern many core hardware such as graphics processing units (GPUs) or coprocessors increases the relevance of data parallelism for general-purpose computation.In this work, we introduce OpenCL-enabled actors to the C++ Actor Framework (CAF). This offers a high level interface for accessing any OpenCL device without leaving the actor paradigm. The new type of actor is integrated into the runtime environment of CAF and gives rise to transparent message passing in distributed systems on heterogeneous hardware. Following the actor logic in CAF, OpenCL kernels can be composed while encapsulated in C++ actors, hence operate in a multi-stage fashion on data resident at the GPU. Developers are thus enabled to build complex data parallel programs from primitives without leaving the actor paradigm, nor sacrificing performance. Our evaluations on commodity GPUs, an Nvidia TESLA, and an Intel PHI reveal the expected linear scaling behavior when offloading larger workloads. For sub-second duties, the efficiency of offloading was found to largely differ between devices. Moreover, our findings indicate a negligible overhead over programming with the native OpenCL API.computing has been widely recognized as an important optimization strategy. In addition, accelerating coprocessors that better support code branching established on the market.Since not all tasks can benefit from such specialized devices, developers need to distribute work on the various architectural elements. Managing such a heterogeneous runtime environment inherently increases the complexity. While some loop-based computations can be offloaded to GPUs using OpenACC [10] or recent versions of OpenMP [15] with relatively little programming effort, it has been shown that a consistent task-oriented design exploits the available parallelism more efficiently. Corresponding results achieve better performance [27] while they are also applicable to more complex work loads. However, manually orchestrating tasks between multiple devices is an error-prone and complex task.The actor model of computation describes applications in terms of isolated software entities-actorsthat communicate by asynchronous message passing. Actors can be distributed across any number of processors or machines by the runtime system as they are not allowed to share state and thus can always be executed in parallel. The message-based decoupling of software entities further enables actors to run on different devices in a heterogeneous environment. Hence, the actor model can simplify software development by hiding the complexity of heterogeneous and distributed deployments.In this work, we take up our previous contribution [22] about actors programmed with OpenCLthe Open Computing Language standardized by the Khronos Group [41]. We enhance the integration of heterogeneous programming with the C++ ...

show abstract

Portable inter-workgroup barrier synchronisation for GPUs

Cited by 19 publications

References 26 publications

The semantics of transactions and weak memory in x86, Power, ARM, and C++

The semantics of transactions and weak memory in x86, Power, ARM, and C++

Automated test generation for OpenCL kernels using fuzzing and constraint solving

OpenCL Actors – Adding Data Parallelism to Actor-Based Programming with CAF

Contact Info

Product

Resources

About