Cited by 211Parallel Computing and Optimization TechniquesComputer Graphics and Visualization TechniquesEmbedded Systems Design Techniques

An auto-tuning framework for parallel multicore stencil computations

Open access
Kamil, Shoaib, Chan, Cy, Oliker, Leonid, Shalf, John, Williams, Samuel·2010·2010 IEEE International Symposium on Parallel & Distributed Processing (IPDPS)

Abstract

Although stencil auto-tuning has shown tremendous potential in effectively utilizing architectural resources, it has hitherto been limited to single kernel instantiations; in addition, the large variety of stencil kernels used in practice makes this computation pattern difficult to assemble into a library. This work presents a stencil auto-tuning framework that significantly advances programmer productivity by automatically converting a straightforward sequential Fortran 95 stencil expression into tuned parallel implementations in Fortran, C, or CUDA, thus allowing performance portability across diverse computer architectures, including the AMD Barcelona, Intel Nehalem, Sun Victoria Falls, and the latest NVIDIA GPUs. Results show that our generalized methodology delivers significant performance gains of up to 22× speedup over the reference serial implementation. Overall we demonstrate that such domain-specific auto-tuners hold enormous promise for architectural efficiency, programmer productivity, performance portability, and algorithmic adaptability on existing and emerging multicore systems.

Integrity signals

Registry

Crossref · 10.1109/ipdps.2010.5470421

Cites

30 of 30 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

2 of 7 cited sources checked · 1 supported · 0 flagged · accuracy not yet measured

  • Premisereasoning

    Building a static auto-tuning library in the spirit of ATLAS or OSKI to implement the many different stencil kernels is infeasible.

    “Thus, building a static auto-tuning library in the spirit of ATLAS [25] or OSKI [24] to implement the many different stencil kernels is infeasible.”
    Quote in the paperSubstantial claim1 of 2 sources checked
    • cites [25] 25. R. C. Whaley, A. Petitet, and J. Dongarra. Automated Empirical Optimization of Software and the ATLAS project. Parallel Computing, 27(1-2):3-35, 2001. source
    • cites [24] 24. R. Vuduc, J. Demmel, and K. Yelick. OSKI: A library of automatically tuned sparse matrix kernels. In Proc. of SciDAC 2005, J. of Physics: Conference Series, June 2005. source
  • Findingown data

    The framework's auto-parallelization slightly improves Barcelona's performance compared to the OpenMP version.

    “Furthermore, our approach slightly improves Barcelona's performance, while Nehalem and Victoria Falls see up to a 17% and 25% speedup (respectively) compared to the OpenMP version”
    Quote in the paperNot a substantial claim
  • Findingown data

    The framework's NUMA-aware auto-parallelization performance is well correlated with the OpenMP parallelized version.

    “Results, shown as yellow diamonds in Figure 4, show that performance is well correlated with our framework's NUMA-aware autoparallelization.”
    Quote in the paperSubstantial claim
  • Findingown data

    Nehalem sees up to a 17% speedup compared to the OpenMP version.

    “Furthermore, our approach slightly improves Barcelona's performance, while Nehalem and Victoria Falls see up to a 17% and 25% speedup (respectively) compared to the OpenMP version”
    Quote in the paperSubstantial claim
  • Findingown data

    The generalized methodology delivers performance gains of up to 22× speedup over the reference serial implementation.

    “Results show that our generalized methodology delivers significant performance gains of up to 22× speedup over the reference serial implementation.”
    • Also stated in: § I. Introduction · plain
      “Results show that our generalized methodology can deliver significant performance gains of up to 22× speedup compared with the reference serial version, while allowing portability across diverse CMP technologies.”
    Quote in the paperSubstantial claim
  • May combine two claims. 15
  • The quote only partly states this claim. 2
  • Classified as probably not a substantial claim. 8
  • May combine two claims.

    Premisecitation

    Cache blocking in the unit-stride dimension could be practical on the Victoria Falls architecture, while on Barcelona or Nehalem the presence of hardware prefetchers makes such a transformation non-beneficial.

    “For example, cache blocking in the unit stride dimension could be practical on the Victoria Falls architecture, while on Barcelona or Nehalem, the presence of hardware prefetchers makes such a transformation non-beneficial [5].”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [5] 5. Kaushik Datta, Shoaib Kamil, Samuel Williams, Leonid Oliker, John Shalf, and Katherine Yelick. Optimization and perfor- mance modeling of stencil computations on modern micropro- cessors. SIAM Review, 51(1):129-159, 2009. source

      Section 4.1 says hardware prefetching can interfere with cache blocking, and section 7.1 reports better performance when the unit-stride dimension was left uncut. The paper does not establish the claimed contrast between Victoria Falls and Barcelona or Nehalem; section 2.3 identifies its studied processors as Itanium2, Opteron, Power5, and Cell. No page numbers are available in our copy. (LLM, conf=0.88)

      Experimental — accuracy not yet measured
  • May combine two claims.

    Findingreasoning

    The three examined kernels (3D Laplacian, Divergence, Gradient) have low arithmetic intensity and are expected to be memory-bandwidth bound.

    “As described below, these kernels have such low arithmetic intensity that they are expected to be memory-bandwidth bound, and thus deliver performance approximately equal to the product of their arithmetic intensity -defined as the ratio of arithmetic operations to memory traffic -and the system stream bandwidth.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingown data

    The framework's transformations yield code that outperforms compiler-only optimized versions, showing that compiler algorithms cannot always prove that these safe optimizations are allowed.

    “Additionally, the fact that our framework's transformations yield code that outperforms compileronly optimized versions shows compiler algorithms cannot always prove that these (safe) optimizations are allowed.”
    Quote in the paperSubstantial claim
  • May combine two claims. The quote only partly states this claim.

    Findingown data

    The naive arithmetic intensities of the three examined kernels range from 0.20 to 0.08, and their tuned arithmetic intensities range from 0.33 to 0.11.

    “A naïve implementation will produce memory traffic equal to the sum of these components, and will therefore result in the shown arithmetic intensity ( totalf lops totalbytes ), ranging from 0.20-0.08.”
    • Also stated in: § A. Benchmark Kernels · plain
      “Moreover, note that the kernel's auto-tuned arithmetic intensity will vary substantially from each other, ranging from 0.33-0.11.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingreasoning

    Auto-tuning is expected to provide performance boosts of 1.66×, 1.40×, and 1.28× for the Laplacian, Divergence, and Gradient kernels respectively.

    “Thus, we can also bound the resultant potential performance boost from auto-tuning per kernel -1.66×, 1.40×, and 1.28× for the Laplacian, Divergence, and Gradient respectively.”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: Auto-tuning benefit is estimated assuming a memory-bound kernel without conflict misses.
  • May combine two claims.

    Findingnone given

    The framework requires only a few minutes of human effort to instrument each stencil code, and the resulting code achieves performance comparable to previous hand-optimized code that required several months of work.

    “Furthermore, while our framework only requires a few minutes of human effort to instrument each stencil code, the resulting code achieves performance comparable to previous hand-optimized code that required several months of tedious work to produce.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingown data

    On the GTX280, previous hand-tuned Laplacian results attained 36 GFlop/s compared with the framework's 13 GFlop/s.

    “A significant disparity is seen on the GTX280, where previous handtuned Laplacian results attained 36 GFlop/s, compared with our framework's 13 GFlop/s.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingown data

    If system power is included, the GTX280's advantage is diminished and the Nehalem becomes the most power efficient architecture evaluated in this study.

    “but if system power is included, the GTX280's advantage is diminished and the Nehalem becomes the most power efficient architecture evaluated in this study.”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Findingown data

    Auto-tuning on Victoria Falls increases performance by 2.5× and 1.4× on 64 and 128 threads respectively compared to the conventional parallelized case.

    “enabling much better scalability and increasing performance by 2.5× and 1.4× on 64 and 128 threads respectively in comparison to the conventional parallelized case”
    Quote in the paperSubstantial claim
  • Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing), S4 (based).

    Interpretationnone given

    The evaluated node architectures, although diverse, most accurately represent building-blocks of current and future ultrascale supercomputing systems.

    “Although the node architectures are diverse, most accurately represent building-blocks of current and future ultrascale supercomputing systems.”
    Quote in the paperNot a substantial claim
  • Classified as probably not a substantial claim.

    Interpretationnone given

    The restricted domain allows the framework to make certain assumptions about aliasing and dependencies.

    “Our restricted domain allows us to make certain assumptions about aliasing and dependencies.”
    Quote in the paperSubstantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductcitation

    The impact of host transfer overhead is not considered in this evaluation.

    “We do not consider the impact of host transfer overhead; previous work [3] examined this potentially significant bottleneck in detail.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [3] 3. K. Datta, M. Murphy, V. Volkov, et al. Stencil Computation Optimization and Auto-Tuning on State-of-the-art Multicore Architectures. In Proceedings of SC '08, Austin, Texas, 2008. source
  • May combine two claims.

    Interpretationreasoning

    The framework side-steps the complex task of analysis and presents a simple, uniform, and familiar interface for expressing stencil kernels as a conventional Fortran expression.

    “The framework side-steps the complex task of analysis and presents a simple, uniform, and familiar interface for expressing stencil kernels as a conventional Fortran expressionwhile presenting a proof-of-concept for other potential classes of domain-specific generalized auto-tuners.”
    Quote in the paperSubstantial claim
  • May combine two claims. The quote only partly states this claim.

    Interpretationnone given

    The framework takes a straightforward sequential Fortran 95 stencil expression as input and automatically generates tuned parallel implementations in Fortran, C, or CUDA, providing performance portability across diverse architectures including AMD Barcelona, Intel Nehalem, Sun Victoria Falls, and NVIDIA GPUs.

    “Our framework takes as input a straightforward sequential Fortran 95 stencil expression and automatically generates tuned parallel implementations in Fortran, C, or CUDA, thus providing performance portability across diverse architectures that range from conventional multicore processors to some of the latest graphics processing units (GPUs).”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Interpretationreasoning

    All evaluated architectures have Flop:DRAM byte ratios significantly greater than the arithmetic intensities of the kernels, so all architectures are expected to be memory bound.

    “As all architectures have Flop:DRAM byte ratios significantly greater than the arithmetic intensities described in Section III-A, we expect all architectures to be memory bound.”
    Quote in the paperSubstantial claim
  • Classified as probably not a substantial claim.

    Interpretationreasoning

    Because optimizations are expressed as transformations on the AST, it is possible to combine them in ways that would otherwise be difficult using simple string substitution.

    “Because optimizations are expressed as transformations on the AST, it is possible to combine them in ways that would otherwise be difficult using simple string substitution.”
    Quote in the paperSubstantial claim
  • Probably not a substantial claim: may not pass S4 (based). May combine two claims.

    Interpretationnone given

    The framework has the applicability of a general domain-specific compiler like SPIRAL, while supporting multiple backend architectures.

    “In particular, the framework has the applicability of a general domain-specific compiler like SPIRAL, while supporting multiple backend architectures.”
    Quote in the paperNot a substantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationnone given

    The auto-tuning system currently handles a specific class of stencil kernels of certain dimensionality and code structure.

    “Currently, the auto-tuning system handles a specific class of stencil kernels of certain dimensionality and code structure.”
    Quote in the paperNot a substantial claim
    • The authors state this as an assumption: The auto-tuning system assumes a 2D or 3D rectahedral grid, and a stencil based on arithmetic operations and table lookups.
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationnone given

    The modular architecture of the framework enables it to be extended through the development of additional parser, strategy engine, and code generator modules.

    “The modular architecture of our framework enables it to be extended through the development of additional parser, strategy engine, and code generator modules.”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Interpretationown data

    For the CUDA implementations, the automated version only utilizes optimizations and code structures applicable to general stencils, while the hand-tuned version explicitly discovered and exploited the temporal locality specific to the Laplacian kernel, thus maximizing performance but limiting the method's applicability.

    “For the CUDA implementations, our automated version only utilizes optimizations and code structures applicable to general stencils, while the hand-tuned version explicitly discovered and exploited the temporal locality specific to the Laplacian kernel -thus maximizing performance, but limiting the method's applicability.”
    Quote in the paperSubstantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationreasoning

    The GTX280's highest performance is due to its massive parallelism at high clock rates.

    “due to its massive parallelism at high clock rates”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Study design and conductcitation

    Transfer times from system DRAM to board memory through the PCI Express bus are not included and could significantly impact performance.

    “but transfer times from system DRAM to board memory through the PCI Express bus are not included and could significantly impact performance [3].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [3] 3. K. Datta, M. Murphy, V. Volkov, et al. Stencil Computation Optimization and Auto-Tuning on State-of-the-art Multicore Architectures. In Proceedings of SC '08, Austin, Texas, 2008. source
22 of 22
  • The authors state this as an assumption.

    The auto-tuning system assumes a 2D or 3D rectahedral grid, and a stencil based on arithmetic operations and table lookups.

    “In particular, the auto-tuning system assumes a 2D or 3D rectahedral grid, and a stencil based on arithmetic operations and table lookups (array accesses).”
  • The authors state this as an assumption.

    Auto-tuning benefit is estimated assuming a memory-bound kernel without conflict misses.

    “Auto-tuning benefit is a reasonable estimate based on the improvement in arithmetic intensity assuming a memory bound kernel without conflict misses.”
  • The authors state this as an assumption.

    Capacity misses represent a reasonable estimate for cache-based superscalar processors.

    “Capacity misses represent a reasonable estimate for cache-based superscalar processors.”
  • The paper relies on this without support.

    The test harness with random data populating the grids measures performance representative of real applications.

    “the test harness simply calls the kernel with random data populating the grids and measures performance.”
  • The authors state this as an assumption.

    All kernels are memory bound and do not suffer from an abundance of capacity misses.

    “Assuming all kernels are memory bound and do not suffer from an abundance of capacity misses”
5 of 5

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Current dimensionality limit conflicts with an arbitrary-dimensionality claim

    Minor

    The paper says the implemented serial optimizations handle stencil kernels of arbitrary dimensionality, but elsewhere says the current auto-tuning system accepts only 2D or 3D grids and treats arbitrary dimensionality as future work.

1 of 1

Cites

Flagged first, then by citations

1 of the 31 references couldn’t be matched to a known paper.

Research works printed but not linked: 5

  1. 0, GreenFlash
  2. 0, Lapack&#x2014 Linear Algebra Package
  3. 0, LLVM Homepage
  4. 0, Embeddable Common Lisp
  5. 0, OpenMP API Specification for Parallel Programming

Cited by

Sorted by citations

Authors
Kamil, S., Chan, C., Oliker, L., Shalf, J., & Williams, S.
Affiliations
Lawrence Berkeley National Laboratory (US)
Venue
2010 IEEE International Symposium on Parallel & Distributed Processing (IPDPS)
Publisher
IEEE
Published
2010
Pages
1-12
ISSN
1530-2075 (ISSN-L)
OpenAlex
W2135682468
Cited by
209
References
31
Citations by year
2026: 2 · 2025: 1 · 2024: 1 · 2023: 1 · 2022: 6 · 2021: 8 · 2020: 5 · 2019: 11 · 2018: 14 · 2017: 16 · 2016: 24 · 2015: 18 · 2014: 27 · 2013: 22 · 2012: 22
FWCI
14.35
Type
conference paper
Language
en
Open access
Locations
  • IEEE International Parallel and Distributed Processing Symposium (IPDPS) (publishedVersion)
  • eScholarship (California Digital Library) (submittedVersion)
Funders
Nvidia
Topics
  • Physical Sciences › Computer Science › Hardware and Architecture › Parallel Computing and Optimization Techniques
  • Physical Sciences › Computer Science › Computer Graphics and Computer-Aided Design › Computer Graphics and Visualization Techniques
  • Physical Sciences › Computer Science › Hardware and Architecture › Embedded Systems Design Techniques
Keywords
stencil computations, auto-tuning, multi-core processors, GPU computing, CUDA, Fortran, performance portability

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