Automated Roofline analysis is one of the most powerful features of Intel® Advisor. Intel Advisor now has a technical preview feature that gives Roofline recommendations and guidance to assist you with interpreting the Roofline chart.
Background
A Roofline chart is a visual representation of application performance in relation to hardware limitations, including memory bandwidth and computational peaks. It was first proposed by researchers at the University of California at Berkeley in the 2009 paper “Roofline: An Insightful Visual Performance Model for Multicore Architectures.” In 2013, this model was improved by researchers at the Technical University of Lisbon in a paper called “Cache-Aware Roofline Model: Upgrading the Loft.” Traditionally, Roofline charts have been calculated and plotted manually, but Intel® Advisor now automatically builds Roofline plots.
The Roofline provides insight into:
- Where your performance bottlenecks are
- How much performance is left on the table because of them
- Which bottlenecks are possible to address, and which ones are worth addressing
- Why these bottlenecks are most likely occurring
- What your next steps should be
Getting Roofline Guidance
Since roofline guidance is currently a technical preview feature you need set the following env variable ADVIXE_EXPERIMENTAL=roofline_guidance.
For the roofline chart below, Intel Advisor divides the chart into three distinct regions: memory bound, memory and compute bound, and compute bound.Also, by hovering over one of your circles, you can also see a vertical line with intersections on the closest and furthest roof, with the ratio comparing the circles GFLOPS with the roofs GFLOPS. Note: These features are part of the standard product and are not an experimental.
You can see loop specific guidance by click the Recommendations tab in the center of the Intel Advisor GUI.
To see a more detailed view, click on the Code Analytics tab.
Current limitations
Currently roofline guidance is actionable only for your innermost loops. Outer loops give recommendations that are totally misleading and should not be used.
Summary/Conclusions
Roofline guidance is a new and novel feature of Intel Advisor. Feature technical previews are one of the ways we gather customer feedback as we continue to improve our products. You can download the latest Intel Advisor using the following link Choose Download .
You can submit feedback at the following e-mail address: vector_advisor@intel.com