Running Multiple Implementation Strategies for Timing Closure - 2021.2 English

Vitis Unified Software Platform Documentation: Application Acceleration Development (UG1393)

Document ID
UG1393
ft:locale
English (United States)
Release Date
2021-12-15
Version
2021.2 English

For challenging designs, it can take multiple iterations of Vivado implementation using multiple different strategies to achieve timing closure. This topic shows you how to launch multiple implementation strategies at the same time in the hardware build (-t hw), and how to identify and use successful runs to generate the device binary and complete the build.

As explained in --vivado Options the --vivado.impl.strategies command enables you to specify multiple strategies to run in a single build pass. The command line would look as follows:

v++ --link -s -g -t hw --platform xilinx_zcu102_base_202010_1 -I . \
--vivado.impl.strategies "Performance_Explore,Area_Explore" -o kernel.xclbin hello.xo

In the example above, the Performance_Explore and Area_Explore strategies are run simultaneously in the Vivado build to see which returns the best results. You can specify the ALL to have all available strategies run within the tool.

Important: Running ALL implementation strategies might launch 30 or more runs in the Vivado tool, including any user-defined strategies stored in your home directory (~/.Xilinx/Vivado/2021.1/strategies). This can be a tremendous drain on resources, and is not advised. You can prevent this by defining specific strategies to run, and using a command queue to distribute the process load in some managed way, such as through the --vivado.impl.jobs or the --vivado.impl.lsf commands.

You can also determine this option in a configuration file in the following form:

#Vivado Implementation Strategies
[vivado]
impl.strategies=Performance_Explore,Area_Explore

The Vitis compiler automatically picks the first completed run results that meets timing to proceed with the build process and generate the device binary. However, you can also direct the tool to wait for all runs to complete and pick the best results from the completed runs before proceeding. This would require the use of the --advanced.compiler directive as shown:

[advanced]
param=compiler.multiStrategiesWaitOnAllRuns=1

compiler.multiStrategiesWaitOnAllRuns=0 represents the default behavior. If you want v++ to wait for all runs to complete, which will get their report files, change that parameter value to 1.

As discussed in Link Summary: Multiple Strategies and Timing Reports, Vitis analyzer displays the implementation results for the all strategies that have been allowed to run to completion. This includes an overview of the implementation results, as well as a Timing Summary report. You can use this feature to review the different strategies and results.

You can also manually review the results of all implementation strategies after they have completed. Then, use the results of any of the implementation runs by using the --reuse_impl option as described in Using -to_step and Launching Vivado Interactively.