Assigning Compute Units to SLRs - 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

Currently, Xilinx devices on Data Center accelerator cards use stacked silicon consisting of several Super Logic Regions (SLRs) to provide device resources, including global memory. For best performance, when assigning ports to global memory banks, as described in Mapping Kernel Ports to Memory, it is best that the CU instance is assigned to the same SLR as the global memory it is connected to. In this case, you will want to manually assign the kernel instance, or CU into the same SLR as the global memory to ensure the best performance.

Important: If your kernel is too large to fit into a single SLR, the Vitis compiler automatically places the logic across multiple SLRs. In this case you should not assign the SLR or this could result in an error during implementation.

A CU can be assigned to an SLR using the connectivity.slr option in a config file. The syntax of the connectivity.slr option in the config file is as follows:

[connectivity]
#slr=<compute_unit_name>:<slr_ID>
slr=vadd_1:SLR2
slr=vadd_2:SLR3

Where:

  • <compute_unit_name> is an instance name of the CU as determined by the connectivity.nk option, described in Creating Multiple Instances of a Kernel, or is simply <kernel_name>_1 if multiple CUs are not specified.
  • <slr_ID> is the SLR number to which the CU is assigned, in the form SLR0, SLR1,...

The assignment of a CU to an SLR must be specified for each CU separately, but is not required. If an assigned CU is connected to global memory located in another SLR, the tool will automatically insert SLR crossing registers to help with timing closure. In the absence of an SLR assignment, the v++ linker is free to assign the CU to any SLR.

After editing the config file to include the SLR assignments, you can use it during the v++ linking process by specifying the config file using the --config option:
v++ -l --config config_slr.cfg ...