Developer Guide

Contents

Perform Kernel Computations Using Local or Private Memory

To optimize memory access efficiency, minimize the number of global memory accesses by performing DPC++ kernel computations in local or private memory.
To minimize global memory accesses, it is often best to preload data from a group of computations from global memory to a local or private memory. Perform kernel computations on the preloaded data and write the results back to the global memory.

Preload Data into Local Memory or Private Memory

Local memory is considerably smaller than global memory, but it has significantly higher bandwidth and much lower latency. Unlike global memory accesses, the kernel can access local memory randomly without any performance penalty. When you structure your kernel code, attempt to access the global memory sequentially, and buffer that data in on-chip local memory before your kernel uses the data for computation.

Store Variables and Arrays in Private Memory

The 
Intel® oneAPI DPC++/C++ Compiler
implements private memory using FPGA registers in the kernel datapath or block RAMs. The
Intel® oneAPI DPC++/C++ Compiler
analyzes the private memory accesses and promotes them to register accesses. Scalar variables, for example
float
,
int
and
char
, are typically promoted. Aggregate data types are promoted if array-access indices are compile-time constants. Typically, private memory is useful for storing single variables or small arrays. Registers are plentiful hardware resources in FPGAs, and it is usually better to use private memory instead of other memory types whenever possible. The kernel can access private memories in parallel, allowing them to provide more bandwidth than any other memory type (global, local, and constant memories).
For more information on the implementation of private memory using registers, refer to Inferring a Shift Register.

Product and Performance Information

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Intel's compilers may or may not optimize to the same degree for non-Intel microprocessors for optimizations that are not unique to Intel microprocessors. These optimizations include SSE2, SSE3, and SSSE3 instruction sets and other optimizations. Intel does not guarantee the availability, functionality, or effectiveness of any optimization on microprocessors not manufactured by Intel. Microprocessor-dependent optimizations in this product are intended for use with Intel microprocessors. Certain optimizations not specific to Intel microarchitecture are reserverd for Intel microprocessors. Please refer to the applicable product User and Reference Guides for more information regarding the specific instruction sets covered by this notice.

Notice revision #20110804