Version : Intel® C++ Compiler Version 11.0 and Version 12.0
Operating System : Windows*, Linux*, Mac OS* X
Problem Description : When the STREAM component of the HPCC benchmark suite is built with with version 11 of the Intel C++ compiler, the performance may be about 20% less than when it is built using version 10.1, for some choices of command line options. Typical options on Linux might be:
-O3 -xsse4.1 -ansi-alias -ip -opt-streaming-stores always for 11.0, or
-O3 -xS -ansi-alias -ip -opt-streaming-stores always for 10.1.
This is because streaming store instructions (non-temporal stores that bypass the cache) are not generated for certain inlined functions with the 11.0 compiler.
In the 12.0 compiler, from the release through update 3, a similar slowdown may be seen for just the COPY component of STREAM, including for the standalone version.
Resolution Status : This is a known issue that is resolved in compiler update 11.0.081 and later. Directions on how to download a specific release are described here.
The issue with the COPY component of stream is fixed in update 4 to the 12.0 compiler.
The original issue may be worked around for 11.0 versions before 11.0.081 by disabling inlining for this benchmark. On Linux, for example, this may be done with -fno-inline.
The issue with early versions of the 12.0 compiler may be worked around in a similar way. For example, for the C compiler, use -ffreestanding (Linux or Mac OS X) or /Qfreestanding (Windows), or for the Fortran compiler, use -nolib-inline (Linux or Mac OS) or /Oi- (Windows).
Note that the use of -opt-streaming-stores always (Linux or Mac OS X) or /Qopt-streaming-stores:always (Windows) is recommended for building all versions of the STREAM benchmark.
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