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Diffstat (limited to 'Documentation/intro')
| -rw-r--r-- | Documentation/intro/install/dpdk.rst | 30 |
1 files changed, 30 insertions, 0 deletions
diff --git a/Documentation/intro/install/dpdk.rst b/Documentation/intro/install/dpdk.rst index dbf88ec43..4d858304c 100644 --- a/Documentation/intro/install/dpdk.rst +++ b/Documentation/intro/install/dpdk.rst @@ -136,6 +136,16 @@ has to be configured to build against the DPDK library (``--with-dpdk``). While ``--with-dpdk`` is required, you can pass any other configuration option described in :ref:`general-configuring`. + It is strongly recommended to build OVS with at least ``-msse4.2`` and + ``-mpopcnt`` optimization flags. If these flags are not enabled, the AVX512 + optimized DPCLS implementation is not available in the resulting binary. + For technical details see the subtable registration code in the + ``lib/dpif-netdev-lookup.c`` file. + + An example that enables the AVX512 optimizations is:: + + $ ./configure --with-dpdk=$DPDK_BUILD CFLAGS="-Ofast -msse4.2 -mpopcnt" + #. Build and install OVS, as described in :ref:`general-building` Additional information can be found in :doc:`general`. @@ -147,6 +157,26 @@ Additional information can be found in :doc:`general`. __ https://github.com/openvswitch/ovs/blob/master/rhel/README.RHEL.rst + +Possible issues when enabling AVX512 +++++++++++++++++++++++++++++++++++++ + +The enabling of ISA optimized builds requires build-system support. +Certain versions of the assembler provided by binutils is known to have +AVX512 assembling issues. The binutils versions affected are 2.30 and 2.31. +As many distros backport fixes to previous versions of a package, checking +the version output of ``as -v`` can err on the side of disabling AVX512. To +remedy this, the OVS build system uses a build-time check to see if ``as`` +will correctly assemble the AVX512 code. The output of a good version when +running the ``./configure`` step of the build process is as follows:: + + $ checking binutils avx512 assembler checks passing... yes + +If a bug is detected in the binutils assembler, it would indicate ``no``. +Build an updated binutils, or request a backport of this binutils +fix commit ``2069ccaf8dc28ea699bd901fdd35d90613e4402a`` to fix the issue. + + Setup ----- |