doc: announce disabling GCC AVX512F as known issue

Document that AVX512F has been disabled for GCC builds [1] and document
its potential implications on release notes, known issue section.

[1]
Commit 8d07c82b239f ("mk: disable gcc AVX512F support")

Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
Acked-by: John McNamara <john.mcnamara@intel.com>

diff --git a/doc/guides/rel_notes/release_18_11.rst b/doc/guides/rel_notes/release_18_11.rst
index f66ade2..0c91c75 100644 (file)
--- a/doc/guides/rel_notes/release_18_11.rst
+++ b/doc/guides/rel_notes/release_18_11.rst
@@ -584,6 +584,17 @@ Known Issues
 
 * IBM Power8 is not supported by this release of DPDK. IBM Power9 is supported.
 
+* ``AVX-512`` support has been disabled for ``GCC`` builds [1] because of a crash [2].
+  This can affect ``native`` machine type build targets on the platforms that support
+  ``AVX512F`` like ``Intel Skylake`` processors, and can cause a possible performance drop.
+  The immediate workaround is to use ``clang`` compiler on these platforms.
+  Issue has been identified as a GCC defect and reported to GCC community [3]. Further
+  actions will be taken based on the GCC defect result.
+
+  [1]: Commit 8d07c82b239f ("mk: disable gcc AVX512F support")
+  [2]: https://bugs.dpdk.org/show_bug.cgi?id=97
+  [3]: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88096
+
 
 Tested Platforms
 ----------------