Re: [dpdk-dev] [PATCH v4] mk: fix scope of disabling AVX512F support

["Varghese, Vipin" <vipin.varghese@intel.com>]

 
diff --git a/doc/guides/rel_notes/known_issues.rst b/doc/guides/rel_notes/known_issues.rst
index a1face9c1..b0057a2bc 100644
--- a/doc/guides/rel_notes/known_issues.rst
+++ b/doc/guides/rel_notes/known_issues.rst
@@ -826,3 +826,35 @@ Kernel crash when hot-unplug igb_uio device while DPDK application is running
 
 **Driver/Module**:
    ``igb_uio`` module.
+
+
+AVX-512 support disabled
+------------------------
+
+**Description**:
+   ``AVX-512`` support has been disabled on some conditions.
+   This shouldn't be confused with ``CONFIG_RTE_ENABLE_AVX512`` config option which is already
+   disabled by default. This config option defines if ``AVX-512`` specific implementations of
+   some file to be used or not. What has been disabled is compiler feature to produce ``AVX-512``
+   instructions from any source code.
+
+   On DPDK v18.11 ``AVX-512`` disabled for all ``GCC`` builds which reported to cause a performance
+   drop.
+
+   On DPDK v19.02 ``AVX-512`` disable scope reduced to ``GCC`` and ``binutils version 2.30`` based
+   on information accured from the GCC community defect.
+
+**Reason**:
+   Generated ``AVX-512`` code cause crash:
+   https://bugs.dpdk.org/show_bug.cgi?id=97
+   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88096
+
+**Resolution/Workaround**:
+   Update ``binutils`` to newer version than ``2.30``.
+   Use different compiler, like ``clang`` for this case.
+
+**Affected Environment/Platform**:
+    ``GCC`` and ``binutils version 2.30``.
+
+**Driver/Module**:
+    ALL.
diff --git a/doc/guides/rel_notes/release_19_02.rst b/doc/guides/rel_notes/release_19_02.rst
index 39c6ff826..b6322b282 100644
--- a/doc/guides/rel_notes/release_19_02.rst
+++ b/doc/guides/rel_notes/release_19_02.rst
@@ -276,6 +276,19 @@ Known Issues
    Also, make sure to start the actual text at the margin.
    =========================================================
 
+* ``AVX-512`` support has been disabled for ``GCC`` builds when 
+``binutils 2.30``
+  is detected [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.
+  Initial workaround in DPDK v18.11 was to disable ``AVX-512`` support 
+for ``GCC``
+  completely, but based on information on defect submitted to GCC 
+community [3],
+  issue has been identified as ``binutils 2.30`` issue. Since currently 
+only GCC
+  generates ``AVX-512`` instructions, scope limited to ``GCC`` and 
+``binutils 2.30``
+
+  - [1]: Commit ("mk: fix scope of disabling AVX512F support")
+  - [2]: https://bugs.dpdk.org/show_bug.cgi?id=97
+  - [3]: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88096
 
Sharing ACK for documentation and update in release notes

Acked-by: Vipin Varghese <Vipin.varghese@intel.com>