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From: "Varghese, Vipin" <vipin.varghese@intel.com>
To: "Yigit, Ferruh" <ferruh.yigit@intel.com>, Thomas Monjalon
<thomas@monjalon.net>, "Mcnamara, John" <john.mcnamara@intel.com>,
"Kovacevic, Marko" <marko.kovacevic@intel.com>
CC: "dev@dpdk.org" <dev@dpdk.org>, "stable@dpdk.org" <stable@dpdk.org>, "Tom
Barbette" <barbette@kth.se>, Yongseok Koh <yskoh@mellanox.com>, "Ananyev,
Konstantin" <konstantin.ananyev@intel.com>, "Richardson, Bruce"
<bruce.richardson@intel.com>
Thread-Topic: [PATCH v4] mk: fix scope of disabling AVX512F support
Thread-Index: AQHUpqkLGcoiCOECuUav7dZCJuUywKWkvLTw
Date: Tue, 8 Jan 2019 03:50:30 +0000
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Subject: Re: [dpdk-dev] [PATCH v4] mk: fix scope of disabling AVX512F support
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=20
diff --git a/doc/guides/rel_notes/known_issues.rst b/doc/guides/rel_notes/k=
nown_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
=20
**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 opt=
ion 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 report=
ed to cause a performance
+ drop.
+
+ On DPDK v19.02 ``AVX-512`` disable scope reduced to ``GCC`` and ``binut=
ils 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=3D97
+ https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D88096
+
+**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.
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D
=20
+* ``AVX-512`` support has been disabled for ``GCC`` builds when=20
+``binutils 2.30``
+ is detected [1] because of a crash [2]. This can affect ``native``=20
+machine type
+ build targets on the platforms that support ``AVX512F`` like ``Intel=20
+Skylake``
+ processors, and can cause a possible performance drop. The immediate=20
+workaround
+ is to use ``clang`` compiler on these platforms.
+ Initial workaround in DPDK v18.11 was to disable ``AVX-512`` support=20
+for ``GCC``
+ completely, but based on information on defect submitted to GCC=20
+community [3],
+ issue has been identified as ``binutils 2.30`` issue. Since currently=20
+only GCC
+ generates ``AVX-512`` instructions, scope limited to ``GCC`` and=20
+``binutils 2.30``
+
+ - [1]: Commit ("mk: fix scope of disabling AVX512F support")
+ - [2]: https://bugs.dpdk.org/show_bug.cgi?id=3D97
+ - [3]: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D88096
=20
Sharing ACK for documentation and update in release notes
Acked-by: Vipin Varghese <Vipin.varghese@intel.com>