AVX512 was disabled for GCC because of Bugzilla issue 97 [1], the GCC defect submitted for the issue [2] highlighted that this is a known binutils version 2.30 issue.
Narrowed the scope of no-avx512 to the this specific binutils version. [1] https://bugs.dpdk.org/show_bug.cgi?id=97 [2] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88096 Fixes: 8d07c82b239f ("mk: disable gcc AVX512F support") Cc: sta...@dpdk.org Signed-off-by: Ferruh Yigit <ferruh.yi...@intel.com> --- Cc: Tom Barbette <barbe...@kth.se> Cc: Thomas Monjalon <tho...@monjalon.net> Cc: Yongseok Koh <ys...@mellanox.com> Cc: Konstantin Ananyev <konstantin.anan...@intel.com> Cc: Bruce Richardson <bruce.richard...@intel.com> v2: * Added warning message (print only once for eal) * Moved decision details to compat file, kept execution in cpuflags v3: * replace 'ld' with '$(LD)' for cross build * added meson support v4: * Document this limitation in release notes Cc: Vipin Varghese <vipin.vargh...@intel.com> --- config/meson.build | 8 ++++++ doc/guides/rel_notes/known_issues.rst | 32 ++++++++++++++++++++++++ doc/guides/rel_notes/release_19_02.rst | 13 ++++++++++ mk/rte.cpuflags.mk | 4 +-- mk/toolchain/gcc/rte.toolchain-compat.mk | 10 ++++++++ 5 files changed, 65 insertions(+), 2 deletions(-) diff --git a/config/meson.build b/config/meson.build index db32499b3..40802fc88 100644 --- a/config/meson.build +++ b/config/meson.build @@ -43,6 +43,14 @@ toolchain = cc.get_id() dpdk_conf.set_quoted('RTE_TOOLCHAIN', toolchain) dpdk_conf.set('RTE_TOOLCHAIN_' + toolchain.to_upper(), 1) +# get binutils version for the workaround of Bug 97 +ldver = run_command('ld', '-v').stdout().strip() +if ldver.contains('2.30') + if cc.has_argument('-mno-avx512f') + machine_args += '-mno-avx512f' + endif +endif + add_project_link_arguments('-Wl,--no-as-needed', language: 'c') dpdk_extra_ldflags += '-Wl,--no-as-needed' 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 Tested Platforms ---------------- diff --git a/mk/rte.cpuflags.mk b/mk/rte.cpuflags.mk index c3291b17a..541211c61 100644 --- a/mk/rte.cpuflags.mk +++ b/mk/rte.cpuflags.mk @@ -69,8 +69,8 @@ ifneq ($(filter $(AUTO_CPUFLAGS),__AVX512F__),) ifeq ($(CONFIG_RTE_ENABLE_AVX512),y) CPUFLAGS += AVX512F else -# disable AVX512F support of gcc as a workaround for Bug 97 -ifeq ($(CONFIG_RTE_TOOLCHAIN_GCC),y) +# disable AVX512F support for GCC & binutils 2.30 as a workaround for Bug 97 +ifeq ($(FORCE_DISABLE_AVX512),y) MACHINE_CFLAGS += -mno-avx512f endif endif diff --git a/mk/toolchain/gcc/rte.toolchain-compat.mk b/mk/toolchain/gcc/rte.toolchain-compat.mk index 44904295c..33ea3f03a 100644 --- a/mk/toolchain/gcc/rte.toolchain-compat.mk +++ b/mk/toolchain/gcc/rte.toolchain-compat.mk @@ -20,6 +20,16 @@ HOST_GCC_MINOR = $(shell echo __GNUC_MINOR__ | $(HOSTCC) -E -x c - | tail -n 1) HOST_GCC_PATCHLEVEL = $(shell echo __GNUC_PATCHLEVEL__ | $(HOSTCC) -E -x c - | tail -n 1) HOST_GCC_VERSION = $(HOST_GCC_MAJOR)$(HOST_GCC_MINOR) +LD_VERSION = $(shell $(LD) -v) +# disable AVX512F support for GCC & binutils 2.30 as a workaround for Bug 97 +ifneq ($(filter 2.30%,$(LD_VERSION)),) +FORCE_DISABLE_AVX512 := y +# print warning only once for librte_eal +ifneq ($(filter %librte_eal,$(lastword $(CURDIR))),) +$(warning AVX512 support disabled because of ld 2.30. See Bug 97) +endif +endif + # if GCC is older than 4.x ifeq ($(shell test $(GCC_VERSION) -lt 40 && echo 1), 1) MACHINE_CFLAGS = -- 2.17.2
