[01/10] build: add an option to enable LTO build
diff mbox series

Message ID 20190905093239.27187-2-amo@semihalf.com
State Superseded, archived
Delegated to: Thomas Monjalon
Headers show
Series
  • Add an option to use LTO for DPDK build
Related show

Checks

Context Check Description
ci/checkpatch warning coding style issues
ci/Intel-compilation success Compilation OK
ci/iol-dpdk_compile success Compile Testing PASS
ci/iol-dpdk_compile_ovs success Compile Testing PASS
ci/iol-dpdk_compile_spdk success Compile Testing PASS
ci/intel-Performance success Performance Testing PASS
ci/mellanox-Performance success Performance Testing PASS

Commit Message

Andrzej Ostruszka Sept. 5, 2019, 9:32 a.m. UTC
This patch adds an option to enable link time optimization.  In addition
to LTO option itself (-flto) fat-lto-objects are being used.  This is
because during the build pmdinfogen scans the generated ELF objects to
find this_pmd_name* symbol in symbol table.  Without fat-lto-objects gcc
produces ELF only with extra symbols for internal use during linking and
clang does not produce ELF at all (only LLVM IR bitcode).

Signed-off-by: Andrzej Ostruszka <aostruszka@marvell.com>
---
 .travis.yml                                |  7 +++++
 config/common_base                         |  5 +++
 config/meson.build                         |  9 ++++++
 doc/guides/prog_guide/lto.rst              | 36 ++++++++++++++++++++++
 doc/guides/rel_notes/release_19_11.rst     |  8 +++++
 meson_options.txt                          |  2 ++
 mk/toolchain/clang/rte.toolchain-compat.mk |  4 +++
 mk/toolchain/clang/rte.vars.mk             |  8 +++++
 mk/toolchain/gcc/rte.toolchain-compat.mk   |  4 +++
 mk/toolchain/gcc/rte.vars.mk               | 12 ++++++++
 mk/toolchain/icc/rte.vars.mk               |  8 +++++
 11 files changed, 103 insertions(+)
 create mode 100644 doc/guides/prog_guide/lto.rst

Comments

Bruce Richardson Sept. 5, 2019, 9:36 a.m. UTC | #1
On Thu, Sep 05, 2019 at 11:32:30AM +0200, Andrzej Ostruszka wrote:
> This patch adds an option to enable link time optimization.  In addition
> to LTO option itself (-flto) fat-lto-objects are being used.  This is
> because during the build pmdinfogen scans the generated ELF objects to
> find this_pmd_name* symbol in symbol table.  Without fat-lto-objects gcc
> produces ELF only with extra symbols for internal use during linking and
> clang does not produce ELF at all (only LLVM IR bitcode).
> 
> Signed-off-by: Andrzej Ostruszka <aostruszka@marvell.com>
> ---
<snip>
> --- a/meson_options.txt
> +++ b/meson_options.txt
> @@ -6,6 +6,8 @@ option('drivers_install_subdir', type: 'string', value: 'dpdk/pmds-<VERSION>',
>  	description: 'Subdirectory of libdir where to install PMDs. Defaults to using a versioned subdirectory.')
>  option('enable_docs', type: 'boolean', value: false,
>  	description: 'build documentation')
> +option('enable_lto', type: 'boolean', value: false,
> +	description: 'Enable link time optimization')
>  option('enable_kmods', type: 'boolean', value: true,
>  	description: 'build kernel modules')
>  option('examples', type: 'string', value: '',

Should not need a new option here. There is already a built-in option
"b_lto" which we can reuse.

/Bruce
Andrzej Ostruszka Sept. 5, 2019, 9:43 a.m. UTC | #2
On 9/5/19 11:36 AM, Bruce Richardson wrote:
> Should not need a new option here. There is already a built-in option
> "b_lto" which we can reuse.

Thank you Bruce, I don't know much about meson so I missed that.
Will try to figure out how to use that.

Regards
Andrzej

PS. Apologies to all maintainers for possibly getting duplicates - I've
made a mistake in DPDK mailing list e-mail and have resent the patch
series to dev@dpdk.org separately.  Please reply to these so that
everything is visible to the community.
Bruce Richardson Sept. 5, 2019, 9:51 a.m. UTC | #3
On Thu, Sep 05, 2019 at 11:43:30AM +0200, Andrzej Ostruszka wrote:
> On 9/5/19 11:36 AM, Bruce Richardson wrote:
> > Should not need a new option here. There is already a built-in option
> > "b_lto" which we can reuse.
> 
> Thank you Bruce, I don't know much about meson so I missed that.
> Will try to figure out how to use that.
> 

No problem.
The options are documented here: https://mesonbuild.com/Builtin-options.html
and you can query them just the same as with the options added for the
project. Therefore, the only thing that really should change is that in the
meson.build file you check the built-in option and add the fat-lto-objects
flag. 

Incidentally, I think if the fat-lto-objects flag is not supported you may
want to error out if lto is enabled, as meson will add the lto flag itself
if the option is set.

Regards,
/Bruce

Patch
diff mbox series

diff --git a/.travis.yml b/.travis.yml
index 781f9f666..a9506b13a 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -31,6 +31,7 @@  env:
   - DEF_LIB="static" OPTS="-Denable_kmods=false"
   - DEF_LIB="shared" OPTS="-Denable_kmods=false"
   - DEF_LIB="shared" RUN_TESTS=1 BUILD_DOCS=1
+  - DEF_LIB="static" OPTS="-Denable_lto=true"
 
 matrix:
   include:
@@ -100,6 +101,12 @@  matrix:
       apt:
         packages:
           - *extra_packages
+  - env: DEF_LIB="static" OPTS="-Denable_lto=true" EXTRA_PACKAGES=1
+    compiler: gcc
+    addons:
+      apt:
+        packages:
+          - *extra_packages
 
 
 script: ./.ci/${TRAVIS_OS_NAME}-build.sh
diff --git a/config/common_base b/config/common_base
index 8ef75c203..73a55fdec 100644
--- a/config/common_base
+++ b/config/common_base
@@ -49,6 +49,11 @@  CONFIG_RTE_FORCE_INTRINSICS=n
 #
 CONFIG_RTE_ARCH_STRICT_ALIGN=n
 
+#
+# Enable link time optimization
+#
+CONFIG_RTE_ENABLE_LTO=n
+
 #
 # Compile to share library
 #
diff --git a/config/meson.build b/config/meson.build
index 2bafea530..b224d0cb8 100644
--- a/config/meson.build
+++ b/config/meson.build
@@ -196,3 +196,12 @@  add_project_arguments('-D_GNU_SOURCE', language: 'c')
 if is_freebsd
 	add_project_arguments('-D__BSD_VISIBLE', language: 'c')
 endif
+
+if get_option('enable_lto')
+	if cc.has_argument('-flto -ffat-lto-objects')
+		add_project_arguments('-flto -ffat-lto-objects', language: 'c')
+		add_project_link_arguments('-flto', language: 'c')
+	else
+		message('compiler does not support LTO')
+	endif
+endif
diff --git a/doc/guides/prog_guide/lto.rst b/doc/guides/prog_guide/lto.rst
new file mode 100644
index 000000000..effa0fcc3
--- /dev/null
+++ b/doc/guides/prog_guide/lto.rst
@@ -0,0 +1,36 @@ 
+Link Time Optimization
+======================
+
+The DPDK framework supports compilation with link time optimization
+turned on.  This depends obviously on the capabilities of the compiler
+to do "whole program" optimization at link time and is available only
+for compilers that support that feature (gcc, clang and icc).  To be
+more specific compiler have to support creation of ELF objects
+containing both normal code and internal representation
+(fat-lto-objects).  This is required since during build some code is
+generated by parsing produced ELF objects (pmdinfogen).
+
+The amount of performance gain that one can get from LTO depends on the
+compiler and the code that is being compiled.  However LTO is also
+useful for additional code analysis done by the compiler.  In particular
+due to interprocedural analysis compiler can produce additional warnings
+about variables that might be used uninitialized.  Some of these
+warnings might be "false positives" though and you might need to
+explicitly initialize variable in order to silence the compiler.
+
+Link time optimization can be enabled for whole DPDK framework by
+setting:
+
+.. code-block:: console
+    CONFIG_ENABLE_LTO=y
+
+in config file for the case of make based build and by:
+
+.. code-block:: console
+    meson build -Denable_lto=true
+    ninja -C build
+
+for the case of meson based build.
+
+Please note that turning LTO on causes considerable extension of
+compilation time.
diff --git a/doc/guides/rel_notes/release_19_11.rst b/doc/guides/rel_notes/release_19_11.rst
index 27cfbd9e3..639b7ed53 100644
--- a/doc/guides/rel_notes/release_19_11.rst
+++ b/doc/guides/rel_notes/release_19_11.rst
@@ -56,6 +56,14 @@  New Features
      Also, make sure to start the actual text at the margin.
      =========================================================
 
+**Added build support for Link Time Optimization.**
+
+ LTO is an optimization technique used by the compiler to perform whole
+ program analysis and optimization at link time.  In order to do that
+ compilers store their internal representation of the source code that
+ the linker uses at the final stage of compilation process.
+
+ See :doc:`../prog_guide/lto` for more information:
 
 Removed Items
 -------------
diff --git a/meson_options.txt b/meson_options.txt
index 448f3e63d..a315e0f82 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -6,6 +6,8 @@  option('drivers_install_subdir', type: 'string', value: 'dpdk/pmds-<VERSION>',
 	description: 'Subdirectory of libdir where to install PMDs. Defaults to using a versioned subdirectory.')
 option('enable_docs', type: 'boolean', value: false,
 	description: 'build documentation')
+option('enable_lto', type: 'boolean', value: false,
+	description: 'Enable link time optimization')
 option('enable_kmods', type: 'boolean', value: true,
 	description: 'build kernel modules')
 option('examples', type: 'string', value: '',
diff --git a/mk/toolchain/clang/rte.toolchain-compat.mk b/mk/toolchain/clang/rte.toolchain-compat.mk
index e6189b498..78f96c648 100644
--- a/mk/toolchain/clang/rte.toolchain-compat.mk
+++ b/mk/toolchain/clang/rte.toolchain-compat.mk
@@ -20,3 +20,7 @@  CLANG_MINOR_VERSION := $(shell echo $(CLANG_VERSION) | cut -f2 -d.)
 ifeq ($(shell test $(CLANG_MAJOR_VERSION)$(CLANG_MINOR_VERSION) -lt 35 && echo 1), 1)
 	CC_SUPPORTS_Z := false
 endif
+
+ifeq ($(shell test $(CLANG_MAJOR_VERSION)$(CLANG_MINOR_VERSION) -lt 60 && echo 1), 1)
+	CONFIG_RTE_ENABLE_LTO=n
+endif
diff --git a/mk/toolchain/clang/rte.vars.mk b/mk/toolchain/clang/rte.vars.mk
index 3c49dc568..3b1fa05f9 100644
--- a/mk/toolchain/clang/rte.vars.mk
+++ b/mk/toolchain/clang/rte.vars.mk
@@ -48,6 +48,14 @@  endif
 # process cpu flags
 include $(RTE_SDK)/mk/toolchain/$(RTE_TOOLCHAIN)/rte.toolchain-compat.mk
 
+ifeq ($(CONFIG_RTE_ENABLE_LTO),y)
+# 'fat-lto' is used since pmdinfogen needs to have 'this_pmd_nameX'
+# exported in symbol table and without this option only internal
+# representation is present.
+TOOLCHAIN_CFLAGS += -flto -ffat-lto-objects
+TOOLCHAIN_LDFLAGS += -flto
+endif
+
 # workaround clang bug with warning "missing field initializer" for "= {0}"
 WERROR_FLAGS += -Wno-missing-field-initializers
 
diff --git a/mk/toolchain/gcc/rte.toolchain-compat.mk b/mk/toolchain/gcc/rte.toolchain-compat.mk
index ea40a11c0..ad4fad83c 100644
--- a/mk/toolchain/gcc/rte.toolchain-compat.mk
+++ b/mk/toolchain/gcc/rte.toolchain-compat.mk
@@ -88,6 +88,10 @@  else
 		MACHINE_CFLAGS := $(filter-out -march% -mtune% -msse%,$(MACHINE_CFLAGS))
 	endif
 
+	ifeq ($(shell test $(GCC_VERSION) -lt 45 && echo 1), 1)
+		CONFIG_RTE_ENABLE_LTO=n
+	endif
+
 	# Disable thunderx PMD for gcc < 4.7
 	ifeq ($(shell test $(GCC_VERSION) -lt 47 && echo 1), 1)
 		CONFIG_RTE_LIBRTE_THUNDERX_NICVF_PMD=d
diff --git a/mk/toolchain/gcc/rte.vars.mk b/mk/toolchain/gcc/rte.vars.mk
index b852fcfd7..9fc704193 100644
--- a/mk/toolchain/gcc/rte.vars.mk
+++ b/mk/toolchain/gcc/rte.vars.mk
@@ -62,6 +62,18 @@  endif
 # process cpu flags
 include $(RTE_SDK)/mk/toolchain/$(RTE_TOOLCHAIN)/rte.toolchain-compat.mk
 
+ifeq ($(CONFIG_RTE_ENABLE_LTO),y)
+# 'fat-lto' is used since pmdinfogen needs to have 'this_pmd_nameX'
+# exported in symbol table and without this option only internal
+# representation is present.
+TOOLCHAIN_CFLAGS += -flto -ffat-lto-objects
+TOOLCHAIN_LDFLAGS += -flto
+# workaround for GCC bug 81440
+ifeq ($(shell test $(GCC_VERSION) -lt 80 && echo 1), 1)
+WERROR_FLAGS += -Wno-lto-type-mismatch
+endif
+endif
+
 # workaround GCC bug with warning "missing initializer" for "= {0}"
 ifeq ($(shell test $(GCC_VERSION) -lt 47 && echo 1), 1)
 WERROR_FLAGS += -Wno-missing-field-initializers
diff --git a/mk/toolchain/icc/rte.vars.mk b/mk/toolchain/icc/rte.vars.mk
index aa1422bf1..8aa87aa1e 100644
--- a/mk/toolchain/icc/rte.vars.mk
+++ b/mk/toolchain/icc/rte.vars.mk
@@ -54,5 +54,13 @@  endif
 # process cpu flags
 include $(RTE_SDK)/mk/toolchain/$(RTE_TOOLCHAIN)/rte.toolchain-compat.mk
 
+ifeq ($(CONFIG_RTE_ENABLE_LTO),y)
+# 'fat-lto' is used since pmdinfogen needs to have 'this_pmd_nameX'
+# exported in symbol table and without this option only internal
+# representation is present.
+TOOLCHAIN_CFLAGS += -flto -ffat-lto-objects
+TOOLCHAIN_LDFLAGS += -flto
+endif
+
 export CC AS AR LD OBJCOPY OBJDUMP STRIP READELF
 export TOOLCHAIN_CFLAGS TOOLCHAIN_LDFLAGS TOOLCHAIN_ASFLAGS