[dpdk-dev] [PATCH v5] build: use platform option for generic and native

["Juraj Linkeš" <juraj.linkes@pantheon.tech>]

The current meson option 'machine' should only specify the ISA, which is
not sufficient for Arm, where setting ISA implies other setting as well.
Use the existing 'platform' meson option to differentiate the type of
the build (native/generic) and set machine accordingly, unless the user
chooses to override it.
The 'machine' option also doesn't describe very well what it sets, so
introduce a new option 'cpu_instruction_set', but keep 'machine' for
backwards compatibility.
'machine' was setting the ISA in x86 builds and setting native/default
'build type' in aarch64 builds. These two new variables, taken
together, are now properly setting both for all architectures in a
uniform manner.

Signed-off-by: Juraj Linkeš <juraj.linkes@pantheon.tech>
---
 config/arm/meson.build              |  6 ++--
 config/meson.build                  | 53 ++++++++++++++++++++---------
 devtools/test-meson-builds.sh       |  9 ++---
 doc/guides/linux_gsg/build_dpdk.rst | 28 ++++++++++++++-
 meson_options.txt                   | 10 +++---
 5 files changed, 78 insertions(+), 28 deletions(-)

diff --git a/config/arm/meson.build b/config/arm/meson.build
index 86cdb9b53b..59c788f1fa 100644
--- a/config/arm/meson.build
+++ b/config/arm/meson.build
@@ -347,7 +347,7 @@ else
 	soc = get_option('platform')
 	soc_config = {}
 	if not meson.is_cross_build()
-		if machine == 'generic'
+		if platform == 'generic'
 			# generic build
 			if soc != ''
 				error('Building for a particular platform is ' +
@@ -402,7 +402,7 @@ else
 	else
 		error('Unsupported Arm implementer: @0@. '.format(implementer_id) +
 		      'Please add support for it or use the generic ' +
-		      '(-Dmachine=generic) build.')
+		      '(-Dplatform=generic) build.')
 	endif
 
 	message('Arm implementer: ' + implementer_config['description'])
@@ -417,7 +417,7 @@ else
 		error('Unsupported part number @0@ of implementer @1@. '
 		      .format(part_number, implementer_id) +
 		      'Please add support for it or use the generic ' +
-		      '(-Dmachine=generic) build.')
+		      '(-Dplatform=generic) build.')
 	endif
 
 	# add/overwrite flags in the proper order
diff --git a/config/meson.build b/config/meson.build
index 6e6ef8c0e1..1b6dcab8f5 100644
--- a/config/meson.build
+++ b/config/meson.build
@@ -67,43 +67,64 @@ endif
 disable_drivers = ''
 enable_drivers = ''
 
-# set the machine type and cflags for it
+platform = get_option('platform')
+
+# set the cpu_instruction_set and cflags for it
 if meson.is_cross_build()
-	machine = host_machine.cpu()
+	cpu_instruction_set = host_machine.cpu()
 else
-	machine = get_option('machine')
+	cpu_instruction_set = get_option('cpu_instruction_set')
+	if get_option('machine') != 'auto'
+		warning('The "machine" option is deprecated. ' +
+		        'Please use "cpu_instruction_set" instead.')
+		if cpu_instruction_set != 'auto'
+			error('Setting both "machine" and ' +
+			      '"cpu_instruction_set" is unsupported.')
+		endif
+		cpu_instruction_set = get_option('machine')
+	endif
+endif
+
+if platform == 'native'
+	if cpu_instruction_set == 'auto'
+		cpu_instruction_set = 'native'
+	endif
+elif platform == 'generic'
+	if cpu_instruction_set == 'auto'
+		cpu_instruction_set = 'generic'
+	endif
 endif
 
-# machine type 'generic' is special, it selects the per arch agreed common
-# minimal baseline needed for DPDK. Machine type 'default' is also supported
-# with the same meaning for backwards compatibility.
+# cpu_instruction_set 'generic' is special, it selects the per arch agreed
+# common minimal baseline needed for DPDK. cpu_instruction_set 'default' is
+# also supported with the same meaning for backwards compatibility.
 # That might not be the most optimized, but the most portable version while
 # still being able to support the CPU features required for DPDK.
 # This can be bumped up by the DPDK project, but it can never be an
 # invariant like 'native'
-if machine == 'default' or machine == 'generic'
+if cpu_instruction_set == 'generic' or cpu_instruction_set == 'default'
 	if host_machine.cpu_family().startswith('x86')
-		# matches the old pre-meson build systems generic machine
-		machine = 'corei7'
+		# matches the old pre-meson build systems generic cpu_instruction_set
+		cpu_instruction_set = 'corei7'
 	elif host_machine.cpu_family().startswith('arm')
-		machine = 'armv7-a'
+		cpu_instruction_set = 'armv7-a'
 	elif host_machine.cpu_family().startswith('aarch')
 		# arm64 manages generic config in config/arm/meson.build
-		machine = 'generic'
+		cpu_instruction_set = 'generic'
 	elif host_machine.cpu_family().startswith('ppc')
-		machine = 'power8'
+		cpu_instruction_set = 'power8'
 	endif
 endif
 
-dpdk_conf.set('RTE_MACHINE', machine)
+dpdk_conf.set('RTE_MACHINE', cpu_instruction_set)
 machine_args = []
 
 # ppc64 does not support -march= at all, use -mcpu and -mtune for that
 if host_machine.cpu_family().startswith('ppc')
-	machine_args += '-mcpu=' + machine
-	machine_args += '-mtune=' + machine
+	machine_args += '-mcpu=' + cpu_instruction_set
+	machine_args += '-mtune=' + cpu_instruction_set
 else
-	machine_args += '-march=' + machine
+	machine_args += '-march=' + cpu_instruction_set
 endif
 
 toolchain = cc.get_id()
diff --git a/devtools/test-meson-builds.sh b/devtools/test-meson-builds.sh
index daf817ac3e..7edbd6c717 100755
--- a/devtools/test-meson-builds.sh
+++ b/devtools/test-meson-builds.sh
@@ -223,12 +223,13 @@ done
 # test compilation with minimal x86 instruction set
 # Set the install path for libraries to "lib" explicitly to prevent problems
 # with pkg-config prefixes if installed in "lib/x86_64-linux-gnu" later.
-generic_machine='nehalem'
-if ! check_cc_flags "-march=$generic_machine" ; then
-	generic_machine='corei7'
+generic_isa='nehalem'
+if ! check_cc_flags "-march=$generic_isa" ; then
+	generic_isa='corei7'
 fi
 build build-x86-generic cc skipABI -Dcheck_includes=true \
-	-Dlibdir=lib -Dmachine=$generic_machine $use_shared
+	-Dlibdir=lib -Dcpu_instruction_set=$generic_isa \
+	$use_shared
 
 # 32-bit with default compiler
 if check_cc_flags '-m32' ; then
diff --git a/doc/guides/linux_gsg/build_dpdk.rst b/doc/guides/linux_gsg/build_dpdk.rst
index f78eef2517..787b2c2d1f 100644
--- a/doc/guides/linux_gsg/build_dpdk.rst
+++ b/doc/guides/linux_gsg/build_dpdk.rst
@@ -89,7 +89,33 @@ to a regular "debug" build, you can either:
 * run ``meson configure -Dbuildtype=debug`` inside the build folder after the initial meson run.
 
 Other options are specific to the DPDK project but can be adjusted similarly.
-To set the "max_lcores" value to 256, for example, you can either:
+The "platform" option specifies a set a configuration parameters that will be
+used. The valid values are:
+
+* ``-Dplatform=native`` will tailor the configuration to the build machine.
+
+* ``-Dplatform=generic`` will use configuration that works on all machines
+of the same architecture as the build machine.
+
+* ``-Dplatform=<Arm_SoC>`` will use configuration optimized for a particular
+Arm SoC. Consult the "socs" dictionary in config/arm/meson.build to see which
+SoC are supported.
+
+An important configuration parameter that "platform" sets is the instruction
+set to use in x86 and ppc builds:
+
+* ``-Dplatform=native`` sets "cpu_instruction_set" to "native", which
+configures -march, -mcpu, -mtune to "native".
+
+* ``-Dplatform=generic`` sets "cpu_instruction_set" to "generic", which
+configures -march, -mcpu, -mtune to a common minimal baseline needed for DPDK.
+
+"cpu_instruction_set" is not used in Arm builds, as setting the instruction set
+without other parameters leads to inferior builds. The way to tailor Arm builds
+is to build for an SoC or a native build using the "platform" option.
+
+The values determined by the "platform" parameter may be overwritten. For
+example, to set the "max_lcores" value to 256, you can either:
 
 * pass ``-Dmax_lcores=256`` to meson when configuring the build folder initially
 
diff --git a/meson_options.txt b/meson_options.txt
index b78f3bd9d5..07db5146db 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -2,6 +2,8 @@
 
 option('check_includes', type: 'boolean', value: false,
 	description: 'build "chkincs" to verify each header file can compile alone')
+option('cpu_instruction_set', type: 'string', value: 'auto',
+	description: 'Set the target machine ISA (instruction set architecture). Will be set according to the platform option by default.')
 option('developer_mode', type: 'feature',
 	description: 'turn on additional build checks relevant for DPDK developers')
 option('disable_drivers', type: 'string', value: '',
@@ -26,16 +28,16 @@ option('include_subdir_arch', type: 'string', value: '',
 	description: 'subdirectory where to install arch-dependent headers')
 option('kernel_dir', type: 'string', value: '',
 	description: 'Path to the kernel for building kernel modules. Headers must be in $kernel_dir or $kernel_dir/build. Modules will be installed in /lib/modules.')
-option('machine', type: 'string', value: 'native',
-	description: 'set the target machine type or "generic", a build usable on all machines of the build machine architecture or "native", which lets the compiler pick the architecture of the build machine.')
+option('machine', type: 'string', value: 'auto',
+	description: 'Alias of cpu_instruction_set.')
 option('max_ethports', type: 'integer', value: 32,
 	description: 'maximum number of Ethernet devices')
 option('max_lcores', type: 'integer', value: 128,
 	description: 'maximum number of cores/threads supported by EAL')
 option('max_numa_nodes', type: 'integer', value: 32,
 	description: 'maximum number of NUMA nodes supported by EAL')
-option('platform', type: 'string', value: '',
-	description: 'use configuration for a particular platform (such as a SoC).')
+option('platform', type: 'string', value: 'generic',
+	description: 'Platform to build, either "native", "generic" or an Arm SoC. Please refer to the Linux build guide for more information.')
 option('enable_trace_fp', type: 'boolean', value: false,
 	description: 'enable fast path trace points.')
 option('tests', type: 'boolean', value: true,
-- 
2.20.1