Re: [dpdk-dev] [RFC PATCH v2] build: add platform meson option

[Bruce Richardson <bruce.richardson@intel.com>]

On Tue, Jan 05, 2021 at 02:17:44PM -0800, David Christensen wrote:
> > > The current meson option 'machine' should only specify the ISA, which is not
> > > sufficient for Arm, where setting ISA implies other setting as well.
> > > Add a new meson option, 'platform', which differentiates the type of the build
> > > (native/generic) and sets 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 backward
> > > compatibility.
> > > These two new variables, taken together, achieve what 'machine' was setting
> > > per architecture - setting the ISA in x86 build and setting native/default 'build
> > > type' in aarch64 build - is now properly being set for all architectures in a
> > > uniform manner.
> > > 
> > > Signed-off-by: Juraj Linkeš <juraj.linkes@pantheon.tech>
> > > ---
> > >   config/arm/meson.build        |  4 +--
> > >   config/meson.build            | 47 +++++++++++++++++++++++++----------
> > >   devtools/test-meson-builds.sh |  9 ++++---
> > >   meson_options.txt             |  8 ++++--
> > >   4 files changed, 47 insertions(+), 21 deletions(-)
> > > 
> > > diff --git a/config/arm/meson.build b/config/arm/meson.build index
> > > 42b4e43c7..6b09a74a7 100644
> > > --- a/config/arm/meson.build
> > > +++ b/config/arm/meson.build
> > > @@ -3,10 +3,10 @@
> > >   # Copyright(c) 2017 Cavium, Inc
> > > 
> > >   # for checking defines we need to use the correct compiler flags -march_opt = '-
> > > march=@0@'.format(machine)
> > > +march_opt = '-march=@0@'.format(cpu_instruction_set)
> > > 
> > >   arm_force_native_march = false
> > > -arm_force_default_march = (machine == 'default')
> > > +arm_force_default_march = (platform == 'generic')
> > > 
> > >   flags_common_default = [
> > >   	# Accelarate rte_memcpy. Be sure to run unit test
> > > (memcpy_perf_autotest) diff --git a/config/meson.build b/config/meson.build
> > > index a3154e29c..647116513 100644
> > > --- a/config/meson.build
> > > +++ b/config/meson.build
> > > @@ -63,42 +63,63 @@ if not is_windows
> > >   			pmd_subdir_opt)
> > >   endif
> > > 
> > > -# set the machine type and cflags for it
> > > +platform = get_option('platform')
> > > +
> > > +# set the cpu_instruction_set type 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 = 'default'
> > > +	endif
> > >   endif
> > > 
> > > -# machine type 'default' is special, it defaults to the per arch agreed common
> > > +if cpu_instruction_set == 'default'
> > > +# cpu_instruction_set type 'default' is special, it defaults to the per
> > > +arch agreed common
> > >   # minimal baseline needed for DPDK.
> > >   # 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'
> > >   	if host_machine.cpu_family().startswith('x86')
> > >   		# matches the old pre-meson build systems default
> > > -		machine = 'corei7'
> > > +		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 defaults in config/arm/meson.build
> > > -		machine = 'default'
> > > +		cpu_instruction_set = 'default'
> > >   	elif host_machine.cpu_family().startswith('ppc')
> > > -		machine = 'power8'
> > > +		cpu_instruction_set = 'power8'
> > >   	endif
> > >   endif
> 
> This change forces the build on a P9 system to use the P8 instruction set.
> Prior to this change the "native" machine type was used which resulted in P9
> instructions when built on a P9 system.  How do I force the build to use the
> power9 instruction set in this case?
> 
> Dave

From looking at the patch, setting the "platform" to "native", or the
instruction_set to "native" should do this.
While I consider generic builds a good thing, I wonder if there is an
expectation that "native" is always the default build type for DPDK builds?

/Bruce