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

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

> -----Original Message-----
> From: David Christensen <drc@linux.vnet.ibm.com>
> Sent: Monday, February 22, 2021 10:25 PM
> To: Juraj Linkeš <juraj.linkes@pantheon.tech>; Bruce Richardson
> <bruce.richardson@intel.com>
> Cc: thomas@monjalon.net; Honnappa.Nagarahalli@arm.com; dev@dpdk.org
> Subject: Re: [RFC PATCH v2] build: add platform meson option
> 
> 
> 
> On 2/19/21 1:11 AM, Juraj Linkeš wrote:
> >
> >
> >> -----Original Message-----
> >> From: Bruce Richardson <bruce.richardson@intel.com>
> >> Sent: Wednesday, January 6, 2021 3:43 PM
> >> To: David Christensen <drc@linux.vnet.ibm.com>
> >> Cc: Juraj Linkeš <juraj.linkes@pantheon.tech>; thomas@monjalon.net;
> >> Honnappa.Nagarahalli@arm.com; dev@dpdk.org
> >> Subject: Re: [RFC PATCH v2] build: add platform meson option
> >>
> >> 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
> >
> > I left this patch alone so that people could chime in, but noone did, so let's try
> to find some agreeable solution.
> >
> > My current thoughts are as such:
> > The platform parameter specifies a set of DPDK options that will be used. This
> is what arm uses for its builds, x86 and ppc don't use this.
> > The cpu_instruction_set sets just one configuration among the "platform"
> configuration set.
> > We want the build to work on most machines of the machine architecture.
> That implies platform=generic (as in use config options that will work on
> everything of that architecture) and cpu_instruction_set=generic (as in use ISA
> that will work on all cpus of the build machine architecture).
> > Setting cpu_instruction_set=generic changes the build without cmdline options
> for ppc. Thus, the expectation may be that cpu_instruction_set should be native
> by default.
> >
> > For arm, cpu_instruction_set is ignored (and thus the value doen't matter),
> since we can't use that without other config options (e.g. DPDK config for an
> SoC (such as RTE_ARM_FEATURE_ATOMICS) used with an invalid
> cpu_instuction_set). That means the only relevant parameter for Arm is platform
> and if we want to have a build usable on most machines of the build type, we
> have to use platform=generic.
> >
> > For x86 and ppc, there's no difference between native and generic platform (as
> it's a new argument, the purpose of which is to differentiate DPDK config across
> platforms, which doesn't exist for x86 and ppc - DPDK config is the same (correct
> me if I'm wrong)).
> >
> > So it basically boils down to what should be the default value of
> cpu_instruction_set when platform=generic (for platform=native, it's obviously
> native):
> > 1. cpu_instruction_set=native, this would preserve the current behavior, but
> we won't use the 'auto' default. I think we can fall back to this if we don't agree
> on anything better.
> > 2. cpu_instruction_set=auto, the same as cpu_instruction_set=generic,
> > 3. cpu_instruction_set=generic, this changes behavior for ppc builds, but we
> may be able to remedy this:
> > Similarly to arm (arm is using platform for this, but the idea is the same), if
> cpu_instruction_set is generic, we can do some discovery for pcc and set the ISA
> accordingly (either power8 or power9). If I understand it correctly, power8 is a
> different architecture from power9 (I could be wrong on this), so this is
> desirable. There's some logic in config/ppc/meson.build, but it doesn't seem
> sufficient as a discovery mechanism between power8/power9.
> 
> POWER8 code (Power ISA v2.07) runs on POWER9 CPUs (Power ISA v3.0), so
> setting cpu_instruction_set to GENERIC is a reasonable option. POWER10 CPUs
> (Power ISA v3.1) are around the corner so I want to make sure developers can
> tune the application for the platform as easily as possible.  I'm fine with
> supporting GENERIC, just need clear instructions on how to build for a particular
> ISA.
> 

That's good to hear. Setting cpu_instruction_set will set the ISA.

We'll need to document the behavior properly, but I'm not sure where - Bruce? Seems like meson_options.txt doesn't have enough room for that.

The default bahavior is the ISA will be set according to the platform parameter. If cpu_instruction_set is specified, that value will be used.

> Dave