> -----Original Message-----
> From: Juraj Linkeš <juraj.lin...@pantheon.tech>
> Sent: Monday, January 22, 2024 9:57 PM
> To: Pavan Nikhilesh Bhagavatula <pbhagavat...@marvell.com>
> Cc: Jerin Jacob <jer...@marvell.com>; ruifeng.w...@arm.com;
> n...@arm.com; Bruce Richardson <bruce.richard...@intel.com>;
> dev@dpdk.org
> Subject: Re: [EXT] Re: [PATCH 1/2] config/arm: avoid mcpu and march
> conflicts
>
> On Mon, Jan 22, 2024 at 12:54 PM Pavan Nikhilesh Bhagavatula
> <pbhagavat...@marvell.com> wrote:
> >
> > > On Sun, Jan 21, 2024 at 10:37 AM <pbhagavat...@marvell.com> wrote:
> > > >
> > > > From: Pavan Nikhilesh <pbhagavat...@marvell.com>
> > > >
> > > > The compiler options march and mtune are a subset
> > > > of mcpu and will lead to conflicts if improper march
> > > > is chosen for a given mcpu.
> > > > To avoid conflicts, force part number march when
> > > > mcpu is available and is supported by the compiler.
> > > >
> > > > Example:
> > > > march = armv9-a
> > > > mcpu = neoverse-n2
> > > >
> > > > mcpu supported, march supported
> > > > machine_args = ['-mcpu=neoverse-n2', '-march=armv9-a']
> > > >
> > > > mcpu supported, march not supported
> > > > machine_args = ['-mcpu=neoverse-n2']
> > > >
> > > > mcpu not supported, march supported
> > > > machine_args = ['-march=armv9-a']
> > > >
> > > > mcpu not supported, march not supported
> > > > machine_args = ['-march=armv8.6-a']
> > > >
> > > > Signed-off-by: Pavan Nikhilesh <pbhagavat...@marvell.com>
> > > > ---
> > > > config/arm/meson.build | 109 +++++++++++++++++++++++++---------
> -----
> > > --
> > > > 1 file changed, 67 insertions(+), 42 deletions(-)
> > > >
> > > > diff --git a/config/arm/meson.build b/config/arm/meson.build
> > > > index 36f21d2259..8c8cfccca0 100644
> > > > --- a/config/arm/meson.build
> > > > +++ b/config/arm/meson.build
> > > <snip>
> > > > @@ -127,21 +128,22 @@ implementer_cavium = {
> > > > ],
> > > > 'part_number_config': {
> > > > '0xa1': {
> > > > - 'compiler_options': ['-mcpu=thunderxt88'],
> > > > + 'mcpu': 'thunderxt88',
> > > > 'flags': flags_part_number_thunderx
> > > > },
> > > > '0xa2': {
> > > > - 'compiler_options': ['-mcpu=thunderxt81'],
> > > > + 'mcpu': 'thunderxt81',
> > > > 'flags': flags_part_number_thunderx
> > > > },
> > > > '0xa3': {
> > > > - 'compiler_options': ['-march=armv8-a+crc', '-
> mcpu=thunderxt83'],
> > > > + 'mcpu': 'thunderxt83',
> > > > + 'compiler_options': ['-march=armv8-a+crc'],
> > >
> > > Let's unify this with the rest and specify 'march': 'armv8-a+crc'
> > > instead of having it under compiler_options.
> >
> > Ack.
> >
> > >
> > > > 'flags': flags_part_number_thunderx
> > > > },
> > > > '0xaf': {
> > > > 'march': 'armv8.1-a',
> > > > 'march_features': ['crc', 'crypto'],
> > > > - 'compiler_options': ['-mcpu=thunderx2t99'],
> > > > + 'mcpu': 'thunderx2t99',
> > > > 'flags': [
> > > > ['RTE_MACHINE', '"thunderx2"'],
> > > > ['RTE_ARM_FEATURE_ATOMICS', true],
> > > > @@ -153,7 +155,7 @@ implementer_cavium = {
> > > > '0xb2': {
> > > > 'march': 'armv8.2-a',
> > > > 'march_features': ['crc', 'crypto', 'lse'],
> > > > - 'compiler_options': ['-mcpu=octeontx2'],
> > > > + 'mcpu': 'octeontx2',
> > > > 'flags': [
> > > > ['RTE_MACHINE', '"cn9k"'],
> > > > ['RTE_ARM_FEATURE_ATOMICS', true],
> > > > @@ -176,7 +178,7 @@ implementer_ampere = {
> > > > '0x0': {
> > > > 'march': 'armv8-a',
> > > > 'march_features': ['crc', 'crypto'],
> > > > - 'compiler_options': ['-mtune=emag'],
> > > > + 'mcpu': 'emag',
> > >
> > > We're changing mtune to mcpu, is this equivalent?
> > >
> >
> > Both march and mtune are a subset of mcpu.
> >
>
> Sure, but we replaced '-mtune=emag' with '-mcpu=emag'. Are these two
> builds going to be different or the same?
>
Yeah, I believe both are same.
> > > > 'flags': [
> > > > ['RTE_MACHINE', '"eMAG"'],
> > > > ['RTE_MAX_LCORE', 32],
> > > > @@ -186,7 +188,7 @@ implementer_ampere = {
> > > > '0xac3': {
> > > > 'march': 'armv8.6-a',
> > > > 'march_features': ['crc', 'crypto'],
> > > > - 'compiler_options': ['-mcpu=ampere1'],
> > > > + 'mcpu': 'ampere1',
> > > > 'flags': [
> > > > ['RTE_MACHINE', '"AmpereOne"'],
> > > > ['RTE_MAX_LCORE', 320],
> > > > @@ -206,7 +208,7 @@ implementer_hisilicon = {
> > > > '0xd01': {
> > > > 'march': 'armv8.2-a',
> > > > 'march_features': ['crypto'],
> > > > - 'compiler_options': ['-mtune=tsv110'],
> > > > + 'mcpu': 'tsv110',
> > > > 'flags': [
> > > > ['RTE_MACHINE', '"Kunpeng 920"'],
> > > > ['RTE_ARM_FEATURE_ATOMICS', true],
> > > > @@ -695,11 +697,23 @@ if update_flags
> > > >
> > > > machine_args = [] # Clear previous machine args
> > > >
> > > > + candidate_mcpu = ''
> > > > + support_mcpu = false
> > > > + if part_number_config.has_key('mcpu')
> > > > + mcpu = part_number_config['mcpu']
> > > > + if (cc.has_argument('-mcpu=' + mcpu))
> > > > + candidate_mcpu = mcpu
> > > > + support_mcpu = true
> > > > + endif
> > > > + endif
> > > > +
> > > > # probe supported archs and their features
> > > > candidate_march = ''
> > > > if part_number_config.has_key('march')
> > > > - if part_number_config.get('force_march', false)
> > > > - candidate_march = part_number_config['march']
> > > > + if part_number_config.get('force_march', false) or support_mcpu
> > >
> > > Instead of using the extra "support_mcpu" variable, we could do the
> > > same check as with candidate march (if candidate_mcpu != '', which we
> > > actually do below in the last lines of the patch).
> > >
> >
> > Ack.
> >
> > > If I understand the logic correctly, we don't want to do the march
> > > fallback if mcpu is specified - either the march works with the given
> > > mcpu or we do without it (because we don't actually need it with
> > > mcpu). Is that correct?
> > >
> >
> > Yes, but still exact march defined in part_number_config should be present
> for setting extra_march_features.
> > specially for expressing crypto support.
> >
>
> Ok, thanks.
>
> > > > + if cc.has_argument('-march=' +
> > > > part_number_config['march'])
> > >
> > > Now that we've added mcpu into the mix, is this still the right
> > > condition? Can the below happen?
> > >
> > > This check finds that machine_args = ['-march=armv9-a'] is supported.
> > >
> > > But taken together with mcpu (machine_args = ['-mcpu=neoverse-n2',
> > > '-march=armv9-a']), it is not supported? In this case we'll end up
> > > with invalid configuration.
> >
> > This is the only correct option and evolves into -march=armv9-
> a+sve2+crypto for cn10k
> > whereas other neoverse-n2 might only have -march=armv9-a+sve2.
> >
>
> Maybe I should rephrase my question a bit:
>
> The correct options are ['-mcpu=neoverse-n2', '-march=armv9-a']. Is it
> possible that the compiler will say:
>
> ['-mcpu=neoverse-n2', '-march=armv9-a'] is supported
> ['-mcpu=neoverse-n2'] is supported
> ['-march=armv9-a'] is not supported
>
Yes, this is possible.
> So basically the question is are we risking that the compiler will say
> it supports both options only when both are passed while also saying
> it doesn't support one or both of them when checked alone. We've seen
> this behavior with newer compilers in aarch32 builds
> (-march=armv8-a+simd -mfpu=auto are supported when both are passed,
> but -march=armv8-a is not supported alone), so I wanted to be sure.
>
> > Example:
> >
> > Good:
> > #aarch64-linux-gnu-gcc -march=armv9-a+sve2+crypto -mcpu=neoverse-n2
> shrn.c
> > #aarch64-linux-gnu-gcc -march=armv9-a+sve2 -mcpu=neoverse-n2 shrn.c
> > #aarch64-linux-gnu-gcc -march=armv9-a -mcpu=neoverse-n2 shrn.c
> >
> > Bad:
> > #aarch64-linux-gnu-gcc -mcpu=neoverse-n2 -march=armv8-a shrn.c
> > cc1: warning: switch '-mcpu=neoverse-n2' conflicts with '-march=armv8-a'
> switch
> > #aarch64-linux-gnu-gcc -mcpu=neoverse-n2 -march=armv8.1-a shrn.c
> > cc1: warning: switch '-mcpu=neoverse-n2' conflicts with '-march=armv8.1-a'
> switch
> > #aarch64-linux-gnu-gcc -mcpu=neoverse-n2 -march=armv8.2-a shrn.c
> > cc1: warning: switch '-mcpu=neoverse-n2' conflicts with '-march=armv8.2-a'
> switch
> > #aarch64-linux-gnu-gcc -mcpu=neoverse-n2 -march=armv8.3-a shrn.c
> > cc1: warning: switch '-mcpu=neoverse-n2' conflicts with '-march=armv8.3-a'
> switch
> > #aarch64-linux-gnu-gcc -mcpu=neoverse-n2 -march=armv8.4-a shrn.c
> > cc1: warning: switch '-mcpu=neoverse-n2' conflicts with '-march=armv8.4-a'
> switch
> > #aarch64-linux-gnu-gcc -mcpu=neoverse-n2 -march=armv8.5-a shrn.c
> > cc1: warning: switch '-mcpu=neoverse-n2' conflicts with '-march=armv8.5-a'
> switch
> > #aarch64-linux-gnu-gcc -mcpu=neoverse-n2 -march=armv8.6-a shrn.c
> > cc1: warning: switch '-mcpu=neoverse-n2' conflicts with '-march=armv8.6-a'
> switch
> > #aarch64-linux-gnu-gcc -mcpu=neoverse-n2 -march=armv8.7-a shrn.c
> > cc1: warning: switch '-mcpu=neoverse-n2' conflicts with '-march=armv8.7-a'
> switch
> >
> > >
> > > > + candidate_march = part_number_config['march']
> > > > + endif
> > > > else
> > > > supported_marchs = ['armv8.6-a', 'armv8.5-a', 'armv8.4-a',
> 'armv8.3-
> > > a',
> > > > 'armv8.2-a', 'armv8.1-a', 'armv8-a']
