Re: [dpdk-dev] [PATCH v6 1/2] config/arm: select most suitable -march for kunpeng soc

[Jerin Jacob <jerinjacobk@gmail.com>]

On Wed, May 19, 2021 at 6:58 PM Chengwen Feng <fengchengwen@huawei.com> wrote:
>
> Currently, the soc_kunpeng930 declares '-march=armv8.2-a+crypto+sve',
> but some compiler doesn't recognize the march because it doesn't
> support sve.
>
> To solve this bug we use the following scheme:
> 1. Define 'march_base' tuple which defines support march, it should
> arrange from lower to higher.
> e.g. 'march_base': ['-march=armv8.1-a', '-march=armv8.2-a']
> 2. Define 'march_feature' tuple which defines support feature.
> e.g. 'march_feature': ['crypto', 'sve']
> Note: If user defined 'march_feature', it also needs to define a valid
> 'march_base' because 'march_feature' depends on 'march_base' when
> checking validity.
> 3. Select the most suitable march+feature combination based on
> 'march_base' and 'march_feature' tuples.
> 4. Use the selected march+feature combination as the default
> machine_args.
>
> Fixes: 7cf32a22b240 ("config/arm: add Hisilicon kunpeng")
>
> Signed-off-by: Chengwen Feng <fengchengwen@huawei.com>
> ---
>  config/arm/meson.build | 31 +++++++++++++++++++++++++++++--
>  1 file changed, 29 insertions(+), 2 deletions(-)
>
> diff --git a/config/arm/meson.build b/config/arm/meson.build
> index 3f34ec9..044812f 100644
> --- a/config/arm/meson.build
> +++ b/config/arm/meson.build
> @@ -158,7 +158,9 @@ implementer_hisilicon = {
>              ]
>          },
>          '0xd02': {
> -            'machine_args': ['-march=armv8.2-a+crypto+sve'],
> +            'march_base': ['-march=armv8.2-a'],
> +            'march_feature': ['crypto', 'sve'],
> +            'machine_args': [],

IMO, This patch must split into two as this problem is not specific to kunpeng
patch 1: config/arm: infrastructure to add most suitable -march or
so(This will have only infra)
patch 2: config/arm: update the targets to support most suitable
-march or so(This one will one will have changes for all targets
including kunpeng)




>              'flags': [
>                  ['RTE_MACHINE', '"Kunpeng 930"'],
>                  ['RTE_ARM_FEATURE_ATOMICS', true],
> @@ -449,8 +451,33 @@ else
>      # add/overwrite flags in the proper order
>      dpdk_flags = flags_common + implementer_config['flags'] + part_number_config.get('flags', []) + soc_flags
>
> +    # select the most suitable march+feature combination
> +    machine_march = []
> +    if part_number_config.has_key('march_base')
> +        tmp_machine_march = ''
> +        march_valid = false
> +        foreach march: part_number_config['march_base']
> +            if cc.has_argument(march)
> +                tmp_machine_march = march # Set the higher supported march as possible
> +                march_valid = true
> +            endif
> +        endforeach
> +        # select feature only when march valid
> +        if march_valid and part_number_config.has_key('march_feature')

I think, in order to make more generic, IMO, it should be
1) List all the march and features options(crypto, sve)
2) Probe the compiler to find the supported march, features
3) In each target,
- define the minimum march and features
- define the the best need march and features
4) If the compiler support the best config, pick that
else
5) If the compiler supports the minimum config, pick that
else
6) Don't build and throw the error.


> +            foreach feature: part_number_config['march_feature']
> +                tmp_feature = tmp_machine_march + '+' + feature
> +                if cc.has_argument(tmp_feature)
> +                    tmp_machine_march = tmp_feature # Set the more supported feature as possible
> +                endif
> +            endforeach
> +        endif
> +        if march_valid
> +            machine_march = [tmp_machine_march]
> +        endif
> +    endif
> +
>      # apply supported machine args
> -    machine_args = [] # Clear previous machine args
> +    machine_args = machine_march # Init with machine march which set above
>      foreach flag: part_number_config['machine_args']
>          if cc.has_argument(flag)
>              machine_args += flag
> --
> 2.8.1
>