Re: [dpdk-dev] [PATCH v4 1/2] config/arm: select most suitable -march for kunpeng soc

[fengchengwen <fengchengwen@huawei.com>]

On 2021/5/14 7:12, Honnappa Nagarahalli wrote:
> <snip>
>>
>> On Thu, May 13, 2021 at 6:41 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-a', '-march=armv8.2-a'] 2. Define
>>> 'march_feature' tuple which defines support feature.
>>> e.g. 'march_feature' : ['crypto', 'sve'] 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 | 27 +++++++++++++++++++++++++--
>>>  1 file changed, 25 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/config/arm/meson.build b/config/arm/meson.build index
>>> 3f34ec9..8551a80 100644
>>> --- a/config/arm/meson.build
>>> +++ b/config/arm/meson.build
>>> @@ -149,7 +149,9 @@ implementer_hisilicon = {
>>>      ],
>>>      'part_number_config': {
>>>          '0xd01': {
>>> -            'machine_args': ['-march=armv8.2-a+crypto', '-mtune=tsv110'],
>>> +            'march_base' : ['-march=armv8-a', '-march=armv8.2-a'],
> If the compiler supports armv8.1-a, you need to choose armv8.1-a.
> 
>>
>> Another target has the same issue. Could you fix that all together as it is
>> generic problem in the existing infrastructure.
> I think this needs to be more generic solution. IMO, the requirement is as follows:
> 
> 1) We need to pick the most closest march_base supported by the compiler. For ex: If the SoC support v8.2 and the compiler supports v8.1, we need to pick v8.1
> 2) SoCs are allowed to support a base march version + hand picked features from the next 1 base marchs. i.e. armv8.x compliant implementation can include any features from armv8.(x + 1). Please refer to  Arm-ARM section A2 for more details. So, it is possible that the compiler supports a base march and a bunch of optional features from the next version. We need to test all the features allowed by the architecture and pick the ones that are supported in the compiler.
> 

I try to add 'march_base' : ['-march=armv8-a', '-march=armv8.5-a'] to cn10k, and then find it
can't work with ['RTE_ARM_FEATURE_ATOMICS', true] when using gcc7.2:
	[268/2250] Compiling C object lib/librte_stack.a.p/stack_rte_stack_lf.c.o
	FAILED: lib/librte_stack.a.p/stack_rte_stack_lf.c.o
	...
	{standard input}: Assembler messages:
	{standard input}:13: Error: selected processor does not support `caspl x0,x1,x2,x3,[x5]'
	[347/2250] Compiling C object lib/librte_hash.a.p/hash_rte_cuckoo_hash.c.o
	ninja: build stopped: subcommand failed.
	make: *** [cn10k] Error 1
It seem can't simplely add '-march=armv8-a' in 'march_base'.
And it require a lot of testing to get the right 'march_base' and 'march_feature' parameters.
So for v5, I just modify the kunpeng930's config which was well tested.

I think the 'march_base' and 'march_feature' could well solve the gcc's minor-version problem.
Note: the minor-version means a few version which are closes, not big gap, like gcc5.4 and gcc10.2

For that old gcc which could not support the 'march' that defined in 'machine_args' or 'march_base'
I think it better use the 'generic' profile else it will compile fail which showed above.

So how about add new tuple: fallback_generic? eg:
	'0xd02': {
            'march_base': ['-march=armv8.2-a'],
            'march_feature': ['crypto', 'sve'],
            'machine_args': [],
            'flags': [
                ['RTE_MACHINE', '"Kunpeng 930"'],
                ['RTE_ARM_FEATURE_ATOMICS', true],
                ['RTE_MAX_LCORE', 1280],
                ['RTE_MAX_NUMA_NODES', 16]
            ],
	    'fallback_generic': true
        }
PS: The premise is that the 'generic' profile is tested.


>>
>>
>>> +            'march_feature' : ['crypto'],
>>> +            'machine_args': ['-mtune=tsv110'],
>>>              'flags': [
>>>                  ['RTE_MACHINE', '"Kunpeng 920"'],
>>>                  ['RTE_ARM_FEATURE_ATOMICS', true], @@ -158,7 +160,9
>>> @@ implementer_hisilicon = {
>>>              ]
>>>          },
>>>          '0xd02': {
>>> -            'machine_args': ['-march=armv8.2-a+crypto+sve'],
>>> +            'march_base' : ['-march=armv8-a', '-march=armv8.2-a'],
>>> +            'march_feature' : ['crypto', 'sve'],
>>> +            'machine_args': [],
>>>              'flags': [
>>>                  ['RTE_MACHINE', '"Kunpeng 930"'],
>>>                  ['RTE_ARM_FEATURE_ATOMICS', true], @@ -449,8 +453,27
>>> @@ 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')
>>> +        foreach arch: part_number_config['march_base']
>>> +            if cc.has_argument(arch)
>>> +                machine_march = arch # Set the higher supported arch as
>> possible
>>> +            endif
>>> +        endforeach
>>> +    endif
>>> +    if part_number_config.has_key('march_feature')
>>> +        foreach feature: part_number_config['march_feature']
>>> +            tmp_machine_march = machine_march + '+' + feature
>>> +            if cc.has_argument(tmp_machine_march)
>>> +                machine_march = tmp_machine_march # Set the more supported
>> feature as possible
>>> +            endif
>>> +        endforeach
>>> +    endif
>>> +
>>>      # apply supported machine args
>>>      machine_args = [] # Clear previous machine args
>>> +    machine_args += machine_march
>>>      foreach flag: part_number_config['machine_args']
>>>          if cc.has_argument(flag)
>>>              machine_args += flag
>>> --
>>> 2.8.1
>>>