Re: [dpdk-dev] [PATCH v6 2/2] net/hns3: refactor SVE code compile method

[fengchengwen <fengchengwen@huawei.com>]

On 2021/5/24 13:38, Ruifeng Wang wrote:
>> -----Original Message-----
>> From: fengchengwen <fengchengwen@huawei.com>
>> Sent: Friday, May 21, 2021 2:53 PM
>> To: Ruifeng Wang <Ruifeng.Wang@arm.com>; thomas@monjalon.net;
>> ferruh.yigit@intel.com
>> Cc: dev@dpdk.org; jerinj@marvell.com; viktorin@rehivetech.com;
>> bruce.richardson@intel.com; Honnappa Nagarahalli
>> <Honnappa.Nagarahalli@arm.com>; jerinjacobk@gmail.com;
>> juraj.linkes@pantheon.tech; nd <nd@arm.com>
>> Subject: Re: [PATCH v6 2/2] net/hns3: refactor SVE code compile method
>>
>>
>>
>> On 2021/5/21 13:21, Ruifeng Wang wrote:
>>>> -----Original Message-----
>>>> From: fengchengwen <fengchengwen@huawei.com>
>>>> Sent: Thursday, May 20, 2021 6:55 PM
>>>> To: Ruifeng Wang <Ruifeng.Wang@arm.com>; thomas@monjalon.net;
>>>> ferruh.yigit@intel.com
>>>> Cc: dev@dpdk.org; jerinj@marvell.com; viktorin@rehivetech.com;
>>>> bruce.richardson@intel.com; Honnappa Nagarahalli
>>>> <Honnappa.Nagarahalli@arm.com>; jerinjacobk@gmail.com;
>>>> juraj.linkes@pantheon.tech; nd <nd@arm.com>
>>>> Subject: Re: [PATCH v6 2/2] net/hns3: refactor SVE code compile
>>>> method
>>>>
>>>>
>>>>
>>>> On 2021/5/20 16:24, Ruifeng Wang wrote:
>>>>>> -----Original Message-----
>>>>>> From: Chengwen Feng <fengchengwen@huawei.com>
>>>>>> Sent: Wednesday, May 19, 2021 9:26 PM
>>>>>> To: thomas@monjalon.net; ferruh.yigit@intel.com
>>>>>> Cc: dev@dpdk.org; jerinj@marvell.com; Ruifeng Wang
>>>>>> <Ruifeng.Wang@arm.com>; viktorin@rehivetech.com;
>>>>>> bruce.richardson@intel.com; Honnappa Nagarahalli
>>>>>> <Honnappa.Nagarahalli@arm.com>; jerinjacobk@gmail.com;
>>>>>> juraj.linkes@pantheon.tech; nd <nd@arm.com>
>>>>>> Subject: [PATCH v6 2/2] net/hns3: refactor SVE code compile method
>>>>>>
>>>>>> Currently, the SVE code is compiled only when -march supports SVE
>>>>>> (e.g. '- march=armv8.2a+sve'), there maybe some problem[1] with
>>>>>> this
>>>> approach.
>>>>>>
>>>>>> The solution:
>>>>>> a. If the minimum instruction set support SVE then compiles it.
>>>>>> b. Else if the compiler support SVE then compiles it.
>>>>>> c. Otherwise don't compile it.
>>>>>>
>>>>>> [1] https://mails.dpdk.org/archives/dev/2021-April/208189.html
>>>>>>
>>>>>> Fixes: 8c25b02b082a ("net/hns3: fix enabling SVE Rx/Tx")
>>>>>> Fixes: 952ebacce4f2 ("net/hns3: support SVE Rx")
>>>>>> Cc: stable@dpdk.org
>>>>>>
>>>>>> Signed-off-by: Chengwen Feng <fengchengwen@huawei.com>
>>>>>> ---
>>>>>>  drivers/net/hns3/hns3_rxtx.c |  2 +-  drivers/net/hns3/meson.build
>>>>>> |
>>>>>> 21 ++++++++++++++++++++-
>>>>>>  2 files changed, 21 insertions(+), 2 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/net/hns3/hns3_rxtx.c
>>>>>> b/drivers/net/hns3/hns3_rxtx.c index 1d7a769..4ef20c6 100644
>>>>>> --- a/drivers/net/hns3/hns3_rxtx.c
>>>>>> +++ b/drivers/net/hns3/hns3_rxtx.c
>>>>>> @@ -2808,7 +2808,7 @@ hns3_get_default_vec_support(void)
>>>>>>  static bool
>>>>>>  hns3_get_sve_support(void)
>>>>>>  {
>>>>>> -#if defined(RTE_ARCH_ARM64) && defined(__ARM_FEATURE_SVE)
>>>>>> +#if defined(CC_SVE_SUPPORT)
>>>>>>  	if (rte_vect_get_max_simd_bitwidth() < RTE_VECT_SIMD_256)
>>>>>>  		return false;
>>>>>>  	if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_SVE))
>>>>>> diff --git a/drivers/net/hns3/meson.build
>>>>>> b/drivers/net/hns3/meson.build index 53c7df7..5f9af9b 100644
>>>>>> --- a/drivers/net/hns3/meson.build
>>>>>> +++ b/drivers/net/hns3/meson.build
>>>>>> @@ -35,7 +35,26 @@ deps += ['hash']
>>>>>>
>>>>>>  if arch_subdir == 'arm' and dpdk_conf.get('RTE_ARCH_64')
>>>>>>      sources += files('hns3_rxtx_vec.c')
>>>>>> -    if cc.get_define('__ARM_FEATURE_SVE', args: machine_args) != ''
>>>>>> +
>>>>>> +    # compile SVE when:
>>>>>> +    # a. support SVE in minimum instruction set baseline
>>>>>> +    # b. it's not minimum instruction set, but compiler support
>>>>>> +    if cc.get_define('__ARM_FEATURE_SVE', args: machine_args) != ''
>>>>>> + and
>>>>>> cc.check_header('arm_sve.h')
>>>>>> +        cflags += ['-DCC_SVE_SUPPORT']
>>>>> With SVE build fix patch [1], CC_SVE_ACLE_SUPPORT will be defined.
>>>>> Here we can use CC_SVE_ACLE_SUPPORT and not to add a new one.
>>>>>
>>>>
>>>> The CC_SVE_ACLE_SUPPORT was defined under default machine_args
>> which
>>>> support SVE, it can't deals with the situation: the default
>>>> machine_args don't support SVE but compiler support SVE.
>>>> So the CC_SVE_SUPPORT marco is necessary.
>>> Agree that macro for SVE is also needed here. And we can also use '-
>> DCC_SVE_ACLE_SUPPORT' here right?
>>> I think there is no difference between CC_SVE_ACLE_SUPPORT and
>> CC_SVE_SUPPORT when they are used in source code.
>>> IMO the same macro name can be used, and it removes redundancy and
>> confusion.
>>>
>>
>> You are right, no difference between CC_SVE_ACLE_SUPPORT and
>> CC_SVE_SUPPORT But the hns3 sve already support 20.11, and
>> CC_SVE_ACLE_SUPPORT was newly defined, there maybe some problems
>> when backporting.
> 20.11 release has no machine enabled SVE extension. 
> 
>>
>> Or we could redefine CC_SVE_ACLE_SUPPORT under default machine_args:
>>     if cc.get_define('__ARM_FEATURE_SVE', args: machine_args) != '' and
>> cc.check_header('arm_sve.h')
>>         cflags += ['-DCC_SVE_ACLE_SUPPORT']
> 'if dpdk_conf.get(CC_SVE_ACLE_SUPPORT)' should be fine?
> Stable branch has no SVE enabled in machine_args.
> 

But 20.11 use could use hns3 SVE path when compile with gcc10.

If we reuse the CC_SVE_ACLE_SUPPORT macro, there maybe problem when backporting:
a. In 21.08 we could depend on CC_SVE_ACLE_SUPPORT, so it will be:
    if dpdk_conf.get('CC_SVE_ACLE_SUPPORT')
        sources += files('hns3_rxtx_vec_sve.c')
    elif cc.has_argument('-march=armv8.2-a+sve') and cc.check_header('arm_sve.h')
        sve_cflags = ['-DCC_SVE_ACLE_SUPPORT']
        ...
b. But for backport to 20.11, we should use another impl:
    if cc.get_define('__ARM_FEATURE_SVE', args: machine_args) != '' and cc.check_header('arm_sve.h')
        cflags += ['-DCC_SVE_ACLE_SUPPORT']
        sources += files('hns3_rxtx_vec_sve.c')
    elif cc.has_argument('-march=armv8.2-a+sve') and cc.check_header('arm_sve.h')
        sve_cflags = ['-DCC_SVE_ACLE_SUPPORT']
        ...
As you see, the above two are not unified.

So here I think use the CC_SVE_SUPPORT is appropriate.

@Ferruh  what's your opinion ?

>>         sources += files('hns3_rxtx_vec_sve.c')
>>     elif cc.has_argument('-march=armv8.2-a+sve') and
>> cc.check_header('arm_sve.h')
>>         sve_cflags = ['-DCC_SVE_ACLE_SUPPORT']
> This is fine. Macro name is consistent.
> 
>>         foreach flag: cflags
>>             # filterout -march -mcpu -mtune
>>             if not (flag.startswith('-march=') or flag.startswith('-mcpu=') or
>> flag.startswith('-mtune='))
>>                 sve_cflags += flag
>>             endif
>>         endforeach
>> but this way may introduce coupling, I think.
>>
>>>>
>>>>> [1]
>>>>> http://patches.dpdk.org/project/dpdk/patch/1621495007-28387-1-git-se
>>>>> nd
>>>>> -email-fengchengwen@huawei.com/
>>>>>
>>>>>>          sources += files('hns3_rxtx_vec_sve.c')
>>>>>> +    elif cc.has_argument('-march=armv8.2-a+sve') and
>>>>>> cc.check_header('arm_sve.h')
>>>>>> +        sve_cflags = ['-DCC_SVE_SUPPORT']
>>>>>> +        foreach flag: cflags
>>>>>> +            # filterout -march -mcpu -mtune
>>>>>> +            if not (flag.startswith('-march=') or
>>>>>> + flag.startswith('-mcpu=') or
>>>>>> flag.startswith('-mtune='))
>>>>>> +                sve_cflags += flag
>>>>>> +            endif
>>>>>> +        endforeach
>>>>>> +        hns3_sve_lib = static_library('hns3_sve_lib',
>>>>>> +                        'hns3_rxtx_vec_sve.c',
>>>>>> +                        dependencies: [static_rte_ethdev],
>>>>>> +                        include_directories: includes,
>>>>>> +                        c_args: [sve_cflags, '-march=armv8.2-a+sve'])
>>>>>> +        objs +=
>>>>>> + hns3_sve_lib.extract_objects('hns3_rxtx_vec_sve.c')
>>>>>>      endif
>>>>>>  endif
>>>>>> --
>>>>>> 2.8.1
>>>>>
>>>>>
>>>>> .
>>>>>
>>>
>