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

[Ruifeng Wang <Ruifeng.Wang@arm.com>]

> -----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.

>         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
> >>>
> >>>
> >>> .
> >>>
> >