Re: [dpdk-dev] [PATCH v8 2/4] meson: add infra to support machine specific flags

[Pavan Nikhilesh Bhagavatula <pbhagavatula@marvell.com>]

Hi Yongseok,

>-----Original Message-----
>From: Yongseok Koh <yskoh@mellanox.com>
>Sent: Wednesday, April 10, 2019 11:08 PM
>To: Pavan Nikhilesh Bhagavatula <pbhagavatula@marvell.com>
>Cc: Thomas Monjalon <thomas@monjalon.net>; dev <dev@dpdk.org>; Jerin
>Jacob Kollanukkaran <jerinj@marvell.com>; jerinjacobk@gmail.com
>Subject: [EXT] Re: [dpdk-dev] [PATCH v8 2/4] meson: add infra to support
>machine specific flags
>
>External Email
>
>----------------------------------------------------------------------
>
>> On Apr 10, 2019, at 9:13 AM, jerinjacobk@gmail.com wrote:
>>
>> From: Pavan Nikhilesh <pbhagavatula@marvell.com>
>>
>> Currently, RTE_* flags are set based on the implementer ID but there
>> might be some micro arch specific differences from the same vendor eg.
>> CACHE_LINESIZE. Add support to set micro arch specific flags.
>>
>> Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
>> Signed-off-by: Jerin Jacob <jerinj@marvell.com>
>> ---
>> config/arm/meson.build | 56 ++++++++++++++++++++++++------------------
>> 1 file changed, 32 insertions(+), 24 deletions(-)
>>
>> diff --git a/config/arm/meson.build b/config/arm/meson.build index
>> 170a4981a..24bce2b39 100644
>> --- a/config/arm/meson.build
>> +++ b/config/arm/meson.build
>> @@ -7,25 +7,6 @@ march_opt = '-march=@0@'.format(machine)
>>
>> arm_force_native_march = false
>>
>> -machine_args_generic = [
>> -	['default', ['-march=armv8-a+crc+crypto']],
>> -	['native', ['-march=native']],
>> -	['0xd03', ['-mcpu=cortex-a53']],
>> -	['0xd04', ['-mcpu=cortex-a35']],
>> -	['0xd05', ['-mcpu=cortex-a55']],
>> -	['0xd07', ['-mcpu=cortex-a57']],
>> -	['0xd08', ['-mcpu=cortex-a72']],
>> -	['0xd09', ['-mcpu=cortex-a73']],
>> -	['0xd0a', ['-mcpu=cortex-a75']],
>> -	['0xd0b', ['-mcpu=cortex-a76']],
>> -]
>> -machine_args_cavium = [
>> -	['default', ['-march=armv8-a+crc+crypto','-mcpu=thunderx']],
>> -	['native', ['-march=native']],
>> -	['0xa1', ['-mcpu=thunderxt88']],
>> -	['0xa2', ['-mcpu=thunderxt81']],
>> -	['0xa3', ['-mcpu=thunderxt83']]]
>> -
>> flags_common_default = [
>> 	# Accelarate rte_memcpy. Be sure to run unit test
>(memcpy_perf_autotest)
>> 	# to determine the best threshold in code. Refer to notes in source
>> file @@ -52,12 +33,10 @@ flags_generic = [
>> 	['RTE_USE_C11_MEM_MODEL', true],
>> 	['RTE_CACHE_LINE_SIZE', 128]]
>> flags_cavium = [
>> -	['RTE_MACHINE', '"thunderx"'],
>> 	['RTE_CACHE_LINE_SIZE', 128],
>> 	['RTE_MAX_NUMA_NODES', 2],
>> 	['RTE_MAX_LCORE', 96],
>> -	['RTE_MAX_VFIO_GROUPS', 128],
>> -	['RTE_USE_C11_MEM_MODEL', false]]
>> +	['RTE_MAX_VFIO_GROUPS', 128]]
>> flags_dpaa = [
>> 	['RTE_MACHINE', '"dpaa"'],
>> 	['RTE_USE_C11_MEM_MODEL', true],
>> @@ -71,6 +50,27 @@ flags_dpaa2 = [
>> 	['RTE_MAX_NUMA_NODES', 1],
>> 	['RTE_MAX_LCORE', 16],
>> 	['RTE_LIBRTE_DPAA2_USE_PHYS_IOVA', false]]
>> +flags_default_extra = []
>> +flags_thunderx_extra = [
>> +	['RTE_MACHINE', '"thunderx"'],
>> +	['RTE_USE_C11_MEM_MODEL', false]]
>> +
>> +machine_args_generic = [
>> +	['default', ['-march=armv8-a+crc+crypto']],
>> +	['native', ['-march=native']],
>> +	['0xd03', ['-mcpu=cortex-a53']],
>> +	['0xd04', ['-mcpu=cortex-a35']],
>> +	['0xd07', ['-mcpu=cortex-a57']],
>> +	['0xd08', ['-mcpu=cortex-a72']],
>> +	['0xd09', ['-mcpu=cortex-a73']],
>> +	['0xd0a', ['-mcpu=cortex-a75']]]
>> +
>> +machine_args_cavium = [
>> +	['default', ['-march=armv8-a+crc+crypto','-mcpu=thunderx']],
>> +	['native', ['-march=native']],
>> +	['0xa1', ['-mcpu=thunderxt88'], flags_thunderx_extra],
>> +	['0xa2', ['-mcpu=thunderxt81'], flags_thunderx_extra],
>> +	['0xa3', ['-mcpu=thunderxt83'], flags_thunderx_extra]]
>>
>> ## Arm implementer ID (ARM DDI 0487C.a, Section G7.2.106, Page
>> G7-5321) impl_generic = ['Generic armv8', flags_generic,
>> machine_args_generic] @@ -157,8 +157,16 @@ else
>> 	endif
>> 	foreach marg: machine[2]
>> 		if marg[0] == impl_pn
>> -			foreach f: marg[1]
>> -				machine_args += f
>> +			foreach flag: marg[1]
>> +				if cc.has_argument(flag)
>> +					machine_args += flag
>> +				endif
>> +			endforeach
>> +			# Apply any extra machine specific flags.
>> +			foreach flag: marg.get(2, flags_default_extra)
>> +				if flag.length() > 0
>> +					dpdk_conf.set(flag[0], flag[1])
>> +				endif
>
>Let me continue the discussion from v7 here.
>Seems I wan't clear enough.
>
>Let me take an example. If the host is thunderx2 (0xaf) and compiler is older
>than v7, flags_thunderx2_extra isn't set. This means, for example,
>RTE_CACHE_LINE_SIZE will still be 128. Is that what you want?
>RTE_CACHE_LINE_SIZE has nothing to do with compiler support and you might
>want to set it regardless of gcc version. You could skip setting -mcpu with setting
>the extra flags.
>

Thanks for the detailed explanation.
I think since we have the check to skip mcpu flag when cc doesn't support it (cc.has_argument(flag))
It will be safe to remove 
`
        # Primary part number based mcpu flags are supported
        # for gcc versions > 7
        if cc.version().version_compare(
                        '<7.0') or cmd_output.length() == 0
                if not meson.is_cross_build() and arm_force_native_march == true
                        impl_pn = 'native'
                else
                        impl_pn = 'default'
                endif
        endif
`

The command output check can also be removed as it is handled when calling the command script itself.

Thoughts?

PS. I think the safest way to set CACHELINE_SIZE is to read the cache type register[1] but sadly only few latest kernels 
have the support through sysfs (/sys/devices/system/cpu/cpu0/cache/index0/coherency_line_size) 

>Thoughts?
>
>Thanks,
>Yongseok
>
>
>

Regards,
Pavan.