Re: [dpdk-dev] [EXT] Re: [PATCH v5 1/3] net/thunderx: enable build only on 64-bit Linux

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

>-----Original Message-----
>From: Ferruh Yigit <ferruh.yigit@intel.com>
>Sent: Monday, October 11, 2021 5:11 PM
>To: Jerin Jacob <jerinjacobk@gmail.com>
>Cc: Pavan Nikhilesh Bhagavatula <pbhagavatula@marvell.com>; Jerin
>Jacob Kollanukkaran <jerinj@marvell.com>; Maciej Czekaj [C]
><mczekaj@marvell.com>; dev@dpdk.org; Bruce Richardson
><bruce.richardson@intel.com>
>Subject: Re: [dpdk-dev] [EXT] Re: [PATCH v5 1/3] net/thunderx: enable
>build only on 64-bit Linux
>
>On 10/10/2021 10:38 AM, Jerin Jacob wrote:
>> On Fri, Oct 8, 2021 at 9:00 PM Ferruh Yigit <ferruh.yigit@intel.com>
>wrote:
>>>
>>> On 10/4/2021 1:54 PM, Pavan Nikhilesh Bhagavatula wrote:
>>>>> On 10/4/2021 1:01 PM, Pavan Nikhilesh Bhagavatula wrote:
>>>>>>> On 10/4/2021 12:34 PM, Pavan Nikhilesh Bhagavatula wrote:
>>>>>>>>> On 10/4/2021 11:02 AM, Pavan Nikhilesh Bhagavatula wrote:
>>>>>>>>>>> On 10/4/2021 6:56 AM, pbhagavatula@marvell.com
>wrote:
>>>>>>>>>>>> From: Pavan Nikhilesh <pbhagavatula@marvell.com>
>>>>>>>>>>>>
>>>>>>>>>>>> Due to Linux kernel AF(Admin function) driver
>dependency,
>>>>> only
>>>>>>>>>>> enable
>>>>>>>>>>>> build for 64-bit Linux.
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Hi Pavan,
>>>>>>>>>>>
>>>>>>>>>>> Isn't it possible to provide a commit log in the kernel side
>etc,
>>>>> that
>>>>>>> let
>>>>>>>>>>> others to verify why only 64 bit is required, or if someone
>want
>>>>> to
>>>>>>>>>>> support
>>>>>>>>>>> 32bit that may help them to investigate the source of the
>>>>>>> restriction.
>>>>>>>>>>
>>>>>>>>>> Arch 32 support is not implemented on ThunderX, so 32bit
>will
>>>>> not
>>>>>>>>> run.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> I see, is following correct:
>>>>>>>>> All thunderx, octeonx & octeontx2 only supports VF in the
>DPDK,
>>>>>>> and PF
>>>>>>>>> is
>>>>>>>>> supported by Linux kernel driver. And Linux kernel driver
>doesn't
>>>>>>>>> support arch32.
>>>>>>>>
>>>>>>>> AF != PF, AF is something that manages all the shared
>resources
>>>>>>> between PF/VF.
>>>>>>>>
>>>>>>>
>>>>>>> I see, I though AF is part of PF functionality. Are there two
>different
>>>>>>> kernel
>>>>>>> modules for PF and AF?
>>>>>>>
>>>>>>> So can DPDK driver drive PF? In a way, PF by DPDK, VF by DPDK,
>AF
>>>>> by
>>>>>>> Linux
>>>>>>> kernel driver.
>>>>>>
>>>>>> Yup that’s correct.
>>>>>>
>>>>>>>
>>>>>>>>>
>>>>>>>>> Is something changed in kernel driver side to drop the 32bit
>>>>> support?
>>>>>>>>> If it was not supported at all, what is the motivation to
>disable the
>>>>>>> DPDK
>>>>>>>>> drivers now?
>>>>>>>>>
>>>>>>>>
>>>>>>>> It was never supported to begin with, motivation is that build
>will
>>>>> fail if
>>>>>>> we try to
>>>>>>>> compile with 32b.
>>>>>>>>
>>>>>>>
>>>>>>> If there is no plan to support 32bit in the kernel side, that is
>>>>> reasonable
>>>>>>> to
>>>>>>> disable 32bit build, please provide above details in the commit
>log.
>>>>>>>
>>>>>>> And after above said, how much maintenance cost to support
>32bit,
>>>>> if
>>>>>>> the build
>>>>>>> error is on the logging format "%lx" etc .. (as we mostly have
>32bit
>>>>> build
>>>>>>> errors), it is better to fix them using 'PRIx64' which is more
>proper
>>>>> way
>>>>>>> anyway. If there is more logical issue with 32bit pointers, I
>agree with
>>>>>>> you to
>>>>>>> disable it.
>>>>>>> Can you please provided the build error in the commit log as
>record?
>>>>>>>
>>>>>>
>>>>>> Apologies, I meant that all the functions that don’t fall under 64b
>are
>>>>> stubbed out
>>>>>> so the driver wouldn’t work.
>>>>>>
>>>>>
>>>>> so is there build error or not?
>>>>>
>>>>
>>>> No build error.
>>>>
>>>
>>> Just trying to clarify,
>>>
>>> Linux kernel AF kernel driver only build for 64-bit Linux.
>>> And mentioned DPDK drivers have a dependency to this kernel
>module.
>>>
>>> But DPDK drivers are userspace application, can't 32-bit application
>>> run on 64-bit Linux?
>>>
>>> Can you please clarify what exactly is not supported?
>>
>>
>> armv8 specification has two operating modes,
>>
>> 1) AArch32 mode, where a 32 bit application can run on armv8
>> 2) AArch64 mode, where it is native 64bit support.
>>
>> In Thunderx and Octeon families, AArch32 mode is not implemented
>to save
>> the power and RTL cost. So it can never use AArch32 32bit mode.
>>
>> There was an attempt to emulate 32bit mode in 64 bit like X32_ABI, it
>> is called IPL32 in arm64, that never became mainstream. So 32bit
>application
>> can not run on ThunderX/Octeontx so we would like to remove
>building this option
>> to avoid removing the cost of maintaining it.
>>
>>
>
>Thanks for the clarification, so main motivation is not the AF driver
>dependency?
>
>Can you please put above description to the commit log in next version?

Sure, I will send the next version.

>
>Thanks,
>Ferruh

Thanks,
Pavan.

>
>>
>>>
>>>
>>>>>>>>>>>
>>>>>>>>>>>> Signed-off-by: Pavan Nikhilesh
><pbhagavatula@marvell.com>
>>>>>>>>>>>> Acked-by: Jerin Jacob <jerinj@marvell.com>
>>>>>>>>>>>> ---
>>>>>>>>>>>>    v5 Changes
>>>>>>>>>>>>    - s/fuction/function.
>>>>>>>>>>>>
>>>>>>>>>>>>    v4 Changes:
>>>>>>>>>>>>    - Update commit message regarding dependency on
>AF
>>>>> driver.
>>>>>>>>>>>>
>>>>>>>>>>>>    drivers/net/thunderx/meson.build | 4 ++--
>>>>>>>>>>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>>>>>>>>>>
>>>>>>>>>>>> diff --git a/drivers/net/thunderx/meson.build
>>>>>>>>>>> b/drivers/net/thunderx/meson.build
>>>>>>>>>>>> index 4bbcea7f93..da665bd76f 100644
>>>>>>>>>>>> --- a/drivers/net/thunderx/meson.build
>>>>>>>>>>>> +++ b/drivers/net/thunderx/meson.build
>>>>>>>>>>>> @@ -1,9 +1,9 @@
>>>>>>>>>>>>    # SPDX-License-Identifier: BSD-3-Clause
>>>>>>>>>>>>    # Copyright(c) 2017 Cavium, Inc
>>>>>>>>>>>>
>>>>>>>>>>>> -if is_windows
>>>>>>>>>>>> +if not is_linux or not dpdk_conf.get('RTE_ARCH_64')
>>>>>>>>>>>>        build = false
>>>>>>>>>>>> -    reason = 'not supported on Windows'
>>>>>>>>>>>> +    reason = 'only supported on 64-bit Linux'
>>>>>>>>>>>>        subdir_done()
>>>>>>>>>>>>    endif
>>>>>>>>>>>>
>>>>>>>>>>>> --
>>>>>>>>>>>> 2.17.1
>>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>
>>>>>>
>>>>
>>>