[dpdk-dev] [PATCH 2/2] build: find max lcore programmatically

[Dharmik Thakkar]

Hi Juraj,

> On Oct 13, 2020, at 9:58 AM, Juraj Linkeš <juraj.linkes at pantheon.tech> wrote:
> 
> I believe we're going to drop this patch series in favor of http://patches.dpdk.org/project/dpdk/list/?series=12923.

I can see you have included this feature in your series. Thank you!
What are your thoughts on the other patch [1]? Do you plan on including that as well in your series?

[1] 	[1/2] config/arm: avoid variable reuse
https://patches.dpdk.org/patch/75946/

> 
>> -----Original Message-----
>> From: Thomas Monjalon <thomas at monjalon.net>
>> Sent: Tuesday, October 13, 2020 4:32 PM
>> To: Dharmik Thakkar <Dharmik.Thakkar at arm.com>
>> Cc: Juraj Linkeš <juraj.linkes at pantheon.tech>; dev at dpdk.org; Stephen
>> Hemminger <stephen at networkplumber.org>; Jerin Jacob
>> <jerinjacobk at gmail.com>; nd <nd at arm.com>
>> Subject: Re: [dpdk-dev] [PATCH 2/2] build: find max lcore programmatically
>> 
>> Please, what is the conclusion here?
>> 
>> 
>> 18/09/2020 07:47, Dharmik Thakkar:
>>> 
>>>> On Sep 17, 2020, at 4:56 AM, Juraj Linkeš <juraj.linkes at pantheon.tech>
>> wrote:
>>>> 
>>>> 
>>>> 
>>>>> -----Original Message-----
>>>>> From: Dharmik Thakkar <Dharmik.Thakkar at arm.com>
>>>>> Sent: Friday, September 4, 2020 7:44 AM
>>>>> To: Stephen Hemminger <stephen at networkplumber.org>
>>>>> Cc: Juraj Linkeš <juraj.linkes at pantheon.tech>; Jerin Jacob
>>>>> <jerinjacobk at gmail.com>; thomas at monjalon.net; dpdk-dev
>>>>> <dev at dpdk.org>; nd <nd at arm.com>
>>>>> Subject: Re: [dpdk-dev] [PATCH 2/2] build: find max lcore
>>>>> programmatically
>>>>> 
>>>>> 
>>>>> 
>>>>>> On Sep 3, 2020, at 5:52 PM, Stephen Hemminger
>>>>> <stephen at networkplumber.org> wrote:
>>>>>> 
>>>>>> On Thu, 3 Sep 2020 06:20:17 +0000
>>>>>> Juraj Linkeš <juraj.linkes at pantheon.tech> wrote:
>>>>>> 
>>>>>>>> -----Original Message-----
>>>>>>>> From: dev <dev-bounces at dpdk.org> On Behalf Of Dharmik Thakkar
>>>>>>>> Sent: Wednesday, August 26, 2020 6:56 AM
>>>>>>>> To: Jerin Jacob <jerinjacobk at gmail.com>
>>>>>>>> Cc: thomas at monjalon.net; dpdk-dev <dev at dpdk.org>; nd
>>>>>>>> <nd at arm.com>
>>>>>>>> Subject: Re: [dpdk-dev] [PATCH 2/2] build: find max lcore
>>>>>>>> programmatically
>>>>>>>> 
>>>>>>>> 
>>>>>>>> 
>>>>>>>>> On Aug 25, 2020, at 11:47 PM, Jerin Jacob
>>>>>>>>> <jerinjacobk at gmail.com>
>>>>> wrote:
>>>>>>>>> 
>>>>>>>>> On Wed, Aug 26, 2020 at 2:44 AM Dharmik Thakkar
>>>>>>>> <dharmik.thakkar at arm.com> wrote:
>>>>>>>>>> 
>>>>>>>>>> For Arm, RTE_MAX_LCORE is hard-coded into the config. It leads
>>>>>>>>>> to incorrect RTE_MAX_LCORE when machines have same
>> Implemener
>>>>>>>>>> and part number but different number of CPUs.
>>>>>>>>>> For x86, RTE_MAX_LCORE is always set to 128 (using the value
>>>>>>>>>> set in
>>>>>>>>>> meson_options.txt)
>>>>>>>>>> 
>>>>>>>>>> Use python script to find max lcore when using native build to
>>>>>>>>>> correctly set RTE_MAX_LCORE.
>>>>>>>>> 
>>>>>>>>> We may need to build on the native arm64 machine and use it on
>>>>>>>>> another
>>>>>>>>> arm64 machine(Just like x86).
>>>>>>>>> So I think, at least for default config(which will be used by
>>>>>>>>> distribution) to support max
>>>>>>>>> lcores as fixed. I am not sure this patch changes those aspects
>>>>>>>>> or not? Please check.
>>>>>>>> 
>>>>>>>> This patch does *not* affect ‘default’ build type and cross-compilation.
>>>>>>>> 
>>>>>>>>> 
>>>>>>>>>> 
>>>>>>>>>> Signed-off-by: Dharmik Thakkar <dharmik.thakkar at arm.com>
>>>>>>>>>> Reviewed-by: Ruifeng Wang <ruifeng.wang at arm.com>
>>>>>>>>>> ---
>>>>>>>>>> config/get_max_lcores.py | 13 +++++++++++++
>>>>>>>>>> config/meson.build       | 13 ++++++++++++-
>>>>>>>>>> 2 files changed, 25 insertions(+), 1 deletion(-) create mode
>>>>>>>>>> 100755 config/get_max_lcores.py
>>>>>>>>>> 
>>>>>>>>>> diff --git a/config/get_max_lcores.py
>>>>>>>>>> b/config/get_max_lcores.py new file mode 100755 index
>>>>>>>>>> 000000000000..ebf1c7efdadd
>>>>>>>>>> --- /dev/null
>>>>>>>>>> +++ b/config/get_max_lcores.py
>>>>>>>>>> @@ -0,0 +1,13 @@
>>>>>>>>>> +#!/usr/bin/python3
>>>>>>>>>> +# SPDX-License-Identifier: BSD-3-Clause # Copyright(c) 2020
>>>>>>>>>> +Arm Limited
>>>>>>>>>> +
>>>>>>>>>> +import os
>>>>>>>>>> +
>>>>>>>>>> +max_lcores = []
>>>>>>>>>> +
>>>>>>>>>> +nCPU = os.cpu_count()
>>>>>>>>>> +
>>>>>>>>>> +max_lcores.append(str(nCPU & 0xFFF))             # Number of CPUs
>>>>>>>>>> +
>>>>>>>>>> +print(' '.join(max_lcores))
>>>>>>>>>> diff --git a/config/meson.build b/config/meson.build index
>>>>>>>>>> 6996e5cbeaa5..80c05bc15d2f 100644
>>>>>>>>>> --- a/config/meson.build
>>>>>>>>>> +++ b/config/meson.build
>>>>>>>>>> @@ -237,11 +237,22 @@ else # for 32-bit we need smaller
>>>>>>>>>> reserved memory
>>>>>>>> areas
>>>>>>>>>>     dpdk_conf.set('RTE_MAX_MEM_MB', 2048) endif
>>>>>>>>>> 
>>>>>>>>>> -
>>>>>>>>>> compile_time_cpuflags = []
>>>>>>>>>> subdir(arch_subdir)
>>>>>>>>>> dpdk_conf.set('RTE_COMPILE_TIME_CPUFLAGS',
>>>>>>>>>> ','.join(compile_time_cpuflags))
>>>>>>>>>> 
>>>>>>>>>> +# set max lcores
>>>>>>>>>> +if machine != 'default' and not meson.is_cross_build()
>>>>>>>>>> +       # The script returns max lcores
>>>>>>>>>> +       params = files('get_max_lcores.py')
>>>>>>>>>> +       cmd_out = run_command(params)
>>>>>>> 
>>>>>>> Have you considered running just a shell command, such as "nproc --all"?
>>>>>> 
>>>>>> Is this really a good idea?
>>>>>> For real distributions and NFV products, the build and runtime
>>>>>> environment will usually be different even if on same CPU architecture.
>>>>>> 
>>>>>> In many cases there maybe a huge build machine (128 CPU) or in a
>>>>>> container (reported as single cpu) even if not doing cross build.
>>>>> 
>>>>> That’s a great point, Stephen. IMO, this patch is useful when
>>>>> building and running natively.
>>>>> For all other purposes (like the ones you mentioned), do you think
>>>>> it is a good idea to set RTE_MAX_LCORE using -Dmax_lcores?
>>>> 
>>>> We should only use this native builds, as that would be consistent with the
>> current meson build philosophy of "meson figuring as much as possible on its
>> own". Any build other than native implies the user wants to deviate from the
>> build machine.
>>>> 
>>> 
>>> The MIDR value-based probing doesn’t quite work well for Arm IP (currently
>> being discussed on this patch: https://patches.dpdk.org/patch/76981/).
>>> 
>>>> One way to do this automatic core count is when max_lcores=0 (0 would
>> have the special meaning of "figure core count automatically"). We can set that
>> as default in meson_option.txt and then users will have the ability to set it to
>> whatever they want, even for native builds. What do you think?
>>>> 
>>> 
>>> Yes, agreed.
>>> 
>>>> Currently the -Dmax_lcores option doesn't work for arm builds (the value of
>> RTE_MAX_LCORE is overwritten in config/arm/meson.build). I believe the patch
>> tries to address this, but still, we need to be mindful of that.
>>>> 
>>>> Juraj
>> 
>> 
>