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

[Dharmik Thakkar <Dharmik.Thakkar@arm.com>]

> On Sep 3, 2020, at 5:52 PM, Stephen Hemminger <stephen@networkplumber.org> wrote:
> 
> On Thu, 3 Sep 2020 06:20:17 +0000
> Juraj Linkeš <juraj.linkes@pantheon.tech> wrote:
> 
>>> -----Original Message-----
>>> From: dev <dev-bounces@dpdk.org> On Behalf Of Dharmik Thakkar
>>> Sent: Wednesday, August 26, 2020 6:56 AM
>>> To: Jerin Jacob <jerinjacobk@gmail.com>
>>> Cc: thomas@monjalon.net; dpdk-dev <dev@dpdk.org>; nd <nd@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@gmail.com> wrote:
>>>> 
>>>> On Wed, Aug 26, 2020 at 2:44 AM Dharmik Thakkar  
>>> <dharmik.thakkar@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@arm.com>
>>>>> Reviewed-by: Ruifeng Wang <ruifeng.wang@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?