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

["Juraj Linkeš" <juraj.linkes@pantheon.tech>]

I believe we're going to drop this patch series in favor of http://patches.dpdk.org/project/dpdk/list/?series=12923. 

> -----Original Message-----
> From: Thomas Monjalon <thomas@monjalon.net>
> Sent: Tuesday, October 13, 2020 4:32 PM
> To: Dharmik Thakkar <Dharmik.Thakkar@arm.com>
> Cc: Juraj Linkeš <juraj.linkes@pantheon.tech>; dev@dpdk.org; Stephen
> Hemminger <stephen@networkplumber.org>; Jerin Jacob
> <jerinjacobk@gmail.com>; nd <nd@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@pantheon.tech>
> wrote:
> > >
> > >
> > >
> > >> -----Original Message-----
> > >> From: Dharmik Thakkar <Dharmik.Thakkar@arm.com>
> > >> Sent: Friday, September 4, 2020 7:44 AM
> > >> To: Stephen Hemminger <stephen@networkplumber.org>
> > >> Cc: Juraj Linkeš <juraj.linkes@pantheon.tech>; Jerin Jacob
> > >> <jerinjacobk@gmail.com>; 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 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?
> > >
> > > 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
> 
>