Re: [dpdk-dev] [PATCH v4 3/3] build: add option to enable wait until equal

[Jerin Jacob <jerinjacobk@gmail.com>]

On Thu, Jul 8, 2021 at 11:55 AM Ruifeng Wang <Ruifeng.Wang@arm.com> wrote:
>
> > -----Original Message-----
> > From: Jerin Jacob <jerinjacobk@gmail.com>
> > Sent: Wednesday, July 7, 2021 8:37 PM
> > To: Bruce Richardson <bruce.richardson@intel.com>
> > Cc: Ruifeng Wang <Ruifeng.Wang@arm.com>; thomas@monjalon.net; Jan
> > Viktorin <viktorin@rehivetech.com>; jerinj@marvell.com; dev@dpdk.org;
> > david.marchand@redhat.com; nd <nd@arm.com>; Honnappa Nagarahalli
> > <Honnappa.Nagarahalli@arm.com>
> > Subject: Re: [dpdk-dev] [PATCH v4 3/3] build: add option to enable wait until
> > equal
> >
> > On Wed, Jul 7, 2021 at 5:57 PM Bruce Richardson
> > <bruce.richardson@intel.com> wrote:
> > >
> > > On Wed, Jul 07, 2021 at 06:46:33AM +0000, Ruifeng Wang wrote:
> > > > > -----Original Message-----
> > > > > From: Thomas Monjalon <thomas@monjalon.net>
> > > > > Sent: Wednesday, July 7, 2021 2:32 PM
> > > > > To: Ruifeng Wang <Ruifeng.Wang@arm.com>
> > > > > Cc: Jan Viktorin <viktorin@rehivetech.com>; jerinj@marvell.com;
> > > > > Bruce Richardson <bruce.richardson@intel.com>; dev@dpdk.org;
> > > > > david.marchand@redhat.com; nd <nd@arm.com>; Honnappa
> > Nagarahalli
> > > > > <Honnappa.Nagarahalli@arm.com>
> > > > > Subject: Re: [PATCH v4 3/3] build: add option to enable wait until
> > > > > equal
> > > > >
> > > > > 07/07/2021 07:48, Ruifeng Wang:
> > > > > > Introduce a meson option 'use_wfe' to select wait until equal method.
> > > > > > The default is disable. Traditional polling loop is used.
> > > > > > When enabled, architecture specific mechanism is relied on to do
> > > > > > the wait.
> > > > >
> > > > > Why do we need an option?
> > > > > Can it be automatic to enable it when supported?
> > > > >
> > > > The problem is inconsistency in performance on different Arm platforms.
> > We had decided that each platform needs to enable it after some testing.
> > > >
> > > Can that not be done via variables in the cross-file for the builds,
> > > or via automatic detection if it's a native build? Is it likely that
> > > individual users of DPDK will be knowledgable enough to use this option
> > correctly?
> >
> > +1 to add this in cross-file instead of the top of config option as
> > scope if is only for arm64 builds.
>
> Currently this option is in config/arm/meson.build (flags_common). SoCs can build
> with this option enabled/disabled. And the ability is available for both native build
> and cross build as cross build also goes through meson.build.
> If a SoC needs to enable the option by default, an entry and be added to the SoC flags.
>
> The key difference here is whether this option need to be exposed to the top level config.

In the view of limiting top-level config options and it is specific to
Arm, I think, it better to
be a cross file only option.