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

[Ruifeng Wang <Ruifeng.Wang@arm.com>]

> -----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.