Re: [EXT] [PATCH] config: change default cache line size for ARMv8 with meson

[Luca Boccassi <bluca@debian.org>]

On Wed, 2019-01-09 at 10:52 +0000, Jerin Jacob Kollanukkaran wrote:
> On Wed, 2019-01-09 at 10:19 +0000, Luca Boccassi wrote:
> > On Wed, 2019-01-09 at 10:09 +0000, Jerin Jacob Kollanukkaran wrote:
> > > On Wed, 2019-01-09 at 01:39 -0800, Yongseok Koh wrote:
> > > > ---------------------------------------------------------------
> > > > ----
> > > > ---
> > > > In config/arm64_armv8_linuxapp_gcc, maximum available cache
> > > > line
> > > > size
> > > > (128B) in arm64 implementations is set by default for generic
> > > > config.
> > > > However, setting 64B is preferable for meson build in order to
> > > > support
> > > > majority of CPUs which don't have Implementor ID or Part Number
> > > > programmed
> > > > on chip.
> > > 
> > > Adding Luca to get input from distro build perspective.
> > > 
> > > If I understand it correctly, distro build will be using
> > > the generic config/arm/arm64_armv8_linuxapp_gcc for generic
> > > build.
> > > If so, We can not change cache line size for generic config
> > > as mentined the reason are
> > > https://mails.dpdk.org/archives/dev/2019-January/122441.html
> > > 
> > > 
> > > I think, I way forward is to add
> > > config/arm/arm64_a72_linuxapp_gcc
> > > for meson. This config can be used for all SoC with A72 armv8 
> > > implementation and may have sym link to specfific SoC to avoid
> > > confusion to end users.
> > 
> > For Meson, I recently sent a patch to use a common and stable
> > baseline
> > machine arg if the uses sets it to "default":
> > 
> > https://patches.dpdk.org/patch/49477/
> > 
> > For distros, I think if, within that path, the cache size is set to
> > the
> > minimum common denominator like the -march is, it will be fine.
> > 
> > At that point, what happens for "native" or otherwise specified
> > builds
> > it will not affect distros (as long as they use "default" like
> > Debian
> > and Ubuntu do).
> > 
> 
> Thanks for the input
> 
> > Does this answer your question?
> 
> 
> Kind of.. Will you be building "the generic image" on ANY arm64
> machine
> with following command?
> 
> meson configure -Dmachine=default
> meson build
> cd build
> ninja
> ninja install
> 
> If so, This patch will change the cache line size of generic build.
> Right?

Yes, that's the command used everywhere on Debian/Ubuntu, regardless of
the machine type, and this patch will change the value for those cases
as far as I can see.

Please bear in mind that I know really little about arm, so I am not
sure which should be the default for maximum compatibility.

-- 
Kind regards,
Luca Boccassi