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

[Jerin Jacob Kollanukkaran <jerinj@marvell.com>]

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?

> 
> > > Signed-off-by: Yongseok Koh <yskoh@mellanox.com>
> > > ---
> > > 
> > > Discussion on the mailing list:
> > >     https://mails.dpdk.org/archives/dev/2019-January/122441.html
> > > 
> > >  config/arm/meson.build | 11 +++++++----
> > >  1 file changed, 7 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/config/arm/meson.build b/config/arm/meson.build
> > > index dae55d6b26..3af256a5ec 100644
> > > --- a/config/arm/meson.build
> > > +++ b/config/arm/meson.build
> > > @@ -47,8 +47,7 @@ flags_common_default = [
> > >  flags_generic = [
> > >  	['RTE_MACHINE', '"armv8a"'],
> > >  	['RTE_MAX_LCORE', 256],
> > > -	['RTE_USE_C11_MEM_MODEL', true],
> > > -	['RTE_CACHE_LINE_SIZE', 128]]
> > > +	['RTE_USE_C11_MEM_MODEL', true]]
> > >  flags_cavium = [
> > >  	['RTE_MACHINE', '"thunderx"'],
> > >  	['RTE_CACHE_LINE_SIZE', 128],
> > > @@ -89,15 +88,19 @@ impl_dpaa2 = ['NXP DPAA2', flags_dpaa2,
> > > machine_args_generic]
> > >  
> > >  dpdk_conf.set('RTE_FORCE_INTRINSICS', 1)
> > >  
> > > +# 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.
> > > +dpdk_conf.set('RTE_CACHE_LINE_SIZE', 64)
> > > +
> > >  if cc.sizeof('void *') != 8
> > > -	dpdk_conf.set('RTE_CACHE_LINE_SIZE', 64)
> > >  	dpdk_conf.set('RTE_ARCH_ARM', 1)
> > >  	dpdk_conf.set('RTE_ARCH_ARMv7', 1)
> > >  	# the minimum architecture supported, armv7-a, needs the
> > > following,
> > >  	# mk/machine/armv7a/rte.vars.mk sets it too
> > >  	machine_args += '-mfpu=neon'
> > >  else
> > > -	dpdk_conf.set('RTE_CACHE_LINE_SIZE', 128)
> > >  	dpdk_conf.set('RTE_ARCH_ARM64', 1)
> > >  	dpdk_conf.set('RTE_ARCH_64', 1)
> > >