Re: [dpdk-dev] [EXT] Default cacheline size for ARM

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

On Wed, 2019-01-23 at 16:28 +0000, Honnappa Nagarahalli wrote:
> > On Fri, 2019-01-18 at 05:50 +0000, Honnappa Nagarahalli wrote:
> > > > > > > > > > Hi,
> > > > > > > > > > 
> > > > > > > > > > The cacheline size (RTE_CACHE_LINE_SIZE) for ARM
> > > > > > > > > > CPUs is
> > > > > > > > > > set to be 128B by default. Mellanox's BlueField is
> > > > > > > > > > an
> > > > > > > > > > ARM CPU having
> > > > > > > > > > Cortex-A72
> > > > > > > > > > and its CL size is 64B.
> > > > > > > > Just wondering how many devices are out there with 128B
> > > > > > > > cache line? I also have not heard about any future
> > > > > > > > devices
> > > > > > > > with 128B cache line. If the majority is 64B, why not
> > > > > > > > keep
> > > > > > > > 64B as the default?
> > > > > > > 
> > > > > > > The problem is, In the armv8 spec the cache line size is
> > > > > > > IMPLEMENTATION DEFINED. Marvell's embedded processors has
> > 128B
> > > > CL
> > > > > > > and Server processors has 64B CL.
> > > > > > > 
> > > > > > > Assuming the defconfig_arm64-armv8a-linuxapp-gcc will be
> > > > > > > used
> > > > > > > by distro folks then that configuration should support
> > > > > > > all the
> > > > > > > devices with
> > > > > > > armv8.1 spec. For instance, marvells new chips are
> > > > > > > armv8.2 but
> > > > > > > we can not make that as default.
> > > > > > What will happen in the future when we will have v9, v10
> > > > > > etc? I
> > > > > > think the distro(generic/binary portable) config should get
> > > > > > rid
> > > > > > of v8.
> > > > > 
> > > > > Will it be too much overhead if the image is same for v8, v9
> > > > > and
> > > > > v10.
> > > > > I think, we can inline with what distro folks are doing for
> > > > > other
> > > > > packages, I think, DPDK package does not need any exception.
> > > > Yes, we need to be inline with any other package. My
> > > > understanding
> > > > is that the image will be same for v8,v9,v10 (any input from
> > > > distro
> > > > engineers will help here). So, my question is, should the
> > > > config
> > > > file/name used by distros contain anything specific to armv8?
> > > Jerin, after following [1], I am not unable to understand when
> > > the
> > > file config/arm/arm64_armv8_linuxapp_gcc gets used. Is this file
> > > required?
> > 
> > If I understand it correctly, only for cross compiling on x86.
> > distro folks build the generic image on arm64 with
> > -Dmachine=default for
> > arm64.
> I thought for cross compilation we have target specific config files
> in config/arm. For ex: arm64_dpaa2_linuxapp_gcc,
> arm64_thunderx_linuxapp_gcc

Yes. config/arm/arm64_armv8_linuxapp_gcc will be used for cross compile
arm64 image, equivalent to config/defconfig_arm64-armv8a-linuxapp-gcc
in cross compiling domain for meson.

> 
> > 
> > > 1. http://mails.dpdk.org/archives/dev/2019-January/123272.html