Re: [dpdk-dev] [RFC PATCH] build/pkg-config: remove machine arch flag

[David Christensen <drc@linux.vnet.ibm.com>]

On 12/11/20 7:51 AM, Bruce Richardson wrote:
> Traditionally any apps built using DPDK had to support the same
> instruction sets as supported when the DPDK SDK itself was built, since
> that was "leaked" through to the end-app and DPDK headers via
> RTE_MACHINE_CPUFLAG_* values. Therefore, when converting over to meson
> for app build correctness the "-march=" flag was included in the
> pkg-config cflags output.
> 
> However, since the DPDK-specific CPU flags are now obsolete, and we
> instead check directly for compiler-defined flags, we should no longer
> need to force the exact same architecture match in all cases. To
> faciliate such flexibility, a new pkg_config_machine_args array - which
> defaults to the existing machine_args array has been defined. The
> individual architectures - x86, arm and ppc - can choose if and how to
> override this value themselves.
> 
> For x86, since SSE4.2 is the minimum instruction-set level needed to run
> DPDK, and since some header files assume that minimum level of
> instruction set support, we override the "-march=" value with "-msse4"
> for the pkg-config file. This allows end applications to set their own
> "march" value while still ensuring valid DPDK compilation.
> 
> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> ---
> 
> CC: Jerin Jacob <jerinj@marvell.com>
> CC: Ruifeng Wang <ruifeng.wang@arm.com>
> CC: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> CC: David Christensen <drc@linux.vnet.ibm.com>
> Feedback requested from ARM and PPC maintainers as to this change
> and what flags, if any, need to be in the .pc file for DPDK on such
> platforms. For example - is setting 'pkg_config_machine_args' to
> 'machine_args' by default necessary behaviour?

Support for Altivec would be the equivalent here for PPC and I'm not 
aware of any additional flags required for supported POWER CPUs on DPDK. 
  I can't speak to P10 requirements yet but the proposed change is a 
don't care for me.

Dave