Re: [RFC PATCH] build: reduce use of AVX compiler flags

[Stephen Hemminger <stephen@networkplumber.org>]

On Wed, 26 Mar 2025 19:06:58 +0100
Morten Brørup <mb@smartsharesystems.com> wrote:

> > From: Bruce Richardson [mailto:bruce.richardson@intel.com]
> > Sent: Wednesday, 26 March 2025 17.22
> > 
> > On Tue, Mar 25, 2025 at 05:22:15PM +0000, Bruce Richardson wrote:  
> > > When doing a build for a target that already has the instruction sets
> > > for AVX2/AVX512 enabled, skip emitting the AVX compiler flags, or the
> > > skylake-avx512 '-march' flags, as they are unnecessary. Instead, when
> > > the default flags produce the desired output, just use them  
> > unmodified.  
> > >
> > > Depends-on: series-34915 ("remove component-specific logic for AVX  
> > builds")  
> > >
> > > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > > ---
> > >
> > > This patchset depends on the previous AVX rework. However, sending it
> > > separately as a new RFC because it effectively increases the minimum
> > > compiler versions needed for x86 builds - from GCC 5 to 6, and
> > > Clang 3.6 to 3.9.
> > >
> > > For now, I've just documented that as an additional note in the GSG  
> > that  
> > > these versions are recommended, but it would be simpler if we could  
> > just  
> > > set them as the required minimum baseline (at least in the docs).
> > >
> > > Feedback on these compiler version requirements welcome.
> > >  
> > 
> > +techboard
> > 
> > Ping for a little bit of feedback for this. Are we ok to bump the
> > minimum
> > compiler versions as described above, or will I continue with the
> > approach
> > in this RFC of keeping the minimum and just recommending the higher
> > versions for x86 platforms?
> > 
> > For reference GCC 6.1 was released April 2016[1], and, Clang 3.9 was
> > released Sept 2016[2]
> > 
> > /Bruce
> > 
> > [1] https://gcc.gnu.org/gcc-6/
> > [2] https://releases.llvm.org/  
> 
> Considering GCC versions shipped with RHEL [3]...
> We kind of support RHEL 7, but we already require a newer compiler (GCC 5) than shipped with RHEL 7 (GCC 4.8).
> RHEL 8 ships with GCC 8, which was released in May 2018 [4]. Maybe we can jump to GCC 8?
> 
> BTW, we should also apply the same principle I argued [5] should apply for upgrading the Kernel requirements: There should be a need for specific feature or similar - which there is with your patch - and the details should be mentioned in the release notes.
> 
> [3]: https://access.redhat.com/solutions/19458
> [4]: https://gcc.gnu.org/gcc-8/
> [5]: https://inbox.dpdk.org/dev/CAMEVEZutf4sJ=EQFONw_bJW0tGTWqTbF_Tk_y38qzBLccco46Q@mail.gmail.com/T/#me7c8f1dbe4331ccf232d43512d6ddb51458c568a
> 

RHEL 7 reached end of life on June 30, 2024.
DPDK need no longer support it on future versions.