[ovs-dev] [PATCH v2 1/1] dpdk: Update to use DPDK v20.11.

[Luca Boccassi]

On Mon, 2020-12-14 at 15:24 +0100, Ilya Maximets wrote:
> On 12/14/20 3:17 PM, Luca Boccassi wrote:
> > On Mon, 2020-12-14 at 15:05 +0100, David Marchand wrote:
> > > On Mon, Dec 14, 2020 at 12:45 PM Ilya Maximets <i.maximets at ovn.org> wrote:
> > > > > On DPDK side, it should only be a couple of headers that are causing compilation
> > > > > issues, and we can investigate what we can do with them - at least some of them
> > > > > can be reworked to support a non-SSE4.2 fallback, I believe. If we can rework
> > > > > them that would then remove the SSE4.2 requirement for any code paths not using DPDK.
> > > > > In parallel we can also see if the -march flag could be just replaced with an -msse
> > > > > one.
> > > > 
> > > > Sounds reasonable.  Removing of the SSE4.2 requirement would be great.
> > > > 
> > > > But we still have an issue with this particular patch for OVS right now that can
> > > > not wait for the next stable DPDK version.
> > > > 
> > > > I'd stick with stripping out '-march=.*' from DPDK_INCLUDE (patch above) and
> > > > conditionally adding '-mssse3' if compiler supports (we already have this and
> > > > had no issues building with DPDK in this configuration starting from DPDK 2.0.
> > > > I also worked with OVS + DPDK on arm and it was never required to pass any
> > > > specific compiler flags to OVS in order to build and work correctly).
> > > > This will be re-considered once DPDK changes accepted.
> > > 
> > > OVS has lived with SSSE3 so far, while the requirement to SSE4.2 was
> > > added back in dpdk 17.08.
> > > Stripping -march for now is the simplest/best approach.
> > 
> > That's because we fixed it on the distro side long ago. This _will_
> > reintroduce regressions. Please don't add more work on us.
> 
> Could you, please, point to these regressions, so we can check them?
> 
> "there are no issues" vs "there are issues" dialog makes no much sense.
> 
> Best regards, Ilya Maximets.

It's future tense - I can't quite post bug reports from the future
unfortunately, my home network is fast but it doesn't yet break
causality :-)

The whole workstream of adding pkg-config in DPDK started in Debian and
Ubuntu from myself and Christian long before upstream supported it,
years earlier in fact. We did that because there are significant and
critical information, decided by DPDK at build time, that needs to flow
down to applications linking against it for everything to work
properly.

Second-guessing this information and unconditionally overriding it will
only produce more work for those of us who have to integrate the whole
thing in a way that works.

So please don't do that. If you want to add _manual_ overrides that
someone who rebuilds locally can choose to use, that's fine by me.

-- 
Kind regards,
Luca Boccassi