[Mesa-dev] Remove classic drivers or fork src/mesa for gallium?

Sun Mar 29 08:19:03 UTC 2020

If you want a complete fork or removal, that's fine with me. It's
technically more challenging for driver loaders and packaging though.

Marek

On Sun., Mar. 29, 2020, 02:51 Jason Ekstrand, <jason at jlekstrand.net> wrote:

> On Sat, Mar 28, 2020 at 11:41 PM Marek Olšák <maraeo at gmail.com> wrote:
> >
> > The #include spaghetti will be resolved before the split. I don't care
> about including gallium, but no code will include src/mesa outside of that.
>
> If we make sure that we modify the #include guards on every header in
> src/mesa_classic so that any accidental cross-includes lead to double
> definitions and therefore compile errors, that would probably help.
> It'd certainly give me a lot more confidence that we've done it right.
>
> > The biggest part is to make src/compiler completely independent and
> that's a worthy goal by itself.
>
> Yeah, I've wanted to see that happen since we started splitting stuff
> out to make Vulkan a possibility.
>
> > Milestones:
> > - make src/compiler a standalone lib
> > - don't include src/mesa in other places
> > - split classic drivers into src/mesa_classic
>
> If you're willing to do the work, I guess I'm not opposed for now.
>
> That said, I also have some somewhat selfish reasons for wanting to do
> a fork.  In particular, I'd like to freeze i965 and possibly Gen7
> Vulkan in time so that we can stop maintaining the i965 and the old
> vec4 back-end compiler.  Even though we're not adding features, I
> still find myself having to fix those up from time to time due to
> reworks elsewhere.  Maybe the answer is to copy and isolate them too
> but, at that point, why not just put them in a branch?
>
> --Jason
>
>
> > Marek
> >
> > On Sun., Mar. 29, 2020, 00:08 Jason Ekstrand, <jason at jlekstrand.net>
> wrote:
> >>
> >> On Wed, Mar 25, 2020 at 6:32 PM Marek Olšák <maraeo at gmail.com> wrote:
> >> >
> >> >
> >> >
> >> > On Thu, Dec 5, 2019 at 2:58 AM Kenneth Graunke <kenneth at whitecape.org>
> wrote:
> >> >>
> >> >> On Tuesday, December 3, 2019 4:39:15 PM PST Marek Olšák wrote:
> >> >> > Hi,
> >> >> >
> >> >> > Here are 2 proposals to simplify and better optimize the
> GL->Gallium
> >> >> > translation.
> >> >> >
> >> >> > 1) Move classic drivers to a fork of Mesa, and remove them from
> master.
> >> >> > Classic drivers won't share any code with master. glvnd will load
> them, but
> >> >> > glvnd is not ready for this yet.
> >> >> >
> >> >> > 2) Keep classic drivers. Fork src/mesa for Gallium. I think only
> mesa/main,
> >> >> > mesa/vbo, mesa/program, and drivers/dri/common need to be forked
> and
> >> >> > mesa/state_tracker moved. src/gallium/state-trackers/gl/ can be
> the target
> >> >> > location.
> >> >> >
> >> >> > Option 2 is more acceptable to people who want to keep classic
> drivers in
> >> >> > the tree and it can be done right now.
> >> >> >
> >> >> > Opinions?
> >> >> >
> >> >> > Thanks,
> >> >> > Marek
> >> >>
> >> >> FWIW, I am not in favor of either plan for the time being.
> >> >>
> >> >> - I agree with Eric that we're finally starting to clean up and
> >> >>   de-duplicate things, and pay off technical debt we've put off for
> >> >>   a long time.  I think forking everything in-tree would just be a
> >> >>   giant mess.
> >> >>
> >> >> - I agree with Dave that this seems to be a giant hassle for our
> >> >>   downstreams with little benefit for them in the short term.
> >> >
> >> >
> >> > If classic drivers were moved to src/mesa_classic, nothing would
> change for downstream.
> >>
> >> I'm concerned that doing that is just asking for more maintenance
> >> problems than we have today.  One of the problems we currently have is
> >> that our #includes are still spaghetti.  We've got stuff in src/util
> >> which inclues stuff in gallium as well as stuff in mesa/main.  If we
> >> even have one cross-wired include, it could lead to bezar and nearly
> >> impossible to trace bugs due to ABI incompatibility between the two
> >> copies of src/mesa the moment we start changing structs or function
> >> prototypes.  The obvious answer to this is "we'll sort out the
> >> spaghetti mess".  However, that also means serious changes to
> >> src/compiler/glsl because it includes mtypes.h.  Do we clone that too?
> >>  I honestly think that this particular cure is likely far worse than
> >> the disease of having to do careful testing of src/mesa changes.
> >>
> >> IMO, a far better plan would be to give it one more year so that
> >> distros and users get experience with iris and then fork off an LTS
> >> branch and delete all the legacy stuff from master.  We can continue
> >> to do maintenance in the LTS branch as needed but I honestly don't
> >> expect much work to happen there.  The most difficult thing will be
> >> deciding what to remove from master but I don't want to make that
> >> decision today.  However, doing a clean fork means we don't have to
> >> worry about cross-contamination in shared code causing weird issues
> >> because they're in separate branches.  We will have to figure out a
> >> few loader issues to ensure that the master drivers get preferred over
> >> the LTS ones or somehow disable all master drivers in the LTS branch.
> >>
> >> --Jason
>
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