On 09.08.2016 17:21, Marek Olšák wrote:
On Tue, Aug 9, 2016 at 3:47 PM, Nicolai Hähnle <nhaeh...@gmail.com> wrote:
Hi everybody,
addrlib is the addressing and alignment calculator which is used by
radeonsi. It's developed (and also used) internally at AMD, and so far we've
had one open source copy living in the Mesa repository at
src/gallium/winsys/amdgpu/drm/addrlib.
The question of using addrlib in non-Mesa parts of our open-source stack has
come up, in particular in relation to compute. We'd obviously like to share
the code rather than having multiple copies flying around. Since the
interface of addrlib is slow-moving but unstable, shared linking is not an
option.
I think the best way forward is to create a dedicated repository for addrlib
which is then integrated into Mesa as a git submodule.
The point of this email is to gather feedback from the Mesa community on
this plan, which is explicitly:
(0) Create an addrlib repository, say amd/addrlib on fd.o.
(1) Add it as a git submodule to the Mesa repository.
(2) Fix up whatever aspects of the build system that may be affected
(perhaps for building source tarballs).
(3) Go back to mostly ignoring addrlib, except for trying to get better at
syncing with the internal closed-source version.
From initial experiments, the impact on users interested in radeon is that
they will have to run `git submodule init` and then occasionally `git
submodule update`. Users who do not build radeonsi should be able to ignore
the change completely.
There are alternatives. For example, ROCm uses Google's repo tool already.
But for Mesa, git submodule looks like a lightweight, well supported and
overall conservative option that everybody should already have installed. If
there are good arguments for something else, let's hear them!
Another point: if we proceed with this plan, I think we should consider
moving addrlib into src/amd/addrlib. There are two reasons: First,
transitioning to a submodule *without* changing the directory is probably
more fragile, i.e. what happens when you switch between checkouts before and
after the transition. Second, if/when radv ends up being merged into Mesa
master, it makes sense to have addrlib there anyway.
Thoughts? Complaints? Praise?
I don't know.
How does this ensure that Mesa and ROCm addrlib copies won't diverge?
They won't really be different copies, because both "copies" are really
checkouts from the same repository. They will occasionally be checkouts
of _different versions_ from the same repository -- usually that would
happen after a sync with the internal copy, when one driver updates
their pointer before the other does. But that's easiy to reconcile.
Usually it should just mean changing the version pointer in whichever
driver uses the older version.
What issues can we expect if Mesa and ROCm addrlib copies diverge?
This is about software maintenance. If we _do_ have separate copies, and
someone applies a bug fix in one copy, they may forget to apply it to
the other. When we want to sync with the internal copy, that has to be
done twice. Basically, all the usual frictions that go with having the
same (or almost the same) piece of code in more than one place.
For texture sharing, the buffer metadata is set in a way that doesn't
leave any room for interpretation. I think it's possible to bypass
addrlib in this case.
Right, this is orthogonal to interoperability. Multiple drivers with
different versions of addrlib can coexist in a system.
Nicolai
Marek
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