On 17/02/2022 18:21, Ivaylo Dimitrov wrote:
Hi Tomi,
On 17.02.22 г. 15:03 ч., Tomi Valkeinen wrote:
Hi Ivaylo,
On 19/01/2022 12:23, Ivaylo Dimitrov wrote:
This patch series fixes excessive DMM or CMA usage of GEM buffers
leading to
various runtime allocation failures. The series enables daily usage
of devices
without exausting limited resources like CMA or DMM space if GPU
rendering is
needed.
The first patch doesn't bring any functional changes, it just moves some
TILER/DMM related code to a separate function, to simplify the review
of the
next two patches.
The second patch allows off-CPU rendering to non-scanout buffers.
Without that
patch, it is basically impossible to use the driver allocated GEM
buffers on
OMAP3 for anything else but a basic CPU rendered examples as if we
want GPU
rendering, we must allocate buffers as scanout buffers, which are CMA
allocated.
CMA soon gets fragmented and we start seeing allocation failures.
Such failres
in Xorg cannot be handeled gracefully, so the system is basically
unusable.
Third patch fixes similar issue on OMAP4/5, where DMM/TILER spaces get
fragmented with time, leading to allocation failures.
I think this is just hacking around the problem. The problem is that
omapdrm is being used by some as a generic buffer allocator. Those users
Well, the user of omap_bo interface I know is xf86-video-omap. Unless if
by users you mean 'kernel users' which I know none.
I think that if 'we' are to teach xorg omap DDX (or any other user in
that regard) to use GPU driver allocator for non-scanout buffers and
omapdrm for scanout, it will become a mess. Not impossible though, just
way more complicated than the $series. Also, why do omapdrm allow
allocation of non-linear buffers and CPU (userspace) access to them, but
refuses to export them to kernel drivers? Isn't that the whole point of
DMABUF stuff? This is not consistent to me. The series fixes that
inconsistency, nothing more.
should be changed to use a their own allocator or a generic allocator.
SGX driver/userspace has and uses its own allocator, however, I think
there is more than that - what about TILER/VRFB? Do you say that SGX
userspace shall be smart enough to requests TILER buffers from omapdrm
when scanout buffer is requested and use its own allocator when not?
All I'm saying is that omapdrm should not support allocating buffers
that are not usable by the omapdrm hardware. It doesn't make any sense.
Actually I was thinking about something like that, and it is achievable
now we have:
https://github.com/maemo-leste/sgx-ddk-um/blob/master/dbm/dbm.c (REed
SGX 1.17 ddk gbm backend)
And we could then drop the OMAP_BO_SCANOUT flag, as all buffers would
be scanout buffers.
And what about OMAP_BO_TILED_XX stuff? To me this is even more of a
hack, but it is what it is.
Yes, I agree, I don't think those OMAP_BO_TILED_* values should be
exposed to userspace. But I also agree to the "it is what it is" =).
Do I get it correctly that you want to get rid of omap_bo_new/_tiled and
have only dumb buffers available in omapdrm? TBH this would be great,
however I still don't see how a TILER/VRFB buffer would be allocated,
given that flags in drm_mode_create_dumb is not used anywhere in the
kernel(AFAIK). Unless all scanout buffers are allocated through
TILER/VRFB (which is a good idea IMO).
We can't get rid of those as they're userspace API.
Or do we have a regression in the driver? My understanding is that
this has never really worked.
There are couple of patches in omapdrm that change around BO flags and
their meaning so I think there is a regression, as the same
userspace/DDX on linux 5.9 results in only 2 linear buffers being
allocated, but as SGX driver has different version as well, I can't be
100% sure without going through a lengthy assessment of SGX
driver/omapdrm code and patches since 5.9. Which I am not going to do as
I don't see what the benefit will be.
Please consider this patch series as a fix to an inconsistency, as it is
merely that, it does not really bring any new functionality in terms of
what is allocated.
I've considered, and I think I agree. The design of omapdrm + tiler is
broken in my opinion, but it's there, it has userspace APIs, and it's
all old code. It's probably not worth the effort to try to clean it up,
while still somehow keeping the old userspace working.
I've had these patchesin my work branch for a while and I haven't seen
any issues. I'll keep them there for a bit longer and I'll look at these
patches a bit more, but I think I'll merge them at some point.
Tomi
