Re: [Mesa-dev] [PATCH 0/6] dma-buf: Add an API for exporting sync files (v12)
On Mon, Jun 21, 2021 at 12:16:55PM +0200, Christian König wrote:
> Am 18.06.21 um 20:45 schrieb Daniel Vetter:
> > On Fri, Jun 18, 2021 at 8:02 PM Christian König
> > wrote:
> > > Am 18.06.21 um 19:20 schrieb Daniel Vetter:
> > > [SNIP]
> > > The whole thing was introduced with this commit here:
> > >
> > > commit f2c24b83ae90292d315aa7ac029c6ce7929e01aa
> > > Author: Maarten Lankhorst
> > > Date: Wed Apr 2 17:14:48 2014 +0200
> > >
> > > drm/ttm: flip the switch, and convert to dma_fence
> > >
> > > Signed-off-by: Maarten Lankhorst
> > >
> > >int ttm_bo_move_accel_cleanup(struct ttm_buffer_object *bo,
> > >
> > > - bo->sync_obj = driver->sync_obj_ref(sync_obj);
> > > + reservation_object_add_excl_fence(bo->resv, fence);
> > > if (evict) {
> > >
> > > Maarten replaced the bo->sync_obj reference with the dma_resv exclusive
> > > fence.
> > >
> > > This means that we need to apply the sync_obj semantic to all drivers
> > > using a DMA-buf with its dma_resv object, otherwise you break imports
> > > from TTM drivers.
> > >
> > > Since then and up till now the exclusive fence must be waited on and
> > > never replaced with anything which signals before the old fence.
> > >
> > > Maarten and I think Thomas did that and I was always assuming that you
> > > know about this design decision.
> > Surprisingly I do actually know this.
> >
> > Still the commit you cite did _not_ change any of the rules around
> > dma_buf: Importers have _no_ obligation to obey the exclusive fence,
> > because the buffer is pinned. None of the work that Maarten has done
> > has fundamentally changed this contract in any way.
>
> Well I now agree that the rules around dma_resv are different than I
> thought, but this change should have raised more eyebrows.
>
> The problem is this completely broke interop with all drivers using TTM and
> I think might even explain some bug reports.
>
> I re-introduced the moving fence by adding bo->moving a few years after the
> initial introduction of dma_resv, but that was just to work around
> performance problems introduced by using the exclusive fence for both use
> cases.
Ok that part is indeed not something I've known.
> > If amdgpu (or any other ttm based driver) hands back and sgt without
> > waiting for ttm_bo->moving or the exclusive fence first, then that's a
> > bug we need to fix in these drivers. But if ttm based drivers did get
> > this wrong, then they got this wrong both before and after the switch
> > over to using dma_resv - this bug would go back all the way to Dave's
> > introduction of drm_prime.c and support for that.
>
> I'm not 100% sure, but I think before the switch to the dma_resv object
> drivers just waited for the BOs to become idle and that should have
> prevented this.
>
> Anyway let's stop discussing history and move forward. Sending patches for
> all affected TTM driver with CC: stable tags in a minute.
>
>
> > The only thing which importers have to do is not wreak the DAG nature
> > of the dma_resv fences and drop dependencies. Currently there's a
> > handful of drivers which break this (introduced over the last few
> > years), and I have it somewhere on my todo list to audit them all.
>
> Please give that some priority.
>
> Ignoring the moving fence is a information leak, but messing up the DAG
> gives you access to freed up memory.
Yeah will try to. I've also been hung up a bit on how to fix that, but I
think just closing the DAG-breakage is simplest. Any userspace which then
complains about the additional sync that causes would then be motivated to
look into the import ioctl Jason has. And I think the impact in practice
should be minimal, aside from some corner cases.
> > The goal with extracting dma_resv from ttm was to make implicit sync
> > working and get rid of some terrible stalls on the userspace side.
> > Eventually it was also the goal to make truly dynamic buffer
> > reservation possible, but that took another 6 or so years to realize
> > with your work. And we had to make dynamic dma-buf very much opt-in,
> > because auditing all the users is very hard work and no one
> > volunteered. And for dynamic dma-buf the rule is that the exclusive
> > fence must _never_ be ignored, and the two drivers supporting it (mlx5
> > and amdgpu) obey that.
> >
> > So yeah for ttm drivers dma_resv is primarily for memory management,
> > with a side effect of also supporting implicit sync.
> >
> > For everyone else (and this includes a pile of render drivers, all the
> > atomic kms drivers, v4l and I have no idea what else on top) dma_resv
> > was only ever about implicit sync, and it can be ignored. And it (the
> > implicit sync side) has to be ignored to be able to support vulkan
> > winsys buffers correctly without stalling where we shouldn't. Also we
> > have to ignore it on atomic kms side too (and depending upon whether
> > writeback is supported atomic kms is perfectly capable of reading out
> >
Re: color management release version
On Mon, 21 Jun 2021 17:07:25 +0800 l...@codeaurora.org wrote: > Hi pekka > > I see there are a lot of discussions for color management in > https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/14 > and a lot of details in > https://www.collabora.com/news-and-blog/blog/2020/11/19/developing-wayland-color-management-and-high-dynamic-range/, > > may I ask which version of wayland-protocols and weston will merged > related changes? Thank you! Hi, that is impossible to say. Right now my goal is to get as much code into Weston upstream as possible to facilitate experimenting on the protocol design and tone-mapping, and then get back to protocol design which still has many open questions and to-dos. The wayland-protocols MR cannot land until we have at least three implementations, and all the details have been sorted out and shown to work. So that is pretty much the last thing to merge. I believe it will not be this year. You can also follow https://gitlab.freedesktop.org/wayland/weston/-/issues/467 Thanks, pq pgpkYoXEZsgIg.pgp Description: OpenPGP digital signature ___ wayland-devel mailing list wayland-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/wayland-devel
Re: [Mesa-dev] [PATCH 0/6] dma-buf: Add an API for exporting sync files (v12)
Am 18.06.21 um 20:45 schrieb Daniel Vetter:
On Fri, Jun 18, 2021 at 8:02 PM Christian König
wrote:
Am 18.06.21 um 19:20 schrieb Daniel Vetter:
[SNIP]
The whole thing was introduced with this commit here:
commit f2c24b83ae90292d315aa7ac029c6ce7929e01aa
Author: Maarten Lankhorst
Date: Wed Apr 2 17:14:48 2014 +0200
drm/ttm: flip the switch, and convert to dma_fence
Signed-off-by: Maarten Lankhorst
int ttm_bo_move_accel_cleanup(struct ttm_buffer_object *bo,
- bo->sync_obj = driver->sync_obj_ref(sync_obj);
+ reservation_object_add_excl_fence(bo->resv, fence);
if (evict) {
Maarten replaced the bo->sync_obj reference with the dma_resv exclusive
fence.
This means that we need to apply the sync_obj semantic to all drivers
using a DMA-buf with its dma_resv object, otherwise you break imports
from TTM drivers.
Since then and up till now the exclusive fence must be waited on and
never replaced with anything which signals before the old fence.
Maarten and I think Thomas did that and I was always assuming that you
know about this design decision.
Surprisingly I do actually know this.
Still the commit you cite did _not_ change any of the rules around
dma_buf: Importers have _no_ obligation to obey the exclusive fence,
because the buffer is pinned. None of the work that Maarten has done
has fundamentally changed this contract in any way.
Well I now agree that the rules around dma_resv are different than I
thought, but this change should have raised more eyebrows.
The problem is this completely broke interop with all drivers using TTM
and I think might even explain some bug reports.
I re-introduced the moving fence by adding bo->moving a few years after
the initial introduction of dma_resv, but that was just to work around
performance problems introduced by using the exclusive fence for both
use cases.
If amdgpu (or any other ttm based driver) hands back and sgt without
waiting for ttm_bo->moving or the exclusive fence first, then that's a
bug we need to fix in these drivers. But if ttm based drivers did get
this wrong, then they got this wrong both before and after the switch
over to using dma_resv - this bug would go back all the way to Dave's
introduction of drm_prime.c and support for that.
I'm not 100% sure, but I think before the switch to the dma_resv object
drivers just waited for the BOs to become idle and that should have
prevented this.
Anyway let's stop discussing history and move forward. Sending patches
for all affected TTM driver with CC: stable tags in a minute.
The only thing which importers have to do is not wreak the DAG nature
of the dma_resv fences and drop dependencies. Currently there's a
handful of drivers which break this (introduced over the last few
years), and I have it somewhere on my todo list to audit them all.
Please give that some priority.
Ignoring the moving fence is a information leak, but messing up the DAG
gives you access to freed up memory.
The goal with extracting dma_resv from ttm was to make implicit sync
working and get rid of some terrible stalls on the userspace side.
Eventually it was also the goal to make truly dynamic buffer
reservation possible, but that took another 6 or so years to realize
with your work. And we had to make dynamic dma-buf very much opt-in,
because auditing all the users is very hard work and no one
volunteered. And for dynamic dma-buf the rule is that the exclusive
fence must _never_ be ignored, and the two drivers supporting it (mlx5
and amdgpu) obey that.
So yeah for ttm drivers dma_resv is primarily for memory management,
with a side effect of also supporting implicit sync.
For everyone else (and this includes a pile of render drivers, all the
atomic kms drivers, v4l and I have no idea what else on top) dma_resv
was only ever about implicit sync, and it can be ignored. And it (the
implicit sync side) has to be ignored to be able to support vulkan
winsys buffers correctly without stalling where we shouldn't. Also we
have to ignore it on atomic kms side too (and depending upon whether
writeback is supported atomic kms is perfectly capable of reading out
any buffer passed to it).
Oh! That might actually explain some issues, but that just completely
breaks when TTM based drivers use atomic.
In other words for the first use is actually rather likely for TTM based
drivers to need to move the buffer around so that scanout is possible.
And that in turn means you need to wait for this move to finish even if
you have an explicit fence to wait for. IIRC amdgpu rolled its own
implementation of this and radeon doesn't have atomic, but nouveau is
most like broken.
So we do need a better solution for this sooner or later.
It's absolutely not that this is my invention, I'm just telling you how
it ever was.
Anyway this means we have a seriously misunderstanding and yes now some
of our discussions about dynamic P2P suddenly make much more sense.
Yeah I think
color management release version
Hi pekka I see there are a lot of discussions for color management in https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/14 and a lot of details in https://www.collabora.com/news-and-blog/blog/2020/11/19/developing-wayland-color-management-and-high-dynamic-range/, may I ask which version of wayland-protocols and weston will merged related changes? Thank you! Best Regards Nancy ___ wayland-devel mailing list wayland-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/wayland-devel
