Helping Wine use 64 bit Mesa OGL drivers for 32-bit Windows applications

Mon Oct 21 21:21:29 UTC 2024

On 10/21/24 07:33, Jose Fonseca wrote:
> I see a few downsides with the proposed callback:
> - feels like a solution too tailored for WINE
> - there's a layering violation: the application suddenly takes the 
> driving seat for a thing deep down in the GL driver
> so I fear Mesa community might regret it doing, and once WINE supports 
> there would be outcry if to go back.
> 
> 
> IIUC the problem at hand, another way to go about this would be an 
> extension that allows applications to get a malloc'ed/valloc'ed memory 
> exposed to the GPU as a GL buffer object.
> 
> I feel this would be potentially useful to applications other than just 
> WINE, especially on systems with unified memory.  And there have been 
> extensions along these lines before, for example, 
> https://registry.khronos.org/OpenGL/extensions/AMD/AMD_pinned_memory.txt 
> <https://registry.khronos.org/OpenGL/extensions/AMD/AMD_pinned_memory.txt>

These ideas by themselves make it very difficult to get e.g., a mapping 
of a device memory region as opposed to a system memory buffer, and...

> There's also NVIDIA's Heterogeneous Memory Management, which takes this 
> idea to a whole different level:
> - 
> https://developer.nvidia.com/blog/simplifying-gpu-application-development-with-heterogeneous-memory-management/ <https://developer.nvidia.com/blog/simplifying-gpu-application-development-with-heterogeneous-memory-management/>
> - https://www.kernel.org/doc/html/v5.0/vm/hmm.html 
> <https://www.kernel.org/doc/html/v5.0/vm/hmm.html>
> - 
> https://lpc.events/event/2/contributions/70/attachments/14/6/hmm-lpc18.pdf <https://lpc.events/event/2/contributions/70/attachments/14/6/hmm-lpc18.pdf>
> - https://lwn.net/Articles/752964/ <https://lwn.net/Articles/752964/>
> - https://lwn.net/Articles/684916/ <https://lwn.net/Articles/684916/>

These are great, but seem like overkill for this problem space.

The Vulkan solution was very minimally invasive from a driver point of 
view. If only WINE ends up using it, it's not that big of a deal. WINE 
is a common use case, and there are plenty of things in graphics APIs 
that cater to one or a small set of very impactful use cases. If the 
OpenGL extension had a similarly small footprint, it also wouldn't be 
that big of a deal if it were tailored to WINE. Note Vulkan already has 
the equivalent of the above AMD extension, and chose to add additional 
functionality for this particular use case anyway.

All that said, I don't love the idea of callbacks either. Callbacks in 
general are tough to specify and use robustly, and hence should be a 
last resort. E.g., this particular callback might sometimes come from 
the application thread, and sometimes come from some separate 
driver-managed thread. It's hard to validate that all applications can 
handle that properly and wouldn't do something crazy like rely on their 
own TLS data in the callback or try to call back into OpenGL from the 
callback and deadlock themselves, even if these are clearly specified as 
an unsupported actions.

Thanks,
-James

> But I remember that Thomas Hellstrom (while at VMware, now Intel) once 
> prototyped this without HMM, just plain DRM.  I think HMM provides the 
> ability to do this transparently for application, which is above and 
> beyond what's strictly needed for WINE.
> 
> Metal API also provides this -- 
> https://developer.apple.com/documentation/metal/mtldevice/1433382-newbufferwithbytesnocopy?language=objc <https://developer.apple.com/documentation/metal/mtldevice/1433382-newbufferwithbytesnocopy?language=objc>
> 
> Jose
> 
> On Fri, Oct 18, 2024 at 11:10 PM Derek Lesho <dlesho at codeweavers.com 
> <mailto:dlesho at codeweavers.com>> wrote:
> 
>     Hey everyone 👋,
> 
>     I'm Derek from the Wine project, and wanted to start a discussion with
>     y'all about potentially extending the Mesa OGL drivers to help us
>     with a
>     functionality gap we're facing.
> 
>     Problem Space:
> 
>     In the last few years Wine's support for running 32-bit windows apps in
>     a 64-bit host environment (wow64) has almost reached feature
>     completion,
>     but there remains a pain point with OpenGL applications: Namely that
>     Wine can't return a 64-bit GL implementation's buffer mappings to a 32
>     bit application when the address is outside of the 32-bit range.
> 
>     Currently, we have a workaround that will copy any changes to the
>     mapping back to the host upon glBufferUnmap, but this of course is slow
>     when the implementation directly returns mapped memory, and doesn't
>     work
>     for GL_PERSISTENT_BIT, where directly mapped memory is required.
> 
>     A few years ago we also faced this problem with Vulkan's, which was
>     solved through the VK_EXT_map_memory_placed extension Faith drafted,
>     allowing us to use our Wine-internal allocator to provide the pages the
>     driver maps to. I'm now wondering if an GL equivalent would also be
>     seen
>     as feasible amongst the devs here.
> 
>     Proposed solution:
> 
>     As the GL backend handles host mapping in its own code, only giving
>     suballocations from its mappings back to the App, the problem is a
>     little bit less straight forward in comparison to our Vulkan solution:
>     If we just allowed the application to set its own placed mapping when
>     calling glMapBuffer, the driver might then have to handle moving
>     buffers
>     out of already mapped ranges, and would lose control over its own
>     memory
>     management schemes.
> 
>     Therefore, I propose a GL extension that allows the GL client to
>     provide
>     a mapping and unmapping callback to the implementation, to be used
>     whenever the driver needs to perform such operations. This way the
>     driver remains in full control of its memory management affairs, and
>     the
>     amount of work for an implementation as well as potential for bugs is
>     kept minimal. I've written a draft implementation in Zink using
>     map_memory_placed [1] and a corresponding Wine MR utilizing it [2], and
>     would be curious to hear your thoughts. I don't have experience in the
>     Mesa codebase, so I apologize if the branch is a tad messy.
> 
>     In theory, the only requirement from drivers from the extension
>     would be
>     that glMapBuffer always return a pointer from within a page allocated
>     through the provided callbacks, so that it can be guaranteed to be
>     positioned within the required address space. Wine would then use it's
>     existing workaround for other types of buffers, but as Mesa seems to
>     often return directly mapped buffers in other cases as well, Wine could
>     also avoid the slowdown that comes with copying in these cases as well.
> 
>     Why not use Zink?:
> 
>     There's also a proposal to use a 32-bit PE build of Zink in Wine
>     bypassing the need for an extension; I brought this to discussion in
>     this Wine-Devel thread last week [3], which has some arguments against
>     this approach.
> 
> 
>     If any of you have thoughts, concerns, or questions about this
>     potential
>     approach, please let me know, thanks!
> 
>     1:
>     https://gitlab.freedesktop.org/Guy1524/mesa/-/commits/placed_allocation <https://gitlab.freedesktop.org/Guy1524/mesa/-/commits/placed_allocation>
> 
>     2: https://gitlab.winehq.org/wine/wine/-/merge_requests/6663
>     <https://gitlab.winehq.org/wine/wine/-/merge_requests/6663>
> 
>     3: https://marc.info/?t=172883260300002&r=1&w=2
>     <https://marc.info/?t=172883260300002&r=1&w=2>
> 
> 
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