[Development] Using DMA instead of SHM in non OpenGL apps (Linux/Wayland)

[Giuseppe D'Angelo]

Hi,

On 25/08/2023 12:34, Vlad Zahorodnii wrote:
>> I'm really curious here, and these aren't rhetorical questions: why
>> would anyone expect to be a difference in performance, as far as
>> QPainter is concerned? Isn't it ultimately just using a CPU-based
>> renderer onto a block of memory? Why should it make a difference where
>> that memory comes from / how it's managed / etc.? Are we're talking
>> about "far memory" (NUMA-like) scenarios?

> It makes a difference to the compositor. The compositor will have to
> upload pixel data from RAM to VRAM so it can composite the windows using
> OpenGL or Vulkan. If the client provides dmabuf client buffers, the
> compositor can skip the uploading step thus reduce the amount of time it
> takes to compose a frame.

Thanks, this part was OK with me. I was confused by the previous emails 
possibly implying that QPainter-based painting *alone* was making a 
difference between DMA and SHM, and couldn't understand why.

-- 
Giuseppe D'Angelo | giuseppe.dangelo at kdab.com | Senior Software Engineer
KDAB (France) S.A.S., a KDAB Group company
Tel. France +33 (0)4 90 84 08 53, http://www.kdab.com
KDAB - The Qt, C++ and OpenGL Experts

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