Hello Thomas, On 3/3/22 21:58, Thomas Zimmermann wrote: > Rework the fbdev deferred-I/O to not interfere with fields of struct > page. Make the code more flexible and implement GEM SHMEM mmap on top > of it. > > This patchset removes the need for a special shadow framebuffer for > fbdev mmap when using GEM SHMEM. SHMEM pages are now mmap'ed from > /dev/fb directly. > Interesting. I wonder if you have any performance improvements after dropping the shadow buffer. > Patches 2 and 3 rework the fbdev deferred I/O code. It now allows > drivers to have better control of the mmap operations. All references > to fields in struct page are gone. The rsp state is help in a > separate pageref structure. > That's a very nice cleanup. This really was a huge layering violation. > Patches 4 to 7 provide callbacks an helpers to implement deferred I/O > with DRM drivers. Specifically, patch 6 introduces a callback to create > a dumb buffer for fbdev. This will be useful for many drivers that > currently cannot use generic fbdev emulation because of special placement > needs of the BO, such as amdgpu or radeon. The drivers can handle the > differences to regular dumb buffers in their new callback implementation. > > Patch 8 extends the GEM SHMEM memory manager with a new helper for fbdev > dumb-buffer creation. The returned BO has it's mmap set up to implement > deferred I/O with SHMEM pages. No additional shadow buffer is requires > any longer. Many drivers can immediatelly benefit from this change. > > Patch 9 extends virtgpu to support fbdev dumb buffers. It's build on > top of GEM SHMEM, but has some modifications that need to be implemented > for fbdev as well. > > There's no immediate fbdev performance improvement from this patchset. > Most of all, it removes unnecessary shadow framebuffers and rsp memcpys. > A shadow fb for a FullHD display is ~8 MiB, which we now save. The patches > do reduce latency between drawing to the fbdev buffer to displaying > on the screen. Watching a video on the fbdev console felt smoother and > had less flickering. > Awesome. And you also answered here the question I had above. -- Best regards, Javier Martinez Canillas Linux Engineering Red Hat
