Hi Javier

Am 08.03.22 um 10:13 schrieb Javier Martinez Canillas:

Hello Thomas,

On 3/3/22 21:58, Thomas Zimmermann wrote:

quoted

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.

quoted

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.
  

quoted

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.

There's no significant improvement in performance.

But when I play Bug Buck Bunny in mplayer's benchmark mode, the 
displayed animation looks smoother than before. The test finishes in 73 
seconds instead of 74. I guess that one-second improvement comes from 
the memcpy that we now save. I use a somewhat recent Core i7 for 
testing. On old hardware, we might get more performance out of it. I can 
really only guess here.

Best regards
Thomas

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev