[Bug 198511] lags in youtube videos 1080p 60fps with radeon hd4650 and kernel 4.15rc8

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https://bugzilla.kernel.org/show_bug.cgi?id=198511

--- Comment #28 from Barto (mister.freeman at laposte.net) ---
I made another test, by using a player like VLC and a video file ( 1080p, 60
FPS ) :

- with a video file 1080p at 60 fps, GPU acceleration disabled ( XV output ) and
kernel 4.15rc8 : I can notice a slight degradation, but less visible than
firefox, it needs a trained eye in order to notice the performance issue,

- with a video file 1080p at 60 fps, GPU acceleration enabled ( VDPAU ) and kernel
4.15rc8 : all is ok, perfect 60 FPS frame, 100% smooth playback

- with a video file 1080p at 60 fps, GPU acceleration disabled ( XV output ) and
kernel 4.14.14: all is ok

the key here is the video resolution and framerate, things get difficult for my
CPU when we reach the resolution 1080p AND the framerate 60 fps, any weak/non
optimized algorithm in kernel ( or video driver ) will likely trigger slight
lags/frame drops,

if I use the "cheat mode" ( GPU acceleration with VDPAU ) then all is ok, no
lags when the video has a resolution 1080p/60 fps and when I use kernel
4.15rc8.

It would be interesting to create a benchmark ( a simple source code in C ) in
order to evaluate with precision ( with a number ) the performance level of
your algorithm related to drm/ttm, it will make easy the comparison between
kernel 4.14.14 ( old algorithm ) and kernel 4.15rc8

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