Mysterious heavy slowdown when playing 1080p videos through VDPAU
I first spotted this issue with 285.x series drivers though I don't play 1080p all that much so it could've been there for a longer time.
Whenever I play a 1080p video accelerated though VDPAU, the playback is very slow, the whole system slows down to a crawl, even the mouse cursor lags in X. It doesn't matter which player I use, I can reproduce this with mplayer, flashplugin, VLC. To resolve the situation I have to open nvidia-settings while the video is playing and set PowerMizer to "maximum performance". Everything gets up to speed almost immediately and I can switch the PowerMizer back to "adaptive" again. The card then clocks down to power level 2 and stays there. When the player is closed and opened again, I have to repeat this procedure.
When VDPAU is not used to accelerate decoding, I don't have this problem. There's also nothing wrong with 720p videos. The problem is still present in 290.06.