[TapamN]

It seems like it should be possible to do the X async method without tearing.

When updating the cursor position, check if line being output overlaps with the cursor. If it isn't, it's safe to update the hardware cursor immediately, without tearing. Otherwise, defer updating the cursor until later (vblank would work) to avoid tearing.

Of course, this assumes it's possible to read what row of the frame buffer is being displayed. I think most hardware would support it, but I could see driver support being poorly tested, or possibly even missing entirely from Linux's video APIs.

[arghwhat]

This would have to be done by the kernel driver for you GPU. I kind of doubt that it's possible (you're not really scanning out lines anymore with things like Display Stream Compression, partial panel self refresh and weird buffer formats), and doubt even more that kernel devs would consider it worth the maintenance burden...

[gf000]

I believe this is called "racing the beam".

But given that different displays work differently, I'm not sure it would worth the hassle.

[bandrami]

I mean at some point it's a fundamental choice though, right? You can either have sync problems or lag problems and there's a threshold past which improving one makes the other worse. (This is true in audio, at least, and while I don't know video that well I can't see why it would be different.)