Ok, i think I've found culprint to the problem, it's acceleration method, not
DRI3 actually, so maybe i should change the title of the bug report?

Now, with DRI3 and Option "AccelMethod" "EXA", it's actually even better
compared to DRI2 (one tearline, instead of two on DRI2), the problem is glamor
actually (or something connected to it), since it is default on DRI3.

I assume it will act the same on nouveau driver (didn't tried yet), and I think
it's worth investigating further.