Wrong v-sync framerate with multiple monitors having different refresh rates


my setup currently consists of a 144Hz G-sync monitor connected via DisplayPort and an older 60Hz one connected via HDMI. Both are set via the driver to their respective native framerate, and their OSD’s show the correct values. However, when I start glxgears with v-sync enabled on the first (144Hz) monitor, it still renders with only 60fps. This is as long as the second monitor is switched on; disabling it via

xrandr --output HDMI-0 --off

boosts glxgears’ v-synced framerate to 144fps. Re-enabling the 60Hz monitor again will make glxgears drop down to 60fps again. This behaviour can be observed even with glxgears running during the off/on switches.

Different X screens for both monitors didn’t make any difference either. The only means to get 144Hz right now therefore is disabling the second monitor, which would naturally remove the benefit of having two monitors. Needless to say that G-sync does not work with both monitors on, but does with only one (the G-sync one, of course).

What might be of interest here, selecting “auto” mode in the nvidia-settings panel for the 144Hz monitor results in the driver selecting 60Hz. xrandr --prop also shows 60Hz as the preferred mode of the monitor.

The nvidia-bug-report.log.gz file can be found here.

The monitors are an Acer Predator XB270H (G-sync variant) and a Samsung SyncMaster P2450, graphics card GTX 970. Window manager is Enlightenment; the framerate in its performance settings is set to 144, however this doesn’t appear to affect the actual output but rather the compositor’s rendering only.
G-sync and 144Hz are working on the same machine under Windows (at least for fullscreen applications/games), however i cannot confirm the framerate in windowed mode.

Any help with fixing this would be greatly appreciated, as the mismatching framerate on the first monitor does cause a (sometimes heavily) visible stuttering.