I've attached the manuals for the two displays. The relevant pages seem to be:
Samsung Manual: p44 (labeled 42), discusses HDMI in CEA mode for 1080p Acer Manual: p12, standard timing table My best guess for what is happening is that Ubuntu's display output timing over HDMI is slightly out of sync with what the Acer monitor expects, and hence some kind of "re-sync" process is happening about once a second. Or the timing of the laptop's built-in display is slightly different than that of the external monitor, causing the noveau driver to freak out about once a second as it tries to reconcile this. In my Xorg log file, I see a lot of stuff like this: [ 1878.231] (II) intel(0): EDID vendor "LGD", prod id 489 [ 1878.231] (II) intel(0): Printing DDC gathered Modelines: [ 1878.231] (II) intel(0): Modeline "1920x1080"x0.0 138.50 1920 1968 2000 2080 1080 1083 1088 1111 -hsync -vsync (66.6 kHz eP) [ 1879.796] (II) intel(0): Allocated new frame buffer 3840x1080 stride 15360, tiled [ 2099.091] (II) intel(0): EDID vendor "LGD", prod id 489 [ 2099.091] (II) intel(0): Printing DDC gathered Modelines: [ 2099.091] (II) intel(0): Modeline "1920x1080"x0.0 138.50 1920 1968 2000 2080 1080 1083 1088 1111 -hsync -vsync (66.6 kHz eP) [ 2111.153] (II) intel(0): EDID vendor "LGD", prod id 489 [ 2111.153] (II) intel(0): Printing DDC gathered Modelines: [ 2111.154] (II) intel(0): Modeline "1920x1080"x0.0 138.50 1920 1968 2000 2080 1080 1083 1088 1111 -hsync -vsync (66.6 kHz eP) [ 2124.123] (II) intel(0): EDID vendor "LGD", prod id 489 [ 2124.123] (II) intel(0): Printing DDC gathered Modelines: But if I look at the monitor's own menu, I see that the reported refresh rates are H:68KHz, V:60Hz The differences here seem like a likely culprit to me. ** Attachment added: "display_manuals.zip" https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/964231/+attachment/3564050/+files/display_manuals.zip -- You received this bug notification because you are a member of Ubuntu-X, which is subscribed to xserver-xorg-video-intel in Ubuntu. https://bugs.launchpad.net/bugs/964231 Title: System Stutter When HDMI Monitor Is Connected To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/964231/+subscriptions _______________________________________________ Mailing list: https://launchpad.net/~ubuntu-x-swat Post to : ubuntu-x-swat@lists.launchpad.net Unsubscribe : https://launchpad.net/~ubuntu-x-swat More help : https://help.launchpad.net/ListHelp
