Hello,

I have an issue though i'm not really sure where it belongs to, i915,
mesa, drm or xorg, so i'm really sorry if it doesn't belong here.

The issue is as follows:

I em experiencing a very noticeable stuttering (mainly on scroll) in any
app *only* when an external monitor is enabled, and the stutter happens
*only* on the external monitor (normally, see below), connected through
HDMI.

This happens with mirrored or extended xrandr displays.

Is almost as if the external monitor is running on a lower FPS then the
laptop monitor, which is smooth.

If i turn OFF eDP1 display then HDMI display becomes buttery smooth (i
have a very keen eye for FPS, tearing and refresh from playing FPS
games).

Both monitors support and are set to 60hz.

I mainly use awesomewm, compton and and xf86-video-intel ddx (with
TearFree disabled), but i tested the issue in MANY other scenarios, as
described below.

My setup is as follows:
Haswell i7-4700MQ
Clevo W230ST laptop, with nvidia optimus.
Nvidia card is switched off with bbswitch.

Arch Linux
Kernel 4.14.3-1-ARCH #1 SMP PREEMPT
x86_64
Xorg 1.19.5
Mesa 17.2.6



What i've tried without any success:
- Disabling compton
- Using other window manager (openbox)
- Enabling TearFree
- Using xf86 modesetting driver
- i915 kernel flags: enable_psr 1/0, enable_fbc 1/0, edp_swing 2,
enable_dc 1/0, lvds_use_ssc 0, lvds_channel_mode 2


Then i tried using nvidia card (with xrandr --setprovideroutputsource
modesetting NVIDIA-0), which i use for playing, and then the situation
REVERSED (!!!): HDMI is buttery smooth but eDP1 is stuttering, if i
disable either display the problem goes away.


Please help, and thank you very much in advance,
Renato




i915 params:
alpha_support       = "Y"
disable_display     = "N"
disable_power_well  = "1"
edp_vswing          = "0"
enable_cmd_parser   = "Y"
enable_dc           = "-1"
enable_dp_mst       = "Y"
enable_dpcd_backlight= "N"
enable_execlists    = "0"
enable_fbc          = "1"
enable_guc_loading  = "0"
enable_guc_submission= "0"
enable_gvt          = "N"
enable_hangcheck    = "Y"
enable_ips          = "1"
enable_ppgtt        = "1"
enable_psr          = "1"
enable_rc6          = "1"
error_capture       = "Y"
fastboot            = "N"
force_reset_modeset_test= "N"
guc_firmware_path   = "(null)"
guc_log_level       = "-1"
huc_firmware_path   = "(null)"
inject_load_failure = "0"
invert_brightness   = "0"
load_detect_test    = "N"
lvds_channel_mode   = "0"
lvds_use_ssc        = "-1"
mmio_debug          = "0"
modeset             = "-1"
nuclear_pageflip    = "N"
panel_ignore_lid    = "1"
prefault_disable    = "N"
reset               = "2"
semaphores          = "1"
use_mmio_flip       = "0"
vbt_firmware        = "(null)"
vbt_sdvo_panel_type = "-1"
verbose_state_checks= "Y"