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I've configured kdm (editing /usr/share/config/kdm/kdmrc) to automatically open two displays: StaticServers=:0,:1. When I switch between them with Ctrl+Alt+F7-8 there is a delay of about 2 seconds which is extremely annoying.

The same happens when I startx directly from a tty without the intervention of kdm. If I change Window Manager (like openbox or twm) the problem remains.

How could I make this switch as instantaneous as possible?

$ lsmod | grep kms
drm_kms_helper         49262  1 i915
drm                   258005  12 i915,drm_kms_helper
i2c_core               50152  5 drm,i915,i2c_i801,drm_kms_helper,i2c_algo_bit
$ uname -a
Linux hostname 3.16.4-1-ARCH #1 SMP PREEMPT Mon Oct 6 08:22:27 CEST 2014 x86_64 GNU/Linux
$ lspci |grep -e VGA -e 3D
00:02.0 VGA compatible controller: Intel Corporation Xeon E3-1200 v2/3rd Gen Core processor Graphics Controller (rev 09)
$ grep -e driver /var/log/Xorg.0.log 
[     4.624]    X.Org XInput driver : 21.0
[     4.627] (==) Matched intel as autoconfigured driver 0
[     4.627] (==) Matched modesetting as autoconfigured driver 1
[     4.627] (==) Matched fbdev as autoconfigured driver 2
[     4.627] (==) Matched vesa as autoconfigured driver 3
[     4.627] (==) Assigned the driver to the xf86ConfigLayout
[     4.627] (II) Loading /usr/lib/xorg/modules/drivers/intel_drv.so
[     4.962] (II) intel(0): Using Kernel Mode Setting driver: i915, version 1.6.0 20080730
[     4.964] (II) intel(0): [DRI2]   DRI driver: i965
[     4.964] (II) intel(0): [DRI2]   VDPAU driver: i965
[     5.032]    ABI class: X.Org XInput driver, version 21.0
[     5.032] (II) Using input driver 'evdev' for 'Power Button'
[     5.053] (II) Using input driver 'evdev' for 'Video Bus'
[     5.053] (II) Using input driver 'evdev' for 'Power Button'
[     5.054] (II) Using input driver 'evdev' for 'Forward USB Optical Mouse'
[     5.055] (II) No input driver specified, ignoring this device.
[     5.055] (II) Using input driver 'evdev' for 'Microsoft Comfort Mouse 6000'
[     5.056] (II) No input driver specified, ignoring this device.
[     5.056] (II) Using input driver 'evdev' for 'Microsoft Natural® Ergonomic Keyboard 4000'
[     5.057] (II) Using input driver 'evdev' for 'Microsoft Natural® Ergonomic Keyboard 4000'
[     5.057] (II) No input driver specified, ignoring this device.
$ dmesg | grep drm
[    2.696528] [drm] Initialized drm 1.1.0 20060810
[    2.793949] [drm] Memory usable by graphics device = 2048M
2.793951] [drm] Replacing VGA console driver
2.793955] fb: switching to inteldrmfb from VESA VGA
2.813970] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
2.813971] [drm] Driver supports precise vblank timestamp query.
[    2.890589] [drm] GMBUS [i915 gmbus dpc] timed out, falling back to bit banging on pin 4
[    2.991700] fbcon: inteldrmfb (fb0) is primary device
[    3.027016] [drm:cpt_set_fifo_underrun_reporting] *ERROR* uncleared pch fifo underrun on pch transcoder A
[    3.027017] [drm:cpt_serr_int_handler] *ERROR* PCH transcoder A FIFO underrun
[    3.033464] i915 0000:00:02.0: fb0: inteldrmfb frame buffer device
[    3.062197] [drm] Initialized i915 1.6.0 20080730 for 0000:00:02.0 on minor 0
[    4.314306] [drm] Enabling RC6 states: RC6 on, RC6p on, RC6pp off
  • 1
    What display driver are you using? This will likely go away if you use a driver that uses KMS. – Patrick Oct 8 '14 at 2:00
  • Thanks.... I updated my question with the output of Xorg.log,... I think it does use KMS, right? – Konstantinos Oct 8 '14 at 3:51
  • I think it's a KMS issue but cannot activate it. It seems activated (following wiki.archlinux.org/index.php/Kernel_Mode_Setting did not help), but user-switching takes time a couple or more of seconds. It certainly isn't hardware related, because it works in ubuntu, but not in Arch :( – Konstantinos Oct 8 '14 at 23:02

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