I experience a complete lockup every 1-3 days, except the mouse cursor still moves.  Keyboard LED's don't flash.  Num/Caps/Scroll Lock doesn't toggle the keyboard LED's.  Can't switch to text tty's.  Can't ping its IP or ssh into from another machine.  Proprietary nVidia driver works fine.  This has been happening since I switched to nouveau a few months ago.

JOURNALCTL SHOWS (VIEWABLE AFTER REBOOT)
Sep 12 08:45:39 kvm kernel: nouveau E[   PFIFO][0000:06:00.0] SCHED_ERROR [ CTXSW_TIMEOUT ]
Sep 12 08:45:39 kvm kernel: nouveau E[   PFIFO][0000:06:00.0] PGRAPH engine fault on channel 7, recovering...
Sep 12 09:22:18 kvm kernel: nouveau E[   PFIFO][0000:06:00.0] PBDMA0: ACQUIRE
Sep 12 09:22:18 kvm kernel: nouveau E[   PFIFO][0000:06:00.0] PBDMA0: ch 2 [Xorg[655]] subc 0 mthd 0x001c data 0x00001004
{{{ then the last 2 lines repeat for about 50 lines, the nothing more is logged until the reboot }}}

SYSTEM NOTES
microcode: Microcode Update Driver: v2.00 <tigran@aivazian.fsnet.co.uk>, Peter Oruba
No overclocking
Inside thoroughly vacuumed regularly, no dust blocking heatsink, all temperatures in good range
lspci -k viewable here: http://pastebin.ca/3160329
lsusb viewable here: http://pastebin.ca/3160278
lsusb -t viewable here: http://pastebin.ca/3160279
Single hard drive, passes extensive testing, btrfs
Most recent motherboard BIOS - MSI X99S SLI PLUS (1.8 3/20/2015)
Most recent VGA BIOS - XFX nVidia GeForce GT 640 2GB (7/14/2012)

SYSTEM SPECIFICATIONS
DMI: MSI MS-7885/X99S SLI PLUS (MS-7885), BIOS 1.80 03/20/2015
Haswell-E -- smpboot: CPU0: Intel(R) Core(TM) i7-5820K CPU @ 3.30GHz (fam: 06, model: 3f, stepping: 02)
Linux version 4.1.6-1-ARCH (builduser@tobias) (gcc version 5.2.0 (GCC) ) #1 SMP PREEMPT Mon Aug 17 08:52:28 CEST 2015
Memory: 32840088K/33447336K available (5699K kernel code, 893K rwdata, 1732K rodata, 1180K init, 1152K bss, 607248K reserved, 0K cma-reserved)
06:00.0 VGA compatible controller: NVIDIA Corporation GK107 [GeForce GT 640] (rev a1)
Model=TOSHIBA MD04ACA500, FwRev=FP2A --- Plugged into motherboard SATA, no SATA controllers
KDE plasma-desktop/workspace 5.4.1-2
nouveau driver 1.0.11-3