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Getting an Nvidia GT 750M to suspend properly with BumbleBee

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There's a problem getting the Nvidia card to wake up after a suspend, apparently. I discovered this during development of some Theano / libgpuarray stuff (where the programming environment was tiresome to keep rebuilding). Until I found the fix, the only way to regain the Nvidia card was to reboot the machine.

So : Before suspending, execute the following commands as root :

# Check whether Nvidia card is 'live' :
cat /proc/acpi/bbswitch

# If that shows ON, then try :
tee /proc/acpi/bbswitch <<<OFF
cat /proc/acpi/bbswitch

# If it still shows ON, then :
optirun --no-xorg modprobe -r nvidia
cat /proc/acpi/bbswitch

# Should definitely show OFF by now...

Then the laptop can be safely suspended, and optirun (the regular bumblebee invocation) will resurrect the GPU.

NB: It's a good idea (if you're just using the GPU for 'compute') to use optirun --no-xorg since that simplifies the number of different processes with their fingers clutching at your GPU.

Pre-suspend hook

As root, create a file /usr/lib/systemd/system-sleep/turn-off-gpu.sh with the following contents (change the username path to somewhere relevant) :

#!/bin/bash
[ "$1" = "pre" ] && {
  LOG=/home/username/sleep.log

  D=`date`
  echo "${D} :: Pre-'$2'" >> ${LOG}

  echo -n "  GPU state before      : " >> ${LOG}
  cat /proc/acpi/bbswitch >> ${LOG}

  optirun --no-xorg modprobe -r nvidia >> ${LOG}

  echo -n "  GPU state modprobe -r : " >> ${LOG}
  cat /proc/acpi/bbswitch >> ${LOG}

  sleep 1

  echo -n "  GPU state after wait  : " >> ${LOG}
  cat /proc/acpi/bbswitch >> ${LOG}
}
exit 0

(Remember to chmod 755 /usr/lib/systemd/system-sleep/turn-off-gpu.sh after creating it.)

To test (without suspending) try /usr/lib/systemd/system-sleep/turn-off-gpu.sh pre suspend-test, and check for new entries in the file /home/username/sleep.log : You should get an entry like ::

Wed Nov 26 16:06:28 SGT 2014 :: Pre-'suspend-test'
  GPU state before      : 0000:01:00.0 ON
  GPU state modprobe -r : 0000:01:00.0 ON
  GPU state after wait  : 0000:01:00.0 OFF

(with the final 'OFF' being the verification that it's now safe for the suspend to take effect).

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