Nouveau support can be dropped (Prime offloading is the better thing)

[karolherbst]

If you want to use your nvidia card you should use Prime offloading as described there: https://nouveau.freedesktop.org/wiki/Optimus/

And if a user has a too old Kernel for that, then he will run into different issues and also can't get a faster PCIe link than 2.5, which really has a big performance hit with bumblebee so the performance is bad either way (not so bad with PRIME offloading).

There is really no need to still maintain the nouveau bumblebee code afaik.

[ArchangeGabriel]

How do you switch fastly from nouveau to nvidia and back for testing purposes? I can do that with Bumblebee, but not Bumblebee + Prime AFAIK. Because if PRIME is on, Bumblebee can’t work, right?

[Lekensteyn]

Ack, nouveau is a good replacement for Bumblebee + bbswitch since it provides both PRIME support and runtime PM (if it works). I see on #nouveau that you get quite some support requests mentioning nouveau and Bumblebee, either we keep support (but print a warning once) or remove it.

Using PRIME requires a restart of X (I don't think you can "hotplug" a driver in Xorg, can you?), so either you use Bumblebee and get the blob for acceleration + bbswitch for power saving or do not use Bumblebee and use nouveau for acceleration + bbswitch + external monitor support.

Is this assessment correct?

[karolherbst]

@ArchangeGabriel no problem. I have bumblebeed running all the time and just load nouveau when I need to. Actually you will need DRI3, so you won't need the nouveau DDX, otherwise yeah, it is messy.

But I can unload/load nouveau at any time without restarting X and also run something with bumblbee (after I unloaded nouveau and turned it off via bbswitch)

[karolherbst]

@Lekensteyn not with DRI3, but you need a hacky xorg.conf:

Section "ServerFlags"
        Option      "AutoAddGPU" "false"
EndSection

Section "Device"
    Identifier "IntelCard"
    Driver "intel"
    Option "DRI" "3"
EndSection

Section "Device"
        Identifier "nvidia"
        Driver "dummy"
        BusID "PCI:01:00:0"
EndSection

[karolherbst]

well with Dri3 you also don't get vdpau offloading, but well...

[Lekensteyn]

@karolherbst Hmm, maybe I should have said hotplugging a device. As far as I know, if the graphics card is off during the start of X (normal case with Bumblebee), then X won't pick it up and interfere. Assume that I use Bumblebee and then decide to try nouveau + PRIME, then somehow Xorg must somehow pick up this device after loading.

[karolherbst]

@Lekensteyn with DRI3 it doesn't need to be picked up by X. X simply doesn't matter.

[ArchangeGabriel]

@karolherbst Not sure to understand the whole thing. Without the Xorg conf file you gave above, when modprobing nouveau (after echoing ON to bbswitch), I still get no other providers than the Intel one. I suppose that in order for this to work, I need the above Xorg conf snippet. Can test it right now, but does it work with the card being off at startup? Are there any drawbacks?

[karolherbst]

@ArchangeGabriel with DRI3 prime offloading you don't need to setup the offloader thing anymore (and it won't get listed in --listproviders anyway). It just works out of the box, because a kernel drm API is being used in this case.

The xorg.conf file is just there (especially the dummy part), so that Xorg won't grab the nvidia gpu and makes unloading nouveau impossible (because the nouveau DDX would hold a reference to the driver)

and the DRI 3 part is there to actually enable DRI3 for the intel DDX.

[karolherbst]

well there are still some DRI2 only things like reverse prime (using display port on nvidia GPU) and VDPAU offloading, but that's something bumblebee doesn't support anyway, so you are better of Prime here.

[ArchangeGabriel]

Awesome! So OK, my previous session must have been bogus for some reason because DRI_PRIME=1 glxinfo was still returning Intel even after echoing ON to bbswitch and modprobing nouveau, but now it works fine and I can even run UT4 without crashing on startup. Obviously, there is still the great perf issue from reclocking, which amounts to better perfs on my Intel HD4600 than Nvidia Geforce GT750M, but with all your great work in that area, it should be working in a near future. ;)

So, here is my proposal: add a new backend in Bumbleblee, named prime (optirun -b prime), that only works with nouveau under DRI3 Intel (must add checks for this), and basically just turn ON the card, modprobe nouveau, set DRI_PRIME=1 and fire. On exit, unload nouveau, turn OFF the card. So, that’s quite like none, shouldn’t be hard to implement (biggest part is checks I think). What do you think about it?

And then, advertises people wanting to use nouveau to use that.

The main difference versus raw PRIME is PM: bbswitch vs nouveau. Also, since the card is OFF at startup, you don’t need any special xorg conf file (except DRI3, which could become the default one day).

[ArchangeGabriel]

In fact, closer to --no-xorg than -b none.

[karolherbst]

if you want to add a prime backend, then also pass runpm=0 to nouveau. Usually nouveau should take care of turning off/on the gpu itself

[ArchangeGabriel]

Sure, in fact we should ever do that when using bbswitch.