[Nix-dev] Experiences with Nvidia Optimus?

[Arie Middelkoop]

On 05-02-12 09:16, Mathijs Kwik wrote:
> On Sun, Feb 5, 2012 at 2:11 AM, Arie Middelkoop<amiddelk at gmail.com>  wrote:

>> The main advantage of the package actually arises when you don't use the
>> card: it uses ACPI to shutdown the card, which - depending on what card you
>> have - saves quite a bit of energy / heat.
>> (also available as separate kernel module)
>
> I haven't looked at bumblebee yet, your comments seem to indicate I
> don't need it if I just load bbswitch and discrete_vga_poweroff on
> startup.
> Or is it any use besides that yet?

I'm not entirely sure. I've used bbswitch at startup for a week. With a 
modprobe option, you can tell it to shutdown the card directly when the 
module is loaded, but that didn't work very well (maybe because some 
subsystem first had to be initialized or so). It did work to turn off 
the card using a job just after udev.

I read somewhere that you should also turn on the card on shutdown. I 
didn't do that, and so far, I had only one hard lockup on shutdown, but 
that may be unrelated.

Anyway, if you run the bumblebeed daemon, it takes care of this. It also 
unloads the nvidia module before shutting down the card (and actuall 
requires the nvidia module to be loaded on startup), and saves/restores 
'the pci configuration space' (whatever that is). Anyway, that seems to 
work fine, but it's ofc a bit overkill to have a process running for 
only this purpose.

For the near future, I've heard that the bbswitch module has been ported 
to the nouveau driver as part of switcheroo. That would be a more 
cleaner solution, although I'd not bother with it now.

> I haven't used any non-kernel-provided modules on nixos before.
> I now have this in configuration.nix:
>
> boot = {
>    kernelPackages = pkgs.linuxPackages_3_2;
>    extraModulePackages = [ config.boot.kernelPackages.bbswitch ];
>    kernelModules = ["acpi-cpufreq" "kvm-intel" "bbswitch"];
> };
>
> That takes care of loading the module itself.

Yes, that corresponds exactly to what I'm having.

> But I need to put config.boot.kernelPackages.bbswitch in
> systemPackages too, to get the discrete_vga* helpers.
> Is this how it's supposed to work?

That'd work I guess. I simply put the one "echo" line of the helper into 
an upstart job (with 'task = true;' so that it only runs it once). 
Unfortunately, I deleted it from my configuration.nix, but it should be 
easy to reproduce.

> Oh and slightly offtopic: I found the intel microcode package you
> provided but I can't find out if it works.
> Without it, modprobe microcode (the microcode loader) produces the
> same dmesg output as with microcodeIntel included in
> hardware.firmware.
> No indication of it finding the .dat file, or using it (or skipping
> because not applicable to my cpu).
> How can I find out if it's any use?

Sorry, this was exactly the issue that I wanted to investigate somewhere 
today. Some documentation seemed to suggest that the .dat file just has 
to be put in the firmware, and the module loaded. The sourcecode of the 
'microcode' module seems to suggest something different actually. My 
guess is that some userspace tool needs to be involved or so.

Anyway, I'm not sure whether the microcode is of any use in the first 
place. My kernel log seems to suggest that it may be relevant for me, 
but I don't think it's important. Also, it may very well be that the 
bios already updates the microcode.

Then again, I experienced quite some instabilities with my new laptop, 
so I should probably check these things. So far, using the latest 3.2 
kernel already helped a great deal.

Arie