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#1 2011-11-30 18:05:33

vpoinot
Member
Registered: 2009-04-09
Posts: 19

Linux, SandyBridge and Optimus

Hi,

I need to buy a new laptop and I would like to see clear in this Optimus thing before doing so.
To summarize, here is what I understood:
- Intel SandyBridge processors have an integrated GPU,
- most laptops (all?) come with a "discrete" GPU as well (be it Nvidia or AMD, or anything else)
- this means these laptops basically have two GPUs. X cannot cope with this, unless going through tremendous pain with Bumblebee, Ironhide and the likes. And even going this route, crashes, freezes, are very likely.

How to avoid this? Essentially, a drastic solution is to have only one GPU, so:
- turn off Intel IGP: is this possible? my understanding is that the IGP sits in front of the Nvidia GPU, and that the latter needs the former: am I right?
- turn off discrete GPU: apparently this is possible via some acpi_call, which is dangerous, does not always work, etc. Or sometimes, directly from the BIOS. How do I know, before buying the laptop, if the BIOS provides this possibility? Do I have to go to the shop and ask the sales rep to reboot his machines so that I can have a look? I doubt he will agree...

Some things I don't understand:
1) what happens for laptops equipped with a SandyBridge processor and an AMD card: do AMD cards have some technology similar to Optimus? I guess this combination is just as bad as SandyBridge/Nvidia, right?
2) what about laptops with an AMD processor and any other GPU: this should be fine, correct? Or do AMD processors also integrate an IGP? Of course, problem is that AMD processors seem to be way behind Intel's, in terms of performance...

Also, I tend to think I don't need a poweful GPU, because I don't play. Would Intel's IGP be enough for all kinds of 3D effects one can find in KDE these days? What about watching HD movies? What about Flash animations? Does this require a graphics card?

That's a lot of questions, but as I said, I don't want to spend a good deal of money for a machine that just does not work...

Thanks.

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#2 2011-11-30 19:20:13

t4k1t
Member
Registered: 2009-07-19
Posts: 123

Re: Linux, SandyBridge and Optimus

Hey,

on my laptop I only use the Intel GPU and I have no problems at all with HD movies or flash.
Can't say anything about turning the other GPU off though, because I simply never installed the nvidia-drivers and since I don't use it mobile that much I don't really care that my Nvidia card is still activated.
I also don't know about KDE effects for sure but I really doubt that you will have problems with them even when you only use the Intel GPU.


Who we are is but a stepping stone to what we can become...

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#3 2011-11-30 19:28:35

alphaniner
Member
From: Ancapistan
Registered: 2010-07-12
Posts: 2,807

Re: Linux, SandyBridge and Optimus

vpoinot wrote:

How do I know, before buying the laptop, if the BIOS provides this possibility? Do I have to go to the shop and ask the sales rep to reboot his machines so that I can have a look? I doubt he will agree...

Go to the manufacturer's site and look for a manual.  IDK about laptops, but most desktop motherboards have a detailed BIOS section in the manual.


But whether the Constitution really be one thing, or another, this much is certain - that it has either authorized such a government as we have had, or has been powerless to prevent it. In either case, it is unfit to exist.
-Lysander Spooner

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#4 2011-11-30 21:24:12

Tzbob
Member
From: Belgium
Registered: 2011-04-12
Posts: 61

Re: Linux, SandyBridge and Optimus

I have a i7 Sandy bridge cpu with a 540GTM from Nvidia, I always turn off my discrete graphics using acpi-call(never had any problems with it).

As far as power goes, I don't use KDE so I can't comment on that but I can run simple games(Armagetronad) and videos on my native(1920x1080) resolution. Flash videos on linux are a pita and aren't gpu accelerated(correct me if im wrong) but a sandy bridge i7 cpu has no problems with 1080p youtube content.

The bios switch is only optional if the hardware allows it, as you already mentioned mose of the optimus laptops need the intel gpu to forward data to the screen and/or ports. I think Lenovo and some Alienware laptops are the only ones with such a hardware switch but I could be wrong.

There is a project called bumblebee which is basically optimus for linux, it's in beta phase(I think) but it's promising and it's working! Basically it lets the Nividia gpu do the computing and the intel igp do the forwarding.

As far as I know AMD has less problems on linux, I don't think they have a technique like optimus which uses both graphic cards, I'm pretty sure they either use on or the other. For switching between igp or AMD discrete I think vga_switcheroo was made? You'd have to look into that.

PS: I'm using a Dell l502x, it's quite a pain because the hdmi output is on the Nvidia card, the mini displayport is on the intel IGP and it has no vga, so definitely look into that before you buy your laptop.

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#5 2011-12-01 10:27:28

MadCat_X
Member
Registered: 2009-10-08
Posts: 157

Re: Linux, SandyBridge and Optimus

The way I understand it Optimus puts Intel and nVidia GPU in a "chain" where the Intel GPU draws on the screen and the nVidia GPU draws into Intel's GPU framebuffer - the Intel GPU cannot be disabled.

I have a limited experience with a SNB Lenovo laptop with HD3200 and GT520M. Since I couldn't get bumblebee working in Arch, I ended up disabling the nVidia GPU in BIOS. The laptop worked perfectly running KDE 4.7, desktop effects seemed smooth and some limited gaming was also possible. Flash videos seemed to be accelerated to some extent, at least the guy who's using it hasn't complained about laggy playback so far. I can't say much about the power consumption, but AFAICT the laptop looked like it could get near the advertised 3,5 hours battery life with forcibly enabled ASPM and RC6.
Definitely do some research before you get a SNB based laptop, but even though there are some issues I consider SNB very good deal if you want to run Linux on a laptop.

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#6 2011-12-01 17:04:12

vpoinot
Member
Registered: 2009-04-09
Posts: 19

Re: Linux, SandyBridge and Optimus

Thanks for your replies.

@t4k1t: I am surprised, it seems that even though you did not disable your nvidia card, you have no problem running Linux. Is it enough not to install nvidia drivers to avoid any conflict and issue? It makes sense indeed, but I had not thought about this simple fact...

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#7 2011-12-01 18:12:10

Tzbob
Member
From: Belgium
Registered: 2011-04-12
Posts: 61

Re: Linux, SandyBridge and Optimus

vpoinot wrote:

Thanks for your replies.

@t4k1t: I am surprised, it seems that even though you did not disable your nvidia card, you have no problem running Linux. Is it enough not to install nvidia drivers to avoid any conflict and issue? It makes sense indeed, but I had not thought about this simple fact...

It should be enough. You don't have to disable the card, I just do it to lower power consumption.

Even if you can't boot because of autoloaded modules you can still blacklist them, problem solved.

Last edited by Tzbob (2011-12-01 18:35:08)

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