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Thread: QEMU 1.5 Supports VGA Passthrough, Better USB 3.0

  1. #11
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    Quote Originally Posted by curaga View Post
    This is different. This is for when you have two graphics cards, and are dedicating one to the VM.
    I guess it wouldn't be feasible for the host to give up the card and then take it back again when the guest is done? X would probably need to be stopped at the least.

  2. #12
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    Quote Originally Posted by curaga View Post
    This is different. This is for when you have two graphics cards, and are dedicating one to the VM.
    Oh, so basically this is useless.

  3. #13
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    Hmm, interesting... So if I have a HDG 2500 and a GTX 660, I could boot to desktop using HDG 2500, then when needed start QEMU, which would then make use of all the functionality the GTX 660 offers?

  4. #14
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    Quote Originally Posted by uid313 View Post
    Oh, so basically this is useless.
    Why is this useless? Most x86 based computers today have an IGP and a discrete GPU, yet one of them is almost always inactive. Give the better one to your VM and problem solved.


    I think 1 thing people should be aware of is if this VGA passthrough is anything like the one from other VMs, IOMMU support will be needed, which is a relatively uncommon feature.

  5. #15
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    Quote Originally Posted by schmidtbag View Post
    I think 1 thing people should be aware of is if this VGA passthrough is anything like the one from other VMs, IOMMU support will be needed, which is a relatively uncommon feature.
    Got that covered. It's called VT-d on Intel and AMD-Vi on AMD. And it's not really that uncommon on current hardware.

  6. #16
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    Quote Originally Posted by GreatEmerald View Post
    Got that covered. It's called VT-d on Intel and AMD-Vi on AMD. And it's not really that uncommon on current hardware.
    Finding a motherboard that really supports it is a pain.
    I have 4 motherboards here all with IOMMU mode and it doesn't work on any of them.

  7. #17
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    Quote Originally Posted by GreatEmerald View Post
    Got that covered. It's called VT-d on Intel and AMD-Vi on AMD. And it's not really that uncommon on current hardware.
    Oh, I think it's quite uncommon. Especially on Intel processors. You need a Xeon processor and the corresponding mainboard. For AMD also not all chipsets support it. Which is rather strange, because I would have though it's enough for the processor to support it, since the memory controller is now part of the processor. In any case, it's often hard to find out whether particular mainboard supports it. I often have to download the manual to take a look at the BIOS options.

    It's similar to the situation with ECC. For intel it's mostly Xeon processors that support it. Strangely enough, there are some Pentium/Core-i3 processors that support it too but need the appropriate mainboard (C200 series chipset) which quite a bit more expensive. AMD AM3+ processors support ECC but there are some motherboards that don't. I imagine they just lack the traces to the additional pins for the ECC DIMM. But finding trustworthy information is quite hard. Apparently, most people dont give a shit about IOMMU/ECC. They need to know what they are first...

  8. #18
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    Quote Originally Posted by schmidtbag View Post
    Why is this useless? Most x86 based computers today have an IGP and a discrete GPU, yet one of them is almost always inactive. Give the better one to your VM and problem solved.
    Most of the ultrabooks I've looked at just have Ivy Bridge, and you pay a premium in both normal laptops and ultrabooks to get a discrete card alongside it. Of course, if your purpose is to run Linux with Windows on QEMU intermittently for graphics-intensive proprietary apps, you could plan to buy one of these systems specifically for that purpose. And of course it's useful in that case- no need to dual-boot most likely, unless you're a stickler for getting every ounce of performance.

    I'm just waiting to see whether this can apply more broadly or split a single GPU's resources. My guess is that it's either non-trivial or it's basically impossible without the right graphics chip architecture.

  9. #19
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    Quote Originally Posted by kobblestown View Post
    Oh, I think it's quite uncommon. Especially on Intel processors. You need a Xeon processor and the corresponding mainboard. For AMD also not all chipsets support it. Which is rather strange, because I would have though it's enough for the processor to support it, since the memory controller is now part of the processor. In any case, it's often hard to find out whether particular mainboard supports it. I often have to download the manual to take a look at the BIOS options.
    What are you talking about? I have an i5-3470, and it supports VT-d. It's fairly high-end, but by far not uncommon, and definitely not a Xeon. Other processors that support it are i5-3550, i5-3330, i5-2500... Heck, even a i5-680 supports it. It's not uncommon in the slightest.

    I also have a MSI B75A-G43 motherboard, and guess what, it supports VT-d as well. Even some Core 2 motherboards support it. So it's again not uncommon, although it's true that it's usually not advertised that much.
    Last edited by GreatEmerald; 05-21-2013 at 01:32 PM.

  10. #20
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    @sonicspectre
    Well the only way to divide GPU power between a VM is through the old method of creating a virtual GPU, which we all know is limiting and doesn't perform all that great.


    Quote Originally Posted by GreatEmerald View Post
    What are you talking about? I have an i5-3470, and it supports VT-d. It's fairly high-end, but by far not uncommon, and definitely not a Xeon. Other processors that support it are i5-3550, i5-3330, i5-2500... Heck, even in i5-680 supports it. It's not uncommon in the slightest.

    I also have a MSI B75A-G43 motherboard, and guess what, it supports VT-d as well. And even some Core 2 motherboards support it. So it's again not uncommon.
    VT-d is extremely common. The version of VT-d that supports IOMMU is not, and IOMMU is required for GPU passthrough:

    http://en.wikipedia.org/wiki/List_of...rting_hardware

    This list is relatively small. Albeit, the motherboard sections are a bit incomplete. My motherboard is one of the only AMD desktop boards with IOMMU support and it isn't on this list (890FX chipset).
    Last edited by schmidtbag; 05-21-2013 at 01:37 PM.

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