[vfio-users] Windows 10 guest refuses to boot when passed my NVIDIA graphics card

[Alex Williamson]

On Tue, Sep 15, 2015 at 4:09 PM, Jasen Borisov <tajjada at gmail.com> wrote:

>
>
>
> On Wed, Sep 16, 2015 at 12:59 AM, Alex Williamson <
> alex.l.williamson at gmail.com> wrote:
>
>> On Tue, Sep 15, 2015 at 3:32 PM, Jasen Borisov <tajjada at gmail.com> wrote:
>>
>>> I managed to successfully boot Arch Linux in the VM. Turned out I wasn't
>>> patient enough. With enough waiting, the same VM configuration as before
>>> (including my passthrough NVIDIA *and* EHCI!) booted. But it is
>>> *incredibly* slow. Took over 10 minutes to get to a login prompt, and a
>>> couple of minutes to do its automatic root login. I plugged a USB keyboard
>>> into the hardware port on my PC that belongs to the EHCI controller I
>>> passed to the VM, and the keyboard worked as expected and I could type
>>> inside the VM. I managed to mount a filesystem and dump `dmesg` to a file,
>>> so I can get it on my desktop. Here is a pastebin of it:
>>> https://bpaste.net/show/e6970c05aff5
>>>
>>> This makes me think that *maybe* if I leave Windows to boot overnight,
>>> next morning I might be surprised by a desktop :)
>>>
>>> Anyway, it is unacceptably slow, and I would appreciate any help to
>>> improve the situation.
>>>
>>> I noticed a lot of errors regarding msrr, both in the host and guest
>>> dmesg, so I guess it would probably be a good idea to add that KVM option
>>> you mentioned. However, I doubt that that is the cause of the performance
>>> problems. When I remove all VFIO devices and replace them with emulated
>>> ones, Arch Linux is very fast (or rather, normal, just very fast in
>>> comparison) despite the same msrr errors appearing.
>>>
>>> Any ideas?
>>>
>>
>> What if you downgrade to kernel 4.1?
>>
>
> As I said, I want to run Windows inside the VM, not Linux. I am just
> testing with Linux to see if my VFIO setup is working. I am doing this
> because troubleshooting with Linux is a lot easier (due to information from
> things like dmesg) than with Windows. Once I know that VFIO is working fine
> on my system, I will set up a Windows guest. Hence, kernel
> regressions/bugs/features(?) in 4.2 that are not present in 4.1 are not
> something I particularly care about. That said, if downgrading to linux 4.1
> (not easy, because I was booting Linux from a live iso ... would have to
> either install or get an older live iso to do that) would help me figure
> out why my VM is slow and would provide worthwhile information, I would be
> happy to do it. By now, I have wasted a lot more time waiting for the slow
> VM to boot than it would take me to install Linux.
>

I'm asking about downgrading the *host* to v4.1.


>
>
>> The MTRR issue we've been battling generally resolves itself and the VM
>> runs at full speed once passed firmware.  I'll see if I can make my box act
>> this poorly.  Running 8 vCPUs on your system is surely not helping
>> performance, but this sounds like orders of magnitude worse than that.
>>
>
> Do you mean that having fewer vCPUs will somehow be better for
> performance? That seems counterintuitive ... I thought otherwise....
>
> Well, my physical CPU has 8 physical cores with hyperthreading, so 16
> logical cores. I thought it would make sense to give half of that to the VM
> and have the rest available for the host. By saying that it is "not helping
> performance", do you mean that there is some sort of significant overhead
> involved with having more vCPUs?
>

The XML I see in the first post is using 16 vCPU, leaving none for the host.
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