[vfio-users] [FEEDBACK NEEDED] Additionnal tips to include in the Arch wiki article

[Nicolas Roy-Renaud]

What part of the article are you referring to and how exactly does it 
improve performance for you?

- Nicolas

On 2016-05-21 11:42, Colin Godsey wrote:
> Windows 10 forcing X2APIC: https://support.microsoft.com/en-us/kb/2303458
>
> This helped a bunch for me at least on 4.4- I think there was some 
> confusion on the correct way to signal the guest on what APIC to use, 
> forcing this gave me much better %sys times. AFAIK it can also still 
> be used with hyper-v APIC because that’s just the EOI 
> para-virtualization.
>
> On Fri, May 20, 2016 at 2:28 PM Alex Williamson 
> <alex.l.williamson at gmail.com <mailto:alex.l.williamson at gmail.com>> wrote:
>
>     On Fri, May 20, 2016 at 11:38 AM, Nicolas Roy-Renaud
>     <nicolas.roy-renaud.1 at ens.etsmtl.ca
>     <mailto:nicolas.roy-renaud.1 at ens.etsmtl.ca>> wrote:
>
>         Did you have any issues with efifb or some other driver
>         grabbing the gard before vfio-pci? What are your IOMMU groups
>         like, which chard is your boot_vga, what script or method do
>         you use to get vfio-pci to bind with your card, what's your
>         kernel command line and what modules are included in your
>         initramfs?
>
>         I've struggled with getting my primary GPU to work correctly
>         for a passthrough like this, and I ended up switching it up
>         with the secondary because I simply couldn't get it to work
>         properly (I'd keep getting something about "|Invalid ROM
>         contents|") and I couldn't see my boot logs until the host
>         driver finished loading. It's really inconvenient now becuase
>         my motherboard is designed so that having a full-size GPU in
>         the second PCIe slot blocks 4 SATA ports out of 6, so I need
>         to have L-shaped cables in a bunch of places to make
>         everything work properly.
>
>
>     The boot VGA ROM is handled differently from other PCI ROMs in
>     Linux, when you read it you're actually reading a shadow copy of
>     it placed at 0xc0000, which has its roots back in the original IBM
>     PC history. Execution of the VGA ROM is allowed to modify this
>     copy of the ROM image in memory.  Thus you're really not getting a
>     pristine copy of the device ROM and it can often lead to these
>     invalid ROM contents messages.  I wish we provided raw access to
>     the PCI option ROM in these cases as well.  For now, if you do
>     have these sorts of invalid ROM messages, I would suggest that you
>     at least boot with the card as secondary, dump the ROM, then use
>     that collected image with the romfile= option rather than use the
>     shadow copy.  I had to add some code to vfio to fix device IDs and
>     checksums for IGD assignment because of this, I don't know if
>     there's any standard fixup we can do for other vendors.  Thanks,
>
>     Alex
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