[vfio-users] KVM options and the effect on performance

Fri Oct 30 19:34:00 UTC 2015

These cases seem to vary a great deal from one setup to another. I'm not 
looking to start yet another flamewar here but I found setting up a 
HD7970 guest really easy and Windows insider preview has been stable 
experience. I've been playing dishonored on 1080p with everything high 
with a good performance.

I'm going to upgrade my gpu when I get either Vive or Oculus rift - 
haven't decided yet what gpu to buy. One thing is sure: it has to work 
with VGA passthrough.

IGP on host, i7-4790, debian testing with 4.2.0-1

a_a

On 30.10.15 17:54, Mark Weiman wrote:
> I use an Intel iGPU for my host and a GTX 760 for my guest and it plays
> the games I play (Counter-Strike: Global Offensive, Rocket League, ...)
> just fine.  It also runs other operating systems just fine.
>
> I have had no configuration issues with my Nvidia card, but in the
> past, AMD cards usually gave me hell (outside of this context, usually
> was catalyst's fault) and is why I do not purchase them anymore.
>
> Mark Weiman
>
> On Fri, 2015-10-30 at 22:39 +0800, Eddie Yen wrote:
>> I'm using GTX480 & GTX980 for now. GTX480 used by host and another
>> one used by guest.
>> GTX980 works very well in guest, tested 3 major games (Assassin's
>> Creed: Unity, Crysis 3, and GTA5), and all works well.
>> The only problem is that I need to add KVM Hidden State=on and
>> qemu:commandline to adding Hyper-V specs.
>>
>> QEMU will support Hyper-V that override NVIDIA driver detection, but
>> I don't know how long will support on libvirt and virt-manager.
>>
>> 2015-10-30 22:13 GMT+08:00 Ryan Flagler <ryan.flagler at gmail.com>:
>>> Thanks for the config examples. What GPU's do you guys use? I'm
>>> struggling with 2 different AMD Radeon models (7850 and R9 380).
>>> Early on in my research I noticed people saying Radeons were easier
>>> to get working, but the deeper I dig, it seems nVidia cards have
>>> some initial quirks, but are more stable. Hopefully next week I'll
>>> get some time to tweak my setup more.
>>>
>>> On Thu, Oct 29, 2015 at 11:15 PM Dan Ziemba <zman0900 at gmail.com>
>>> wrote:
>>>> I'll also throw in the scripting I used to use before switching
>>>> to
>>>> libvirt a month or so back.  The latest version is with the
>>>> default
>>>> i440 machine, but if you look back in the history some you can
>>>> see how
>>>> I was using q35 before.
>>>>
>>>> https://github.com/zman0900/qemu-vifo
>>>>
>>>> -----Original Message-----
>>>> From: Mark Weiman <mark.weiman at markzz.com>
>>>> To: Ryan Flagler <ryan.flagler at gmail.com>, vfio-users at redhat.com
>>>> Subject: Re: [vfio-users] KVM options and the effect on
>>>> performance
>>>> Date: Fri, 30 Oct 2015 00:00:21 -0400
>>>>
>>>> To be honest, I have found little to no real noticeable
>>>> difference
>>>> between many of them.  My VMs usually use a qcow2 image that are
>>>> mounted via virtio.
>>>>
>>>> As for a CPU, I use an i7-4970K and it works beautifully.  It
>>>> really
>>>> boils down to when you choose your hardware whether or not you've
>>>> done
>>>> the research beforehand so you can have a good time rather than
>>>> fighting it.  If I were to build my main rig again, I would have
>>>> looked
>>>> closer into the motherboard so I wouldn't have to patch my
>>>> kernel,
>>>> although it really is not a problem to do with that CPU (I also
>>>> provide
>>>> a slightly modified version of Dan Ziemba's PKGBUILD [1] that
>>>> includes
>>>> the i915 and acs patch from my Arch Linux repository [2]).
>>>>
>>>> As for your Wiki idea, since this all is open source software,
>>>> there is
>>>> nothing preventing you from contributing to documentation on
>>>> this.  The
>>>> Arch Linux Wiki does provide a lot of information on how to do
>>>> all of
>>>> this [3] and can guide you even if you aren't using Arch Linux.
>>>> Just
>>>> change the Arch specific bits to whatever distribution you use.
>>>>
>>>> If it helps, this is the script I use when I run my Windows 10 VM
>>>> [4].  It's really sloppy, but it seems to work for me.
>>>>
>>>> As for using btrfs to store images, I use it to store my images
>>>> and I
>>>> have had no issue.  It just has to be pointed out that btrfs is
>>>> still
>>>> under development, so you should just put that under
>>>> consideration.
>>>>
>>>> Didn't want to leave ya hangin,
>>>> Mark Weiman
>>>>
>>>> [1] https://aur.archlinux.org/packages/linux-vfio-lts
>>>> [2] https://wiki.archlinux.org/index.php/Unofficial_user_reposito
>>>> ries#m
>>>> arkzz
>>>> [3] https://wiki.archlinux.org/index.php/PCI_passthrough_via_OVMF
>>>> [4] http://info.markzz.com/kvm-start.sh
>>>>
>>>> On Thu, 2015-10-29 at 16:50 +0000, Ryan Flagler wrote:
>>>>> Hey everyone, sorry if I'm doing this wrong, this is my first
>>>> time
>>>>> using a mailing list. (Side note, if anyone has a better way to
>>>> view
>>>>> historical emails than the web page, please let me know)
>>>>>
>>>>> I've been tinkering with KVM for a bit on my system and had
>>>> some
>>>>> general performance questions to ask. I see a lot of people
>>>> doing VGA
>>>>> passthrough using the q35 chipset instead of the i440FX
>>>> chipset. I've
>>>>> personally had no luck getting q35 to be stable for me, and
>>>> I've seen
>>>>> some people say it's not worth the headache. But the big
>>>> question to
>>>>> me, is there a performance difference with CPU, VGA, memory
>>>> etc.
>>>>> using q35? I'm not looking for specifics, but I'm curious about
>>>> the
>>>>> following qemu parameters.
>>>>>
>>>>> Which chipset emulation performs better and in what areas?
>>>>> q35 vs i440fx
>>>>>
>>>>> What is the best way to pass a disk through to a VM to get the
>>>> most
>>>>> performance?
>>>>> .img file, /dev/sd[x] disk, virtio-scsi, etc.
>>>>>
>>>>> What is the best way to handle networking?
>>>>> virtio-nic, hardware passthrough, bridge, nat, etc.
>>>>>
>>>>> What is the best way to assign CPUs?
>>>>> cpu pinning, assigning host cpu parameters, etc.
>>>>>
>>>>> Does the BIOS have an effect on performance?
>>>>> seabios vs OVMF?
>>>>>
>>>>> CPU/Chipset IOMMU support - Not necessarily performance
>>>> related, but
>>>>> stability?
>>>>> e5 vs e3 vs i7 vs cpu architecture etc. What things are good to
>>>> look
>>>>> for, what are bad? Etc.
>>>>>
>>>>> What would be interesting, especially as a new KVM/Qemu user,
>>>> would
>>>>> be to see an entire wiki/performance page with examples and
>>>>> specifics. It's hard to filter through all the various pages of
>>>> VM
>>>>> options where people don't really explain why they're doing
>>>> something
>>>>> the way they are.
>>>>>
>>>>> Examples:
>>>>>
>>>>> Disk Options
>>>>> Best
>>>>> -device virtio-scsi-pci,id=scsi
>>>>> -drive file=/dev/sd[x],id=disk,format=ls raw,if=none -device
>>>> scsi-
>>>>> hd,drive=disk
>>>>>
>>>>> Better
>>>>> -device virtio-scsi-pci,id=scsi
>>>>> -drive file=/opt/[vm_name].img,id=disk,format=raw -device scsi-
>>>>> hd,drive=disk
>>>>>
>>>>> Good
>>>>> -drive file=/opt/[vm_name].img,id=disk,format=raw -device ide-
>>>>> hd,bus=ide.0,drive=disk
>>>>>
>>>>> And maybe an overall explanation of why one is better over the
>>>> other.
>>>>> I know this may not exist and I'm not asking a single person to
>>>> do
>>>>> the leg work, but being new to this, it's hard to focus on the
>>>> pieces
>>>>> that matter vs just using the first thing I find that works. If
>>>> there
>>>>> is a "right" place to start something like this I'd be happy to
>>>> setup
>>>>> a generic page where more experienced people could easily
>>>> contribute.
>>>>>
>>>>> Thanks - Ryan
>>>>>
>>>>>
>>>>> _______________________________________________
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>>>>> vfio-users at redhat.com
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