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

Fri Oct 30 14:39:25 UTC 2015

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_repositories#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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