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

Fri Oct 30 15:54:47 UTC 2015

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
> > > >      
> > > >
> > > > _______________________________________________
> > > > vfio-users mailing list
> > > > vfio-users at redhat.com
> > > _______________________________________________
> > > vfio-users mailing list
> > > vfio-users at redhat.com
> > > https://www.redhat.com/mailman/listinfo/vfio-users
> > _______________________________________________
> > vfio-users mailing list
> > vfio-users at redhat.com
> > https://www.redhat.com/mailman/listinfo/vfio-users
> > 
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