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

[Ryan Flagler]

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
> >
> >
> > _______________________________________________
> > vfio-users mailing list
> > vfio-users at redhat.com
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