[CentOS-virt] libvirt, xen PV, qemu-system-i386, root user

Sat Sep 12 08:51:39 UTC 2015
Pasi Kärkkäinen <pasik at iki.fi>

On Sat, Sep 12, 2015 at 01:35:48AM +0200, Karel Hendrych wrote:
> Comparing simple dd bs=1M count=10000 on dom0 vs domU. Qemu driver
> is achieving pretty much the same like dom0.
>

So you're measuring buffered speed. Try measuring non-buffered (iflag=direct or oflag=direct, depending if you're reading or writing).

-- Pasi

> Thanks
> --
> Karel
> 
> On 7.9.2015 21:45, Pasi Kärkkäinen wrote:
> >On Mon, Sep 07, 2015 at 05:47:39PM +0200, Karel Hendrych wrote:
> >>...
> >>
> >>changing from: <driver name='file'/> to: <driver name='tap2'/> makes
> >>the domain start without QEMU.
> >>
> >>However I see much better performance with QEMU (close to dom0,
> >>tested using simple dd writes) than with tap2 driver. Is that
> >>expected?
> >>
> >
> >How did you measure it? buffered or direct io?
> >
> >
> >-- Pasi
> >
> >
> >>What's best practise to file based storage on latest CentOS6-xen
> >>(Kernel 3.18.17, Xen 4.4.2-7)
> >>
> >>Are there any guides around running QEMU on CentOS6-xen as non-root user?
> >>
> >>Cheers
> >>--
> >>Karel
> >>
> >>On 7.9.2015 17:42, Karel Hendrych wrote:
> >>>Hi, spot on!
> >>>
> >>>
> >>>On 6.9.2015 12:56, Pasi Kärkkäinen wrote:
> >>>>On Sun, Sep 06, 2015 at 09:08:50AM +0200, Karel Hendrych wrote:
> >>>>>Hi, after migrating to libvirt/libxl according to:
> >>>>>
> >>>>
> >>>>Hi,
> >>>>
> >>>>>https://wiki.centos.org/HowTos/Xen/Xen4QuickStart/Xen4Libvirt
> >>>>>
> >>>>>I've noticed that my Xen PV domains are being launched by
> >>>>>qemu-system-i386 running under root privileges.
> >>>>>
> >>>>>I am wondering why is this? Previously no qemu process was used.
> >>>>>
> >>>>>If qemu is needed for some reason, are there any guidelines for
> >>>>>non-root operation?
> >>>>>
> >>>>
> >>>>In general qemu is used for the following purposes:
> >>>>
> >>>>- for certain domU disk backend types (image files), and/or if there's
> >>>>no blktap driver in dom0 kernel.
> >>>>- domU graphical console (PVFB) VNC server, if it's enabled for the domU.
> >>>>
> >>>>
> >>>>>--
> >>>>>Karel Hendrych
> >>>>
> >>>>
> >>>>-- Pasi
> >>>>
> >>>>_______________________________________________
> >>>>CentOS-virt mailing list
> >>>>CentOS-virt at centos.org
> >>>>https://lists.centos.org/mailman/listinfo/centos-virt
> >>>>
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