CentOS virt - Sep 2015 - libvirt, xen PV, qemu-system-i386, root user

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 K?rkk?inen 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
> >>
> _______________________________________________
> CentOS-virt mailing list
> CentOS-virt at centos.org
> https://lists.centos.org/mailman/listinfo/centos-virt

Comparing simple dd bs=1M count=10000 on dom0 vs domU. Qemu driver is 
achieving pretty much the same like dom0.
Thanks
--
Karel

On 7.9.2015 21:45, Pasi K?rkk?inen 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 K?rkk?inen 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
>>>>
>> _______________________________________________
>> CentOS-virt mailing list
>> CentOS-virt at centos.org
>> https://lists.centos.org/mailman/listinfo/centos-virt
> _______________________________________________
> CentOS-virt mailing list
> CentOS-virt at centos.org
> https://lists.centos.org/mailman/listinfo/centos-virt
>

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 K?rkk?inen 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 K?rkk?inen 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
> >>>>
> >>_______________________________________________
> >>CentOS-virt mailing list
> >>CentOS-virt at centos.org
> >>https://lists.centos.org/mailman/listinfo/centos-virt
> >_______________________________________________
> >CentOS-virt mailing list
> >CentOS-virt at centos.org
> >https://lists.centos.org/mailman/listinfo/centos-virt
> >
> _______________________________________________
> CentOS-virt mailing list
> CentOS-virt at centos.org
> https://lists.centos.org/mailman/listinfo/centos-virt