XP installation speed: KVM vs Xen

XP installation speed: KVM vs Xen

[Andrew Olney]

I've been migrating from Xen to KVM for a wide variety of reasons.

I've noticed, however, that XP installs much much faster with Xen (3.03
xen-image-xen0-2.6.17-6-generic-xen0 ubuntu) than with KVM (14).

I haven't clocked it, but for KVM it takes longer than realtime (by the
XP install clock) and with Xen it takes less than realtime.

I assume that this is all file I/O related, which raises the question:
what file system setup optimizes KVM I/O, e.g. qcow vs. raw?


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Re: XP installation speed: KVM vs Xen

[Andreas Hasenack]

On Tuesday 27 February 2007 17:46:45 Andrew Olney wrote:
> I've been migrating from Xen to KVM for a wide variety of reasons.
>
> I've noticed, however, that XP installs much much faster with Xen (3.03
> xen-image-xen0-2.6.17-6-generic-xen0 ubuntu) than with KVM (14).
>
> I haven't clocked it, but for KVM it takes longer than realtime (by the
> XP install clock) and with Xen it takes less than realtime.
>
> I assume that this is all file I/O related, which raises the question:
> what file system setup optimizes KVM I/O, e.g. qcow vs. raw?

I experienced very slow graphic performance with kvm, could that be related 
too?

For example, graphic grub boot splash is very slow, as is any form of frame 
buffer boot in linux.

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Re: XP installation speed: KVM vs Xen

[Anthony Liguori]

Andreas Hasenack wrote:
> On Tuesday 27 February 2007 17:46:45 Andrew Olney wrote:
>   
>> I've been migrating from Xen to KVM for a wide variety of reasons.
>>
>> I've noticed, however, that XP installs much much faster with Xen (3.03
>> xen-image-xen0-2.6.17-6-generic-xen0 ubuntu) than with KVM (14).
>>
>> I haven't clocked it, but for KVM it takes longer than realtime (by the
>> XP install clock) and with Xen it takes less than realtime.
>>
>> I assume that this is all file I/O related, which raises the question:
>> what file system setup optimizes KVM I/O, e.g. qcow vs. raw?
>>     
>
> I experienced very slow graphic performance with kvm, could that be related 
> too?
>
> For example, graphic grub boot splash is very slow, as is any form of frame 
> buffer boot in linux.
>   

Graphic grub boot is different from the rest of graphics and should not 
be any worse than Xen.

Regards,

Anthony Liguori

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Re: XP installation speed: KVM vs Xen

[Anthony Liguori]

Andrew Olney wrote:
> I've been migrating from Xen to KVM for a wide variety of reasons.
>
> I've noticed, however, that XP installs much much faster with Xen (3.03
> xen-image-xen0-2.6.17-6-generic-xen0 ubuntu) than with KVM (14).
>
> I haven't clocked it, but for KVM it takes longer than realtime (by the
> XP install clock) and with Xen it takes less than realtime.
>
> I assume that this is all file I/O related, which raises the question:
> what file system setup optimizes KVM I/O, e.g. qcow vs. raw?
>   

Xen should outperform KVM wrt disk performance.  Xen is based on QEMU 
0.8.2 and has a ton of patches including one that aggressive reports IO 
completions to the host asynchronously.

KVM uses a version of QEMU that is significantly closer to mainline QEMU 
(almost no changes that aren't KVM related).  Eventually, all of the KVM 
changes should make it into mainline QEMU whereas that probably will 
never happen with Xen.

QEMU only got asynchronous IO support in 0.9.0.  Unfortunately, the 
implementation actually results in a regression in performance.  Some 
hacks can fix it though.

Of course, the SCSI emulation in 0.9.0 improves performance by quite a 
lot (to the point where it's better than Xen).  However, some work is 
needed to make SCSI disks bootable and to expose SCSI command line options.

Regards,

Anthony Liguori

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>   


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Re: XP installation speed: KVM vs Xen

[Avi Kivity]

Andrew Olney wrote:
> I've been migrating from Xen to KVM for a wide variety of reasons.
>
> I've noticed, however, that XP installs much much faster with Xen (3.03
> xen-image-xen0-2.6.17-6-generic-xen0 ubuntu) than with KVM (14).
>
> I haven't clocked it, but for KVM it takes longer than realtime (by the
> XP install clock) and with Xen it takes less than realtime.
>
> I assume that this is all file I/O related, which raises the question:
> what file system setup optimizes KVM I/O, e.g. qcow vs. raw?
>   

The best file format is not a file, but a raw partition or lvm volume.  
Second best is a raw partition that has been prewritten using dd.

Pinning kvm to a cpu may help; try prefixing the command with 'taskset 1'.

Please report you experiences, especially about the last hack, as it 
indicate a serious problem.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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Re: XP installation speed: KVM vs Xen

[Avi Kivity]

Andrew Olney wrote:
> I've been migrating from Xen to KVM for a wide variety of reasons.
>
> I've noticed, however, that XP installs much much faster with Xen (3.03
> xen-image-xen0-2.6.17-6-generic-xen0 ubuntu) than with KVM (14).
>   


btw, as both Xen and kvm use qemu, Xen full virtualization images should 
work without change in kvm.



-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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Re: XP installation speed: KVM vs Xen

[Andrew Olney]

I'd almost swear that KVM is faster with an XP raw image that was
installed by Xen, than it is with a raw image installed by KVM.

On Wed, 2007-02-28 at 09:10 +0200, Avi Kivity wrote:
> Andrew Olney wrote:
> > I've been migrating from Xen to KVM for a wide variety of reasons.
> >
> > I've noticed, however, that XP installs much much faster with Xen (3.03
> > xen-image-xen0-2.6.17-6-generic-xen0 ubuntu) than with KVM (14).
> >   
> 
> 
> btw, as both Xen and kvm use qemu, Xen full virtualization images should 
> work without change in kvm.
> 
> 
> 


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Re: XP installation speed: KVM vs Xen

[Avi Kivity]

Andrew Olney wrote:
> I'd almost swear that KVM is faster with an XP raw image that was
> installed by Xen, than it is with a raw image installed by KVM.
>
>   

That may well be.  Perhaps the images have different HALs.

Compare the values under My Computer | Properties | Hardware | Device 
Manager | Computer.  Maybe one uses the "Standard PC" HAL (faster) and 
the other the ACPI HAL (slower).  You can also change HALs (required 
reboot).


> On Wed, 2007-02-28 at 09:10 +0200, Avi Kivity wrote:
>   
>> Andrew Olney wrote:
>>     
>>> I've been migrating from Xen to KVM for a wide variety of reasons.
>>>
>>> I've noticed, however, that XP installs much much faster with Xen (3.03
>>> xen-image-xen0-2.6.17-6-generic-xen0 ubuntu) than with KVM (14).
>>>   
>>>       
>> btw, as both Xen and kvm use qemu, Xen full virtualization images should 
>> work without change in kvm.
>>
>>
>>
>>     
>
>   


-- 
error compiling committee.c: too many arguments to function


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Re: XP installation speed: KVM vs Xen

[Andrew Olney]

The Xen installed image is "Standard PC". I erased the KVM installed
image unfortunately, so  I can't check that easily.

The KVM installed image did require the -no-acpi flag, and the Xen image
does not, so that is consistent with your explanation: the Xen install
is a faster, non-acpi HAL.

The speed difference is quite noticeable on a core 2 1.66


On Wed, 2007-02-28 at 18:40 +0200, Avi Kivity wrote:
> Andrew Olney wrote:
> > I'd almost swear that KVM is faster with an XP raw image that was
> > installed by Xen, than it is with a raw image installed by KVM.
> >
> >   
> 
> That may well be.  Perhaps the images have different HALs.
> 
> Compare the values under My Computer | Properties | Hardware | Device 
> Manager | Computer.  Maybe one uses the "Standard PC" HAL (faster)
> and 
> the other the ACPI HAL (slower).  You can also change HALs (required 
> reboot).
> 
> 
> > On Wed, 2007-02-28 at 09:10 +0200, Avi Kivity wrote:
> >   
> >> Andrew Olney wrote:
> >>     
> >>> I've been migrating from Xen to KVM for a wide variety of reasons.
> >>>
> >>> I've noticed, however, that XP installs much much faster with Xen
> (3.03
> >>> xen-image-xen0-2.6.17-6-generic-xen0 ubuntu) than with KVM (14).
> >>>   
> >>>       
> >> btw, as both Xen and kvm use qemu, Xen full virtualization images
> should 
> >> work without change in kvm.
> >>
> >>
> >>
> >>     
> >
> >   
> 
> 
> -- 
> error compiling committee.c: too many arguments to function
> 
> 


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