Re: Couple of quetsions HD perf, mac address...

Re: Couple of quetsions HD perf, mac address...

[Gregory Haskins]

On Tue, 2007-07-03 at 11:43 +0200, Benjamin Budts wrote:
> 3* When I specify a mac address for my debian virtual machine eth0 
> changes to eth3 ... very very weird... it's not that bad, i just changed 
> my interfaces config file from eth0 to eth3, but it's a bit weird

Many linux distros support persistent naming these days.  Therefore,
there is some record that in the past eth0 had mac X.  Now it that sees
an interface with mac Y, it assumes its a new interface and renames it
something unique.

I am assuming this is the behavior you are seeing.



> 
> My windows xp seems to boot without a problem when specifying another 
> mac addr
> 

Out of curiosity, does Windows rename it to "Local Connection 2" (etc)
when you change the mac addr?

> Did you guys have that problem  yet ? How can I fix it please ?

If its the problem I am describing, do a google search for where debian
maintains its persistence data and blow it away (or adjust the record
for eth0 to have your new mac)




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Re: Couple of quetsions HD perf, mac address...

[Benjamin Budts]

Gregory Haskins wrote:
> On Tue, 2007-07-03 at 11:43 +0200, Benjamin Budts wrote:
>   
>> 3* When I specify a mac address for my debian virtual machine eth0 
>> changes to eth3 ... very very weird... it's not that bad, i just changed 
>> my interfaces config file from eth0 to eth3, but it's a bit weird
>>     
>
> Many linux distros support persistent naming these days.  Therefore,
> there is some record that in the past eth0 had mac X.  Now it that sees
> an interface with mac Y, it assumes its a new interface and renames it
> something unique.
>
> I am assuming this is the behavior you are seeing.
>
>   
Aah that would explain why i'm having eth3... I started it up 2 or 3 
times with another mac as well, so he cached it probably like you said...

thx for that !


>
>   
>> My windows xp seems to boot without a problem when specifying another 
>> mac addr
>>
>>     
>
> Out of curiosity, does Windows rename it to "Local Connection 2" (etc)
> when you change the mac addr?
>
>   
No it's not changed from Local connection --> Local connection 2 ...
>> Did you guys have that problem  yet ? How can I fix it please ?
>>     
>
> If its the problem I am describing, do a google search for where debian
> maintains its persistence data and blow it away (or adjust the record
> for eth0 to have your new mac)
>
>
>
>
>   

Any clues about the HD performance, do you notice the same behaviour ?

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Re: Couple of quetsions HD perf, mac address...

[Laurent Vivier]

[-- Attachment #1.1: Type: text/plain, Size: 1714 bytes --]

Benjamin Budts wrote:
> Gregory Haskins wrote:
>> On Tue, 2007-07-03 at 11:43 +0200, Benjamin Budts wrote:
>>   
>>> 3* When I specify a mac address for my debian virtual machine eth0 
>>> changes to eth3 ... very very weird... it's not that bad, i just changed 
>>> my interfaces config file from eth0 to eth3, but it's a bit weird
>>>     
>> Many linux distros support persistent naming these days.  Therefore,
>> there is some record that in the past eth0 had mac X.  Now it that sees
>> an interface with mac Y, it assumes its a new interface and renames it
>> something unique.
>>
>> I am assuming this is the behavior you are seeing.
>>
>>   
> Aah that would explain why i'm having eth3... I started it up 2 or 3 
> times with another mac as well, so he cached it probably like you said...
> 
> thx for that !

udev manages this.
each time you start udev, it executes
/etc/udev/rules.d/z45_persistent-net-generator.rules that generates eth(X)
definitions according MAC address. A new MAC address creates a new eth(X+1)
interface.

I don't know if it is clean, but to avoid this behaviour, I remove
/etc/udev/rules.d/z45_persistent-net-generator.rules (which is a link).

If you only want to clean this, you can remove only the file
/etc/udev/rules.d/z25_persistent-net.rules which will be re-generated by
z45_persistent-net-generator.rules at next reboot (or udev restart):
rm /etc/udev/rules.d/z25_persistent-net.rules
invoke-rc.d udev stop
invoke-rc.d udev start

Regards,
Laurent
-- 
------------- Laurent.Vivier-6ktuUTfB/bM@public.gmane.org  --------------
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  indistinguishable from magic." - Arthur C. Clarke


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Re: Couple of quetsions HD perf, mac address...

[Gregory Haskins]

On Tue, 2007-07-03 at 13:21 +0200, Benjamin Budts wrote:

> Any clues about the HD performance, do you notice the same behaviour ?

I haven't run any benchmarks myself, but it is to be expected that IO
will be slower in a VM. :(  There are efforts underway to improve this,
however.  For instance, a paravirtualized scsi driver for the guest is
being developed which allows the guest to more efficiently send and
receive disk IO between the VM and host.  This should allow it to get
much closer to native performance.

-Greg




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Couple of quetsions HD perf, mac address...

[Benjamin Budts]

Hi there,

Sorry to bother the developpers list, I have couple of questions...

I've been testing kvm for couple of months with the following hardware :
S5000pal intel board
1x Duo Core Xeon 2.4
2048Gb DDR2 667 Ram
Western digital SATA 150 10K rpm disk.

I run kvm21 at the moment...(I need to upgrade asap of course ;) )

And have the following questions :

1* When i run hdparm -t /dev/sda1 I have 80-85Mbit/s read speed on my 
guest os (debian etch)

If I run it ''in'' a virtual machine (using also debian Etch with 
2.6.21.5 kernel) I get : 28-35Mbits...

I even tried to put the image on a seperate disk to be able to have 
more, but I can't get more then 35Mbits out of it...

How can I up the disk performance without having to replace everything 
by SCSI hardware ?

2* When will smp be supported in the VM ? Would love to test the 
performance by starting up the virtual machine with the -smp 2 
command...Kernel hangs at the moment
(I read you guys put it on the commit list, and you're working on it...)

3* When I specify a mac address for my debian virtual machine eth0 
changes to eth3 ... very very weird... it's not that bad, i just changed 
my interfaces config file from eth0 to eth3, but it's a bit weird

My windows xp seems to boot without a problem when specifying another 
mac addr

Did you guys have that problem  yet ? How can I fix it please ?


Keep up the good work, lovely product !

thx
Ben

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Re: Couple of quetsions HD perf, mac address...

[Dor Laor]

>1* When i run hdparm -t /dev/sda1 I have 80-85Mbit/s read speed on my
>guest os (debian etch)
>
>If I run it ''in'' a virtual machine (using also debian Etch with
>2.6.21.5 kernel) I get : 28-35Mbits...
>
>I even tried to put the image on a seperate disk to be able to have
>more, but I can't get more then 35Mbits out of it...
>
>How can I up the disk performance without having to replace everything
>by SCSI hardware ?

As Greg mentioned, PV-scsi drivers are good when implemented.
There is also unmerged PV driver for ide disks developed by RedHat.
By the end of the year we'll probably handle it better.

>
>2* When will smp be supported in the VM ? Would love to test the
>performance by starting up the virtual machine with the -smp 2
>command...Kernel hangs at the moment
>(I read you guys put it on the commit list, and you're working on
it...)

It's work in progress, the current state is that smp Linux can boot but
it's 
not stable yet. I guess it's a matter of several months to stabilze.

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Re: Couple of quetsions HD perf, mac address...

[Laurent Vivier]

[-- Attachment #1.1: Type: text/plain, Size: 1286 bytes --]

Benjamin Budts wrote:
[snip]
> 1* When i run hdparm -t /dev/sda1 I have 80-85Mbit/s read speed on my 
> guest os (debian etch)
> 
> If I run it ''in'' a virtual machine (using also debian Etch with 
> 2.6.21.5 kernel) I get : 28-35Mbits...
> 
> I even tried to put the image on a seperate disk to be able to have 
> more, but I can't get more then 35Mbits out of it...
> 
> How can I up the disk performance without having to replace everything 
> by SCSI hardware ?
> 

You can improve performance by using virtual SCSI disks. I post some
benchchmarks with dbench on this list at the end of may (24/05).

QEmu (and thus KVM) doesn't support natively SCSI disk for the PC virtual
machine. I post a patch the 1st of march on QEmu mailing list to add a "-sda"
parameter to use SCSI disk (but my approach was not approved by maintainers).
The problem with the virtual SCSI is you cannot boot on it because there is no
BIOS to manage it. But you can use it as storage and boot linux using the
parameter "-kernel" to load directly the kernel from the host disk.

Regards,
Laurent
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  indistinguishable from magic." - Arthur C. Clarke


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Re: Couple of quetsions HD perf, mac address...

[Laurent Vivier]

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Benjamin Budts wrote:
> 
> Hi Laurent,
> 
> Intresting stuff, could you send me your patch and the benchmarks please ?
> I think I might try it out.


patch:

http://permalink.gmane.org/gmane.comp.emulators.qemu/15969

benchmarks:

http://permalink.gmane.org/gmane.comp.emulators.kvm.devel/3373

> thx a lot
> 
> Laurent Vivier wrote:
>> Benjamin Budts wrote:
>> [snip]
>>  
>>> 1* When i run hdparm -t /dev/sda1 I have 80-85Mbit/s read speed on my
>>> guest os (debian etch)
>>>
>>> If I run it ''in'' a virtual machine (using also debian Etch with
>>> 2.6.21.5 kernel) I get : 28-35Mbits...
>>>
>>> I even tried to put the image on a seperate disk to be able to have
>>> more, but I can't get more then 35Mbits out of it...
>>>
>>> How can I up the disk performance without having to replace
>>> everything by SCSI hardware ?
>>>
>>>     
>>
>> You can improve performance by using virtual SCSI disks. I post some
>> benchchmarks with dbench on this list at the end of may (24/05).
>>
>> QEmu (and thus KVM) doesn't support natively SCSI disk for the PC virtual
>> machine. I post a patch the 1st of march on QEmu mailing list to add a
>> "-sda"
>> parameter to use SCSI disk (but my approach was not approved by
>> maintainers).
>> The problem with the virtual SCSI is you cannot boot on it because
>> there is no
>> BIOS to manage it. But you can use it as storage and boot linux using the
>> parameter "-kernel" to load directly the kernel from the host disk.
>>
>> Regards,
>> Laurent
>>   
> 
> 


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