Xen users - Sep 2011 - R: Re: performance problem with more than one domain U

----Messaggio originale----
Da: todd.deshane@xen.org
Data: 25/09/2011 
4.37
> So the VMs have very different configurations then?
> Have you 
tried giving the 2 VMs equal resources?
> Why wouldn''t you expect a 
virtual machine with less vCPUs and less memory to perform slower?

OK, 
maybe I did not explain very well the situation in my previous post.


Let''s say I have 2 VM, called VM "A" and VM "B"

VM "A" has 8 vcpus and 
12 GB RAM

VM "B" has  1 vcpu and 2 GB RAM

Now, I start the VM A and 
from the VM A I do the command time rm -r  /mydir and I have this time:


0.15 user 
0.60 system 
3:46.79 elapsed

Then I start the VM "B". I 
just start it, but I am always logged to VM "A".

At this point I 
launch another time the command "time rm -r  /mydir" ALWAYS FROM VM 
"A", not B!
And, on the same VM, this time I have:
0.00 user 
0.56 
system 
15:33.38 elapsed

The only difference is that now domain "B" is 
running.
>The rm command might not get the best benchmark to to 
understand what
>is going on. Have you considered testing a 
microbenchmark like iozone?

I also did the command:

hdparm -tT 
/dev/mapper/myserver-root

Strange thing, this always perform similar


when the rm command took 8:42 minutes:
 Timing cached reads:   5700 MB 
in  1.99 seconds = 2857.98 MB/sec
 Timing buffered disk reads:  120 MB 
in  3.02 seconds =  39.75 MB/sec

when the rm command took 1:27 
minutes:
 Timing cached reads:   5466 MB in  1.99 seconds = 2740.00 
MB/sec
 Timing buffered disk reads:  146 MB in  3.01 seconds =  48.48 
MB/sec

>What is your disk backend and is it the same for each? It is 
a shared
>directory or are you creating/copying the same directory to 
each
>machine for the test?
As explained above it is the same VM.

I 
should add that at hardware level (i.e. dom0) I have an Adaptec Raid 
Card with four 2 GB SATA hard disks in a RAID 10 configuration, if 
that''s matter

Thank You for everything

Mario



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On Mon, Sep 26, 2011 at 10:10 AM, tex---74@tiscali.it
<tex---74@tiscali.it> wrote:
> OK,
> maybe I did not explain very well the situation in my previous post.
>
>
> Let''s say I have 2 VM, called VM "A" and VM
"B"
>
> VM "A" has 8 vcpus and
> 12 GB RAM
>
> VM "B" has  1 vcpu and 2 GB RAM
>
> Now, I start the VM A and
> from the VM A I do the command time rm -r  /mydir and I have this time:
>
>
> 0.15 user
> 0.60 system
> 3:46.79 elapsed
>
> Then I start the VM "B". I
> just start it, but I am always logged to VM "A".
>
> At this point I
> launch another time the command "time rm -r  /mydir" ALWAYS FROM
VM
> "A", not B!
> And, on the same VM, this time I have:
> 0.00 user
> 0.56
> system
> 15:33.38 elapsed
>
> The only difference is that now domain "B" is
> running.
Ah, OK I understand now. Try using xentop and drilling down into disk
I/O to see if VM B is using up some of the I/O bandwidth/resources for
some reason.

There''s no reason the system shouldn''t be able to handle
another small VM...

-- 
Todd Deshane
http://www.linkedin.com/in/deshantm
http://www.xen.org/products/cloudxen.html
http://runningxen.com/

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