R: Re: [Xen-users] performance problem with more than one domain U

tex---74@tiscali.it
Mon, 26 Sep 2011 14:11:42 -0000

----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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