[CentOS] how to optimize CentOS XEN dom0?

Tue Feb 22 23:40:02 UTC 2011
Cameron Kerr <cameron at humbledown.org>

On 23/02/11 12:29, Rudi Ahlers wrote:
> Hi,
> 
> I have a problematic CentOS XEN server and hope someone could point me
> in the right direction to optimize it a bit.
> 
> The server runs on a Core2Quad 9300, with 8GB RAM (max motherboard can
> take, 1U chassis) on an Intel motherboard with a 1TB SATA HDD.
> 
> dom0 is set to 512MB limit with a few small XEM VM's running:
> 
> 
> root at zaxen01:[~]$ xm list
> Name                                      ID Mem(MiB) VCPUs State   Time(s)
> Domain-0                                   0      512     4 r-----     96.5

dom0 is responsible for IO, so you would normally expect it have it
spend more time in the CPU. You could try pinning it to its own CPU...

> actionco.vm                                3     1519     1 -b----     14.8
> byracers.vm                                4      511     1 -b----     85.7
> ns1                                        5      511     1 -b----     22.3
> picturestravel                            6      255     1 -b----     13.3
> rafttheworld                               7      255     1 -b----     11.3
> zafepres.vm                                8      511     1 -b----     19.0
> 
> 
> 
> 
> the server itself seems to eat up a lot of resources:
> 
> 
> root at zaxen01:[~]$ free -m
>              total       used       free     shared    buffers     cached
> Mem:           512        472         39          0         13        215
> -/+ buffers/cache:        244        268
> Swap:         4095          0       4095[/CODE]

This looks normal. Remember, Linux uses a "memory full" model, so
although it appears that there is 39MB of real memory available, there
is actually 268, with most of that being used to cache filesystem data.

If you want to see how loaded a system is, with respect to memory
pressure, try using 'vmstat' and look for how often it is swapping pages
into and out of swap.

Also, have a look at the Xen users guide. It has some
performance-enhancing tips that you should be aware of. In particular,
realise that dom0 is a little special, particularly with regard to IO.

> Is there anything I can optimize on such a server?

Not entirely sure what you need to optimise at this point. So far I see
a reasonably normal-looking system (although, to be frank, I don't have
a lot of experience with Xen at present).

Hope it helps,
Cameron