[CentOS-virt] poor performance with dom0 on centos7

Wed Sep 16 19:55:31 UTC 2015
Christoph <mangel at gmx.de>


Im now pretty sure the problem is the DomU with NFS Server.

If I write on a NFS share from other Host (bare metal or other vm) then 
I see on my NFS server nearly the whole time 100% io at [jbd2/dm-5-8] 
If I write on a SMB share (same partition as nfs share) from other Host 
then it is a little bit better but still ever and ever again 100% io 

If I write a 1GB file on the same partition (with nfs/samba share) with 
dd, I dont see the high io load...

Is there a known problem with nfs/smb shares and/or dm in xen domU's on 
centos 7 as dom0? With centos 6 as dom0 I didnt had the problem...
(the partition with the shares is a raid5 software partition, soft raid 
is build in dom0 and as a xvd device passed through to the domU with the 

could selinux be the problem? I have it in permissive mode on all hosts 
here (dom0 and domU) not disabled...

Any hints for me?

Am 2015-09-01 06:47, schrieb Christoph:
> Hi All
> it is possible to tune dom0/domU for better IO/network performance?
> Since I have changed to Cenots7 dom0, I have a really poor IO
> performance inside a PV VM.
> I have already done what is described on
> http://wiki.xenproject.org/wiki/Tuning_Xen_for_Performance
> It is better now but still significantly worse than with centos6 dom0
> my settings:
> xen parameter: dom0_mem=1024M cpufreq=xen dom0_max_vcpus=2 
> dom0_vcpus_pin
> xl sched-credit
> Cpupool Pool-0: tslice=30ms ratelimit=1000us
> Name                                ID Weight  Cap
> Domain-0                             0   1024    0
> samael                               1    256    0
> satan                                2    512    0
> amon                                 3    256    0
> leviathan                            4    512    0
> echo 1048576 > /proc/sys/net/ipv4/tcp_limit_output_bytes on dom0
> the both domU's satan and leviathan are very IO performance oriented
> (NFS server and downloading vm)
> Is there something more what I can do or try?
> could it be a selinux issue? I have it in permissive mode there, not
> disabled. But permissive means only to collect the info not enforcing
> the rules...
> (I use the xen45 pkgs)