[CentOS-virt] poor performance with dom0 on centos7

Pasi Kärkkäinen pasik at iki.fi
Thu Sep 17 07:29:20 UTC 2015


On Wed, Sep 16, 2015 at 09:46:52PM +0200, Christoph wrote:
> Hi
>

Hi,
 
> 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] process...
> 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 load
> 

Are you using nfs over UDP or TCP ? 

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

I don't think.

> Any hints for me?
> 

If you used NFS over UDP, try running it over TCP.

What does 'top' and/or 'iostat -x 1' say during the 'benchmark'  ?


-- Pasi

> 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)
> 
> -- 
> ------
> Greetz
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