Re: [Xen-devel] Read Performance issue when Xen Hypervisor is activated

[Michael Schinzel <schinzel@xxxxxxxxxxxxxx>]

Hello,

we have tried some more tests with the system. It seems the CPU speed ist the 
problem in this case.

I have installed the Tool unixbench. When the Hypervisor Kernel is bootet, 
Unixbench make 2.900 Benchmark Points. When we boot the same Kernel without 
Hypervisor, it generates 7.900 Benchmark Points. 

So it seems, the Hypervisor limits the CPU speed or there is somethink in 
conflict with the hypervisor. I have after this check the Intel ME Version of 
the BIOS and have seen, that it is such an old Version in this BIOS Version, 
but there is no newer BIOS Version available, maybe Supermicro stopped the 
Update Support of this Mainboard - 
https://www.supermicro.nl/products/motherboard/Xeon/C600/X9DR3-F.cfm 

So i try to Update the ME Version over an Windows Installation which is 
installed to an other disk actually.

For the benchmark, we have removed all CPU Limitations and gave the dom0 all 
available CPU ressources. So no Core Limitation. Normally we make a dom0 limit 
over grub boot configuration: 

GRUB_CMDLINE_XEN_DEFAULT="dom0_mem=16192M dom0_max_vcpus=4 dom0_vcpus_pin"

I will update you when we made an upgrade of this last thing we had not tested 
yet.


Mit freundlichen Grüßen

Michael Schinzel
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-----Ursprüngliche Nachricht-----
Von: Dario Faggioli [mailto:dario.faggioli@xxxxxxxxxx] 
Gesendet: Freitag, 30. Dezember 2016 17:35
An: Michael Schinzel <schinzel@xxxxxxxxxxxxxx>; Xen-devel 
<xen-devel@xxxxxxxxxxxxxxxxxxxx>
Cc: Roger Pau Monne <roger.paumonne@xxxxxxxxxx>; Bob Liu <bob.liu@xxxxxxxxxx>
Betreff: Re: [Xen-devel] RE: Read Performance issue when Xen Hypervisor is 
activated

[Cc-ing someone which have done disk benchmark in somewhat recent time]

On Tue, 2016-12-27 at 14:26 +0000, Michael Schinzel wrote:
> We have searched in the last days more and more for the cause of this 
> performance issue.
>  
> In cooperation with the datacenter, we change some hardware to check, 
> if the problem already proceeds. We put the RAID Controller included 
> all RAID Arrays to another Supermicro Mainboard: X10SLM-F with only 
> one CPU. The result was, we got 400 MB/s read Speed. So it seems there 
> is an issue with the Servers Mainboard / CPU and the Xen Hypervisor 
> but, we also change the Mainboard to an Supermicro X9DR3-F with the 
> actual BIOS Version 3.2a – these also do not solved the problem with 
> the performance.
>  
> What we also have done:
> -          Upgraded Hypervisor from default Debian 8 – 4.4.1 to 4.8.
> -          Tested some kernel boot configurations\
>
I think it would be useful to know more about your configuration, e.g., are 
these tests being done in Dom0? How many vCPUs and memory does Dom0 have?

> With an non hypervisor Kernel, the system also uses the read Cache of 
> the controller and after some read operations at the same file, it 
> gets 1.2 G/s back from the Cache. At Xen Hypervisor Kernel, it seems 
> the system do not use any caching operations. I also tested a bit with 
> hdparm:
>  
> root@v7:~# hdparm -Tt /dev/sdb
>  
> /dev/sdb:
> Timing cached reads:   14060 MB in  1.99 seconds = 7076.16 MB/sec 
> Timing buffered disk reads: 304 MB in  3.01 seconds = 100.85 MB/sec
>  
> This Performance is horrable. It is a RAID 10 with read/write cache 
> and SSD Caching functions.
>  
> Does somebody know how Xen proceeds with such Caching Systems?
>  
>  
> Yours sincerely
>  
> Michael Schinzel
--
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli Senior Software Engineer, 
Citrix Systems R&D Ltd., Cambridge (UK)
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