Re: [Xen-devel] Disk iops performance scalability

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Mar 18, 2013 at 11:23:00PM +0000, John Morrison wrote:
> Hi,
> 
> Seeing a drop-off in iops when more vcpu's are added:-
> 
> 3.8.2 kernel/xen-4.2.1/single domU/LVM backend/8GB RAM domU/2GB RAM dom0
> 
> dom0_max_vcpus=2 dom0_vcpus_pin
> 
> domU  8 cores  fio result 145k iops
> domU 10 cores fio result 99k iops
> domU 12 cores fio result 89k iops 
> domU 14 cores fio result 81k iops
> 
> ioping . -c 3
> 4096 bytes from . (ext4 /dev/xvda1): request=1 time=0.1 ms
> 4096 bytes from . (ext4 /dev/xvda1): request=2 time=0.7 ms
> 4096 bytes from . (ext4 /dev/xvda1): request=3 time=0.8 ms
> 
> --- . (ext4 /dev/xvda1) ioping statistics ---
> 3 requests completed in 2002.0 ms, 1836 iops, 7.2 mb/s
> min/avg/max/mdev = 0.1/0.5/0.8/0.3 ms
> 
> The initial ioping response is good, then a lot of latency with later ones. 
> Any ideas ?

Is your guest compiled with PARAVIRT_SPINLOCK and are you using a PV or PVHVM 
guest?

> 
> Thanks
> 
> John
> 
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> 

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