[Xen-devel] Disk iops performance scalability

[John Morrison <john@xxxxxxxxxxxxx>]

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 ?

Thanks

John

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